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Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. Only use this test to diagnose the following:

NOTE: HO2S may be displayed on scan tool as 02S.

To prevent replacement of good components, be aware the following non-EEC areas may be cause of driveability problems:

NOTE: Test procedure begins with step 20). No test procedures have been omitted.

  1. 20) Continuous Memory DTCs P0133 Or P0153: Perform KOER Self-Test

    Perform KOER ON-DEMAND SELF-TEST . If DTC P1127, P1128 or P1129 is present, go to appropriate system test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If DTC P1127, P1128 or P1129 are not present, go to next step.

  2. 21) DTC P0133 & P0153: HO2S Response Test

    DTC P0133 or P0153 are set during self-test when frequency and amplitude fall below a calibrated limit in HO2S as follows:

    Possible causes are:

    • HO2S Sensor Contaminanted
    • Exhaust Leaks
    • Open Or Shorted Circuit
    • Improper Fueling
    • Faulty MAF Sensor
    • Deteriorating HO2S Sensor
    • Leak In Air Induction System

    Turn ignition switch to ON position. Using scan tool, access GENERIC OBD-II FUNCTIONS and press enter. Press CONTINUE. Select DIAGNOSTIC MONITORING TEST RESULTS from menu and press enter. Scroll to TEST ID: 01 and press enter. Press START. If measured value is less than minimum threshold, go to step  23). If measured value is greater than minimum threshold, fault cannot be identified at this time. Perform PCM RESET PROCEDURE  under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Perform DRIVE CYCLE PROCEDURES  under ADDITIONAL SYSTEM FUNCTIONS. Ensure HEGO MONITOR PROCEDURE is performed. Repeat step  20). If DTCs P1127, P1128 or P1129 are not present, testing is complete.

    Fig 1: Locating HO2S (4-Cylinder)
    G95I35970Courtesy of FORD MOTOR CO.
    Fig 2: Locating HO2S (V6 With Dual Exhaust)
    G95A35972Courtesy of FORD MOTOR CO.
    Fig 3: Locating HO2S (V6 With Single Exhaust)
    G95B35973Courtesy of FORD MOTOR CO.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 21) to step 23). No test procedures have been omitted.

  3. 23) Check For Unmetered Air Leaks

    Fuel calculations can be affected by ummetered air (vacuum) leaks. Check the following as potential source of air leak:
    • Hoses Connected To MAF Sensor Or Throttle Body Leaking
    • Intake Manifold Gasket Leaking
    • PCV System Disconnected
    • Vacuum Lines Disconnected
    • Poorly Seated Oil Dip Stick &/Or Dipstick Tube Or Cap
    • Exhaust Leaks At Flanges Or Gaskets

    If none of these conditions are present, go to next step. If any of these conditions are present, repair source of air leak as necessary. Perform PCM RESET PROCEDURE  under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Perform DRIVE CYCLE PROCEDURES  under ADDITIONAL SYSTEM FUNCTIONS. Ensure HEGO MONITOR PROCEDURE is performed.

    NOTE: HO2S may be displayed as O2S on scan tool.

  4. 24) Check HO2S Circuits

    Turn ignition switch to OFF position. Disconnect suspect HO2S harness connector. Check for water contamination. Clean and repair as necessary. Connect a jumper wire between suspect HO2S harness connector HO2S SIG and VPWR terminals. See Fig 4. Turn ignition switch to ON position. Using scan tool, select appropriate HO2S PID from PID/DATA MONITOR & RECORD menu.

    If HO2S PID voltage is 1.5 volts or less, remove jumper wire and go to next step. If HO2S PID voltage is more than 1.5 volts, replace faulty HO2S and change engine oil and filter. Perform PCM RESET PROCEDURE  under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Perform DRIVE CYCLE PROCEDURES  under ADDITIONAL SYSTEM FUNCTIONS. Ensure HEGO MONITOR PROCEDURE is performed.

    Fig 4: Identifying HO2S Connector Terminals (Typical)
    G95E35968Courtesy of FORD MOTOR CO.

  5. 25) DTCs P0141 & P0161: Check HO2S Heater, SIG Or SIGRTN Circuits For Open

    DTC P0141 or P0161 are set during self-test when current draw exceeds a calibrated limit or an open or short is detected in HO2S heater as follows:

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Check HO2S circuit for exposed wiring, water contamination, corrosion and proper assembly. Repair as necessary. Using a DVOM, measure resistance of suspect HO2S SIG circuit between PCM harness connector terminal and HO2S harness connector terminal. See HO2S PCM TERMINAL IDENTIFICATION  table. See Fig 4.

    Using a DVOM, measure resistance of suspect SIG RTN circuit between PCM harness connector terminal and HO2S harness connector terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Fig 4. If both resistance measurements are less than 5 ohms, go to next step. If either resistance measurement is 5 ohms or more, repair open in HO2S SIG or SIG RTN circuit. Perform DRIVE CYCLE PROCEDURES  under ADDITIONAL SYSTEM FUNCTIONS. Ensure HEGO MONITOR PROCEDURE is performed.

    PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION

    Application PCM Terminal No.
    All Models
    HO2S-11 SIG 60
    HO2S-11 HTR 93
    HO2S-12 SIG 35
    HO2S-12 HTR 95
    HO2S-21 SIG 87
    HO2S-21 HTR 94
    HO2S-22 SIG 61
    HO2S-22 HTR 96
    PWR GND 51, 77 & 103
    SIG RTN 91
    VPWR 71 & 97
    VREF 90

  6. 26) Check HO2S SIG Circuit For Short To VPWR

    Disconnect scan tool from Data Link Connector (DLC). Using a DVOM, measure resistance between PCM harness connector HO2S and VPWR terminals. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure. If resistance measurement is more than 10 k/ohms, go to next step. If resistance measurement is 10 k/ohms or less, go to step  28).

  7. 27) Check For Source Of Potential HO2S Contamination

    Check the following areas for cause of contamination:
    • Use Of Unapproved Silicone Sealers
    • Fuel Contaminated By Silicone Fuel Additives
    • Excessive Oil Burning
    • Antifreeze Leaking Internally In Engine
    • Lead Contaminated Fuel
    • Short Trip Driving In Cold Weather
    • Use Of Unapproved Cleaning Products

    If contamination exists, repair source of contamination and replace faulty HO2S, oil and filter. Perform PCM RESET PROCEDURE  under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. Perform DRIVE CYCLE PROCEDURES  under ADDITIONAL SYSTEM FUNCTIONS. Ensure HEGO MONITOR PROCEDURE is performed. If contamination does not exist and you were directed here to diagnose DTC P0141 or P0161, go to step  30), for all others replace PCM.

  8. 28) Verify Wiring Is In Proper Terminal Location

    Ensure ignition switch is turned to OFF position. Disconnect suspect HO2S harness connector. Ensure PCM is disconnected. Inspect connectors for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance of HO2S SIG circuit between PCM harness connector terminal and HO2S harness connector terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Fig 4. Using a DVOM, measure resistance of SIG RTN circuit between PCM harness connector terminal and HO2S harness connector terminal. If both resistance measurements are less than 5 ohms, replace HO2S. If either resistance measurement is 5 ohms or more, repair wiring as necessary.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 28) to step 30). No test procedures have been omitted.

  9. 30) DTC P0135 Or P0155: HO2S Heater Circuit Shorted To GND Or VPWR, Or Excessive Or Low Current Draw

    These DTCs indicate a short to VPWR, or an open VPWR or GND circuit in HO2S heater circuit causing current draw to exceed calibrated limit. HO2S DTC identification is as follows:
    • DTC P0135 Is For HO2S-11
    • DTC P0141 Is For HO2S-12
    • DTC P0155 Is For HO2S-21
    • DTC P0161 Is For HO2S-22

    Refer to illustrations for HO2S identification. See Fig 1-Fig 3 . Possible causes are:

    • Short To VPWR Or HO2S Circuit
    • Water In Connectors
    • Open In GND Or VPWR Circuit
    • Low Battery Voltage
    • Corroded Or Poorly Connected Terminals
    • Damaged HO2S Heater
    • Damaged Powertrain Control Module (PCM)
    • Faulty HO2S Heater

    Inspect HO2S circuit for exposed wiring, water contamination, corrosion and proper assembly. Repair as necessary. If HO2S connectors are okay, go to next step.

  10. 31) Perform KOEO On-Demand Self-Test

    Start engine and operate at 2000 RPM for one minute. Turn ignition switch to OFF position. Perform KOEO ON-DEMAND SELF-TEST . If DTC P0135, P0141, P0155 or P0161 is present, go to next step. If specified DTCs are not present, go to step  33).
    11. NOTE: If pairs of DTCs P0135 and P0155, or P0141 and P0161 are retrieved, both HO2S HTR circuits will require testing. DTCs retrieved individually, are to be tested individually.

  11. 32) Check VPWR Voltage To HO2S HTR Circuit Harness Connector
    Turn ignition switch to OFF position. Disconnect suspect HO2S harness connector. Inspect wiring harness for damage and repair as necessary. Turn ignition switch to ON position. Using a DVOM, measure voltage between suspect HO2S harness connector SIG RTN and VPWR terminals. See Fig 4. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, check VPWR circuit fuse. Replace as necessary. If VPWR circuit fuse is okay, repair open in VPWR circuit. See WIRING DIAGRAMS article.

  12. 33) Check HO2S HTR Circuit For Short To GND Or VPWR

    Turn ignition switch to OFF position. Disconnect scan tool from DLC. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance between PCM harness connector suspect HO2S HTR circuit terminal and PWR GND terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION . See Fig 4. Using a DVOM, measure resistance between suspect HO2S harness connector HO2S HTR terminal and SIG RTN and VPWR terminals. If all resistance measurements are more than 10 k/ohms, go to next step. If any resistance measurement is 10 k/ohms or less, repair short in affected circuit.

  13. 34) Check HO2S HTR Circuit For Open

    Leave ignition switch turned to OFF position and HO2S disconnected. Using a DVOM, measure resistance of suspect HO2S HTR circuit between PCM harness connector terminal and suspect HO2S harness connector terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Fig 4. If resistance is 5 ohms or more, repair open circuit or excessive resistance in HTR circuit. If resistance is less than 5 ohms, go to next step.

  14. 35) Check HO2S HTR Resistance

    Turn ignition switch to OFF position. With suspect sensor disconnected, measure resistance between suspect HO2S connector HO2S HTR and VPWR terminals. If resistance is 3-30 ohms, go to next step. If resistance is not 3-30 ohms, replace HO2S.

  15. 36) Check HO2S Case For Short To VPWR, HTR Or SIG RTN

    Using a DVOM, measure resistance between HO2S component case and HO2S connector HO2S HTR, SIG RTN and VPWR terminals. If all resistance measurements are more than 10 k/ohms, replace PCM. If any resistance measurement is 10 k/ohms or less, replace HO2S.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 36) to step 40). No test procedures have been omitted.

  16. 40) DTCs P1130, P1150, P1131, P1151, P1132 Or P1152: Upstream HO2S Or Fuel System Not Switching

    DTCs P1131 and P1151 indicate air/fuel ratio is correcting rich for an overly lean condition. DTCs P1132 and P1152 indicate air/fuel ratio is correcting lean for an overly rich condition. DTCs P1130 and P1150 indicate when an HO2S fails to switch due to a circuit or fuel exceeding a calibrated limit. Possible causes are:

    • Fuel System

      Excessive fuel pressure, leaking or contaminated fuel injectors, leaking fuel pressure regulator, low fuel pressure or engine running out of fuel or vapory recovery system fault.

    • Induction System

      Air leaks after MAF sensor, air intake system obstructions, vacuum leaks, PCV system or improperly seated engine oil dipstick.

    • EGR System

      Leaking gasket, stuck EGR valve or leaking diaphragm or EVR.

    • Engine Mechanical

      Engine oil overfilled, cam timing, cylinder compression or exhaust leaks before or near HO2S.

    Inspect engine for obvious defects in specified systems. Repair as necessary. If no faults are found, go to TEST DC, step  25).

  17. 41) Continuous Memory DTC P0171, P0172, P0174 Or P0175: Fuel System At Corrected Fuel Trim

    DTCs P0171, P0172, P0174 and P0175 indicate a problem when adaptive fuel strategy senses a lean or rich condition beyond the minimum or maximum calibrated limit. Possible causes for these faults are:

    • Fuel System

      Excessive fuel pressure, leaking or contaminated fuel injectors, leaking fuel pressure regulator, low fuel pressure or engine running out of fuel or vapory recovery system fault.

    • Induction System

      Air leaks after MAF sensor, air intake system obstructions, vacuum leaks, PCV system or improperly seated engine oil dipstick.

    • EGR System

      Leaking gasket, stuck EGR valve or leaking diaphragm or EVR.

    • Engine Mechanical

      Engine oil overfilled, cam timing, cylinder compression or exhaust leaks before or near HO2S.

    Inspect engine for obvious defects in specified systems. Repair as necessary. If no faults are found, go to TEST DC, step  25).

  18. 42) Perform KOER Self-Test

    Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Disconnect fuel vapor hose from intake manifold and plug fitting at intake manifold. Start engine, and operate at 2000 RPM for 5 minutes, then allow to return to idle. Perform KOER ON-DEMAND SELF-TEST  and proceed as follows:
    • If DTCs P1127, P1128 or P1129 are present, go to appropriate system test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
    • If DTC (P1130, P1131) or (P1150, P1151) is present, go to next step.
    • If DTC (P1130, P1132) or (P1150, P1152) is present, go to step  49).

    If none of these DTCs are present, proceed as follows:

    • If Continuous Memory DTC P1130, P1150, P0171, P0172, P0174 or P0175 is present, go to step  52).
    • If DTCs P1132 and/or P1152 is no longer present, reconnect fuel vapor line.
    • If KOER DTCs 1131, 1132, 1151 and/or 1152 are present, perform evaporative system leakage tests. See EVAPORATIVE EMISSIONS DIAGNOSTIC TROUBLE CODE REFERENCE  under SYSTEM TESTS (EVAPORATIVE EMISSIONS).
    • On all others without reoccurring DTCs, fault is unable to be duplicated at this time. Go to TEST Z, step  1).

  19. 43) HO2S Circuit Test (With Lean DTCs)

    Disconnect suspect HO2S harness connector. Turn ignition switch to ON position. Using scan tool, select appropriate HO2S PID from PID/DATA MONITOR & RECORD menu. Connect a jumper wire between suspect HO2S harness connector HO2S SIG and VPWR terminals. If spark occurs when connecting jumper wire (indicating short circuit), remove jumper wire, check fuse in HO2S HTR circuit and go to step  47). If HO2S PID voltage is 1.3 volts or more, go to next step. If voltage is less than 1.3 volts, go to step  46).

  20. 44) Check SIG RTN Circuit For Open

    Turn ignition switch to OFF position. Using a DVOM, measure resistance of SIG RTN circuit between negative battery terminal and suspect HO2S harness connector terminal. See Fig 4. If resistance is less than 5 ohms, go to step  52). If resistance is 5 ohms or more, go to next step.

  21. 45) Check SIG RTN Circuit For Open

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Using a DVOM, measure resistance of SIG RTN circuit between PCM harness connector terminal and suspect HO2S harness connector terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure and Fig 4 . If resistance is less than 5 ohms, replace PCM. If resistance is 5 ohms or more, repair open in SIG RTN circuit.

  22. 46) Check HO2S SIG Circuit For Open

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Disconnect suspect HO2S harness connector. Inspect connectors for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance of HO2S SIG circuit between suspect HO2S harness connector terminal and appropriate PCM harness connector terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure and Fig 4 . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in SIG RTN circuit.

  23. 47) Check HO2S SIG Circuit For Short To Ground

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Ensure suspect HO2S harness connector is disconnected. Using a DVOM, measure resistance between PCM harness connector HO2S SIG and PWR GND terminals and HO2S SIG and HO2S SIG RTN terminals. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure. If both resistance measurements are more than 10 k/ohms, go to next step. If either resistance measurement is 10 k/ohms or less, repair short to ground in affected circuit.

  24. 48) Check HO2S For Short To Ground

    Reconnect suspect HO2S connector. Using a DVOM, measure resistance between PCM harness connector HO2S SIG and PWR GND terminals and HO2S SIG and HO2S SIG RTN terminals. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure. If both resistance measurements are 10 k/ohms or less, replace faulty HO2S. If both resistance measurements are more than 10 k/ohms, replace PCM.

  25. 49) Check HO2S Circuit (Rich DTCs)

    Ensure ignition switch is turned to OFF position. Disconnect suspect HO2S harness connector. Turn ignition switch to ON position. Using scan tool, select appropriate HO2S PID from PID/DATA MONITOR & RECORD menu. If HO2S PID voltage is more than .2 volt, go to next step. If HO2S PID voltage is .2 volt or less, go to step  51).

  26. 50) Check HO2S SIG Circuit For Short To VPWR & HO2S HTR Circuits

    Turn ignition switch to OFF position. Disconnect scan tool from DLC. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance between PCM harness connector suspect HO2S SIG and VPWR terminals, and HO2S SIG and HO2S HTR terminals. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure. If both resistance measurements are more than 10 k/ohms, replace PCM. If either resistance measurement is 10 k/ohms or less, repair short to HO2S HTR or VPWR circuit.

  27. 51) Check HO2S SIG For Short To HO2S HTR Circuit In Sensor

    With suspect HO2S harness connector disconnected. Using a DVOM, measure resistance between suspect HO2S connector HO2S SIG and HO2S HTR terminals. See Fig 4. If resistance measurement is more than 10 k/ohms, go to next step. If resistance measurement is 10 k/ohms or less, replace HO2S.
    28. NOTE: Fuel pump will only operate for 8 seconds when OUTPUT TEST MODE is activated.

  28. 52) Check Fuel Pressure
    Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM in appropriate REMOVAL, OVERHAUL & INSTALLATION article. Install fuel pressure gauge. Using scan tool, access OUTPUT TEST MODE. See OUTPUT TEST MODE  under ADDITIONAL SYSTEM FUNCTIONS. Command fuel pump ON. Record fuel pressure. See FUEL PRESSURE SPECIFICATIONS  table. If fuel system pressure is not as specified, go to TEST HC, step  1). If fuel system pressure is as specified, go to next step for vehicles with returnable fuel system, or go to step  55) for vehicles with returnless fuel system. See FUEL SYSTEM IDENTIFICATION  table.
    FUEL SYSTEM IDENTIFICATION

    Application Fuel System
    B2300, B2500, B3000, B4000 & Tribute 3.0L Mechanical Returnless
    Tribute 2.0L Electronic Returnless

  29. 53) Check Fuel System For Pressure Stability

    With fuel pressure gauge installed, cycle ignition from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). Check for external leaks and repair as necessary. If fuel pressure does not remain within 5 psi (34 kPa) of maximum pressure after one minute, go to TEST HC, step  5). If fuel pressure remains within 5 psi (34 kPa) of maximum pressure measurement for one minute, proceed as follows:
    • For Continuous Memory DTCs P1130, P1150, P0171, P0172, P0174 and P0175, go to next step.
    • For HO2S DTCs displayed with misfire DTCs, go to step  56).
    • For all other DTCs, go to step  59).

  30. 54) Check Fuel System For Pressure Stability With Ignition ON

    With fuel pressure gauge installed, cycle ignition from OFF to ON position 3-4 times to pressurize fuel system (DO NOT start engine). Note fuel pressure with ignition switch turned to ON position. If fuel pressure remains within 5 psi (34 kPa) of maximum pressure after 10 seconds, go to next step. If fuel pressure drops more than 5 psi (34 kPa) of maximum pressure after 10 seconds, go to next step.

  31. 55) Check Injector Fault PIDs & Associated DTCs

    Turn ignition switch to ON position. Using scan tool, select INJ1F-INJ10F PIDs from PID/DATA MONITOR & RECORD menu. If misfire DTCs are present, only select injector fault PIDs that correspond to misfire DTCs. If DTCs P0201-P0212 or PID values indicate an injector fault, go to next step. If DTCs P0201-P0212 are not present, PID values do not indicate an injector fault or any DTCs P0300-P0310 are present, go to TEST HD, step  12). If DTCs P0201-P0212 are not present, PID values do not indicate an injector fault or any other DTC is present, go to step  59).
    32. NOTE: Performing this test step will erase Continuous Memory DTCs.

  32. 56) Check Fuel Injector & Circuit Resistance
    Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure and record resistance between PCM harness connector VPWR and suspect fuel injector circuit terminals. See PCM FUEL INJECTOR, PWR GND & VPWR TERMINAL IDENTIFICATION  table. See Figure. Use injector fault PID noted in step  55) to determine fuel injector circuits that require testing. Resistance should be 11-18 ohms. If resistance is not as specified, go to next step. If resistance is as specified, replace PCM.
    PCM FUEL INJECTOR, PWR GND & VPWR TERMINAL IDENTIFICATION

    Application PCM Terminal No.
    Injector No. 1 75
    Injector No. 2 101
    Injector No. 3 74
    Injector No. 4 100
    Injector No. 5 (1) 73
    Injector No. 6 (1) 99
    Injector No. 7 (1) 72
    Injector No. 8 (1) 98
    Injector No. 9 (1) 68
    Injector No. 10 (1) 42
    PWR GND 51, 77 & 103
    VPWR 71 & 97
    (1) If applicable.

  33. 57) Check Fuel Injector Resistance

    Turn ignition switch to OFF position. Disconnect suspect fuel injector harness connector. Using a DVOM, measure resistance of fuel injector SIG and VPWR circuits between PCM harness connector terminals and suspect fuel injector harness connector terminals. See PCM FUEL INJECTOR, PWR GND & VPWR TERMINAL IDENTIFICATION  table. See Figure and Fig 5 . If both resistance measurements are less than 5 ohms, go to next step. If either resistance measurement is 5 ohms or more, repair open in fuel injector SIG or VPWR circuit.
    Fig 5: Identifying Fuel Injector Connector Terminals
    G99D02109Courtesy of FORD MOTOR CO.

  34. 58) Check Fuel Injector SIG Circuit For Short To PWR GND Or VPWR Circuits

    Turn ignition switch to OFF position. Disconnect PCM harness connector(s). Ensure suspect fuel injector harness connector is disconnected. Using a DVOM, measure resistance between PCM harness connector fuel injector SIG and VPWR terminals, and fuel injector SIG and PWR GND terminals. See PCM FUEL INJECTOR, PWR GND & VPWR TERMINAL IDENTIFICATION  table. See Figure. If each resistance measurement is more than 10 k/ohms, go to next step. If either resistance measurement is 10 k/ohms or less, repair short to PWR GND or VPWR circuit.

  35. 59) Flow Test Fuel Injector(s)

    Turn ignition switch to OFF position. Reconnect PCM and fuel injector connector(s). Use Rotunda fuel injector tester from Fuel Tester Kit (113-00114) to flow test fuel injectors. Follow injector tester instructions. If fuel injector flow or leakage rate is not okay, replace defective fuel injector(s). If flow rate for each fuel injector is okay, proceed as follows:
    • For DTCs P1131 and P1151, go to next step.
    • For DTCs P0171, P0174, P1130, and P1150, go to step  61).
    • For DTCs P1132 and P1152, go to step  64).
    • For DTCs P0172 and P0175, fault is unable to be duplicated at this time. Go to TEST Z, step  1).

  36. 60) Check For Secondary Air Intrusion

    If vehicle is not equipped with secondary air injection, go to next step. Possible causes for an HO2S always lean condition are:
    • Leak In Secondary Air Injection Pump Hoses
    • Secondary Air Diverted Upstream Of HO2S

    Turn ignition switch to OFF position. Disconnect secondary air injection hoses from engine and plug air injection ports (engine side). With engine at operating temperature, perform KOER ON-DEMAND SELF-TEST . If DTC P1131 or P1151 is present, reconnect air injection hoses and go to next step. If DTCs P1131 or P1151 are not present, check secondary air injection system. See TEST HM, step  7).

  37. 61) Check Air Induction System For Air Leaks

    Check inlet tubes from air cleaner to throttle body for leaks. Check PCV system for leaks. Check vacuum hoses for damage and tight connections. Check intake manifold gaskets. If any faults are found, repair as necessary. If no faults are found, proceed as follows:
    • For Continuous Memory DTCs P0171, P0174, P1130 or P1150, fault is unable to be duplicated at this time. Go to TEST Z, step  1).
    • For DTCs P1131 and P1130, or P1151 and P1150, go to next step.

  38. 62) Check Cylinder Compression

    Use Misfire DTCs retrieved in step  55) to determine which cylinder compression is suspect. Using compression gauge, check compression on all cylinders. Note suspect cylinder compression. Cylinder compressions should be higher than 75 percent of highest cylinder compression reading. If suspect cylinder compression is not within specification, repair engine as necessary. If suspect cylinder compression is within specification, go to next step if directed here for DTCs P1130, P1131, P1150 and P1151, or step  64) if directed here for DTCs P1132 and P1152. If misfire DTCs were displayed with fuel control DTCs, go to TEST HD, step  20).

  39. 63) Check HO2S Ability To Generate Voltage More Than .5 Volt

    Vacuum or air leaks can cause DTCs P1130, P1131, P1150, and P1151. Possible causes are:
    • Water Contamination In Connector
    • Leaking Vacuum Actuators
    • Engine Sealing Problems (Intake & IAC Valve)
    • Faulty EGR Valve
    • Faulty PCV System
    • Unmetered Air Leaks Between Throttle Body & MAF Sensor

    Turn ignition switch to OFF position. Inspect HO2S wiring harness for chafing, burned wires or other damage. Repair as necessary. Disconnect suspect HO2S connector. Connect DVOM between suspect HO2S connector HO2S SIG and SIG RTN terminals. Start engine and operate at 2000 RPM for 3 minutes. Perform KOER ON-DEMAND SELF-TEST  while monitoring HO2S voltage. If HO2S voltage is more than .5 volt during or at end of test, go to step  70). If voltage is .5 volt or less, replace faulty HO2S.

  40. 64) Attempt To Generate DTC P1131 Or P1151

    Start engine, and warm it to normal operating temperature. Turn ignition switch to OFF position. Disconnect suspect HO2S harness connector. Connect a jumper wire between suspect HO2S harness connector HO2S SIG terminal and negative battery terminal. Perform KOER ON-DEMAND SELF-TEST . If DTC P1131 or P1151 is present, turn ignition switch to OFF position, remove jumper wire and go to next step. If DTC P1131 or P1151 is not present, turn ignition switch to OFF position, remove jumper wire and reconnect HO2S harness connector. Disconnect and check PCM harness connector(s) for damaged or pushed out terminals, moisture or corrosion and repair as necessary. If PCM connector(s) is okay, replace PCM.

  41. 65) HO2S Sensor Voltage Check

    Leave HO2S disconnected. Connect DVOM between suspect HO2S connector HO2S SIG and SIG RTN terminals. Disconnect any vacuum hose from vacuum tree (simulate lean condition). Start engine and operate at 2000 RPM. If DVOM reads less than .4 volt within 30 seconds, turn ignition switch to OFF position, reconnect vacuum hose and HO2S and go to step  70). If DVOM reads .4 volt or more after 30 seconds, replace HO2S and repeat KOER ON-DEMAND SELF-TEST . If DTCs P1132 or P1152 are still present, replace PCM.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 65) to step 70). No test procedures have been omitted.

  42. 70) Monitor HO2S PID For Proper Switching During Wiggle Test

    Connect scan tool to Data Link Connector (DLC). Start engine and allow to idle. Ensure engine is at normal operating temperature. Using scan tool, select suspect HO2S PID from PID/DATA MONITOR & RECORD menu. Monitor suspect HO2S PID value while wiggling and bending small sections of wiring harness between suspect HO2S and PCM. If suspect HO2S PID voltage stays high (more than .45 volt) or stays low (less than .45 volt), isolate fault and repair as necessary. If suspect HO2S PID voltage switches, go to next step.

  43. 71) Monitor HO2S PID Switching During Test Drive

    Using an assistant, test drive vehicle under various conditions while observing suspect HO2S PID. If suspect HO2S PID voltage switches from more than .45 volts DC and then to less than .45 volts DC at least once every 3 seconds, system is okay at this time and testing is complete. If voltage does not switch from more than .45 volts DC and then to less than .45 volts DC at least once every 3 seconds, replace HO2S.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 71) to step 80). No test procedures have been omitted.

  44. 80) DTC P0136, P0156, P1137, P1138, P1157 & P1158

    Continuous Memory DTCs P0136 and P0156 indicate output voltage of downstream HO2S is not within calibrated limits. KOER DTCs P1137 or P1157 indicate PCM does not detect output of HO2S in a calibrated amount of time (lean condition). DTCs P1138 or P1158 indicate PCM does not detect output of HO2S in a calibrated amount of time (rich condition). DTCs P0136, P1137 and P1138 are for HO2S-12. DTCs P0156, P1157 and P1158 are for HO2S-22. See Fig 1-Fig 3 . Possible causes are:
    • Damaged Wiring Harness Or Connector
    • Crossed Sensor Wires
    • Exhaust System Leaks
    • Contaminated Or Faulty HO2S

    Service any Continuous Memory ignition and misfire DTCs before continuing. If no Continuous Memory ignition or misfire DTCs are present, check appropriate items in possible causes list in this step. Repair as necessary. If no faults are found, go to next step for DTCs P0136 and P0156, or step  82) for DTCs P1137, P1138, P1157 and P1158.

  45. 81) Check For KOER DTCs P1137, P1138, P1157 Or P1158

    Start engine, and operate at 2000 RPM for 3 minutes. Perform KOER ON-DEMAND SELF-TEST . If DTC P1137, P1138, P1157 or P1158 is present, go to next step. If DTCs P0136 or P0156 are present, fault is unable to be duplicated at this time. Go to TEST Z, step  1).

  46. 82) Check Exhaust System For Leaks

    DTCs P0136 and P0156 can be set when leaks exist in exhaust system between engine and rear of catalytic converter. Possible causes are:
    • Incorrect HO2S Torque
    • Exhaust System Leaks
    • Punctures Or Cracks In Pipes Leading To Or In Catalytic Converter

    Inspect exhaust system including catalytic converter and HO2S. Repair as necessary. If exhaust system is okay, go to next step.

  47. 83) Check HO2S SIG Circuit For Short To VPWR Or Ground Circuits

    Turn ignition switch to OFF position. Ensure suspect HO2S is disconnected. Disconnect scan tool from DLC. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance between PCM harness connector suspect HO2S SIG circuit terminal and PWR GND and SIG RTN circuit terminals. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure.

    Using a DVOM, measure resistance between PCM harness connector suspect HO2S SIG circuit terminal and VPWR and VREF circuit terminals. If all resistance measurements are more than 10 k/ohms, go to next step. If any resistance measurements are 10 k/ohms or less, repair short between HO2S SIG and PWR GND, SIG RTN, VPWR or VREF circuit.

  48. 84) Check HO2S SIG & SIG RTN Circuits For Open

    Using a DVOM, measure resistance of HO2S SIG circuit between suspect HO2S harness connector terminal and appropriate PCM harness connector terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure and Fig 4 . Using a DVOM, measure resistance of SIG RTN circuit between suspect HO2S harness connector terminal and appropriate PCM harness connector terminal. If both resistance measurements are less than 5 ohms, go to next step. If either resistance measurement is 5 ohms or more, repair open in HO2S SIG or SIG RTN circuit.

  49. 85) Check HO2S Circuit Voltage

    Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Reconnect suspect HO2S and PCM harness connectors. Turn ignition switch to ON position. Using scan tool, select suspect HO2S PID from PID/DATA MONITOR & RECORD menu. HO2S DTC identification is as follows:
    • DTCs P0136, P1137 and P1138 are for HO2S-12.
    • DTCs P0156, P1157 and P1158 are for HO2S-22.

    Refer to illustrations for HO2S identification. See Fig 1-Fig 3 . If HO2S PID voltage is more than 1.5 volts, go to step  88). If HO2S PID voltage is 1.5 volts or less, go to next step.

  50. 86) Check HO2S Ground Circuit In PCM

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Using a DVOM, measure resistance between PCM harness connector PWR GND and SIG RTN terminals. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure. If resistance measurement is less than 5 ohms, go to next step. If resistance measurement is 5 ohms or more, replace PCM.

  51. 87) HO2S Circuit Check

    Ensure ignition switch is turned to OFF position. Reconnect scan tool to Data Link Connector (DLC) and PCM harness connector(s). Connect a jumper wire between suspect HO2S harness connector VPWR and HO2S SIG terminals. See Fig 4. Turn ignition switch to ON position. Using scan tool, select suspect HO2S PID from PID/DATA MONITOR & RECORD menu. If suspect HO2S PID voltage is more than 1.5 volts, replace faulty HO2S. If suspect HO2S PID voltage is 1.5 volts or less, replace PCM.

  52. 88) Check For Over Voltage On HO2S Circuit In PCM

    With ignition switch turned to OFF position, disconnect suspect HO2S harness connector. Turn ignition switch to ON position. Using a DVOM, measure voltage between negative battery terminal and suspect HO2S harness connector HO2S SIG and SIG RTN terminals. See Fig 4. If either voltage measurement is more than 1.5 volts, replace PCM. If both voltage measurements are 1.5 volts or less, replace HO2S.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 88) to step 100). No test procedures have been omitted.

  53. 100) KOER DTC P1127

    DTC P1127 indicates that downstream HO2S heaters were not cycled on during KOER self-test due to exhaust temperatures falling below a minimum calibrated value. Possible causes are:
    • Engine Not At Operating Temperature
    • Exhaust System Too Cool

    Connect scan tool to Data Link Connector (DLC). Using scan tool, access all HO2S HTR PIDs from PID/DATA MONITOR & RECORD menu. If all HO2S HTR PIDs switch or indicate ON, perform KOER ON-DEMAND SELF-TEST . If any HO2S HTR PIDs do not switch or indicate OFF, operate engine until all HO2S HTR PIDs switch or indicate ON. Repeat KOER ON-DEMAND SELF-TEST .

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 100) to step 110). No test procedures have been omitted.

  54. 110) KOER DTCs P1128 & P1129

    These DTCs indicate that during KOER self-test, one or both HO2S signals were crossed from bank to bank. DTC P1128 refers to HO2S-11 or HO2S-21 in front of converter. DTC P1129 refers to HO2S-12 or HO2S-22 behind converter. Possible causes for these faults are:
    • Crossed HO2S Connectors
    • Crossed HO2S Wiring At HO2S Connector
    • Crossed HO2S Wiring At PCM Connector

    Turn ignition switch to OFF position. Disconnect suspect HO2S harness connector. Inspect connector for indication of crossed wires or incorrect installation. Repair as necessary. If no faults are found, go to next step.

  55. 111) Verify Proper HO2S SIG Terminal Location

    Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Disconnect both suspect HO2S harness connectors. HO2S DTC identification is as follows:
    • DTC P1128 is for upstream HO2S-11 and HO2S-21.
    • DTC P1129 is for downstream HO2S-12 and HO2S-22.

    Refer to illustrations for HO2S identification. See Fig 1-Fig 3 . Using a DVOM, measure resistance of HO2S SIG circuit between suspect HO2S harness connector and appropriate PCM harness connector terminal. See PCM HO2S, VPWR & GROUND TERMINAL IDENTIFICATION  table. See Figure and Fig 4 . If resistance is less than 5 ohms, fault is intermittent and cannot be duplicated at this time. Go to TEST Z, step  1). If resistance is 5 ohms or more, HO2S wiring is crossed. Recheck all HO2S wiring terminal locations at PCM and HO2S connectors. Repair as necessary.

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