Diagnostic Aids

Perform this test when instructed during QUICK TEST  or if directed by other test procedure. This test is intended to diagnose the following:

• HO2S and heater.
• HO2S and sensor connection.
• Vacuum systems.
• Fuel injector and/or fuel injector circuitry.
• Powertrain Control Module (PCM).
• Harness circuits; HO2S, HO2SH, INJ 1-6 and VPWR.

Fig 1: Fuel Injector Circuits & Connector Terminals

Fig 2: Identifying HO2S Circuits

1. Step 1) DTC P0130 & P0136: HO2S Circuit Malfunction  DTCs P0130 and P0136 indicate an irrational value in upstream HO2S circuit. Possible causes for fault are as follows:
   • Damaged upstream HO2S or circuit.
   • Intake air system malfunction.
   • Fuel system malfunction.
   • Exhaust system leak.
   • Ignition system malfunction

   Turn ignition off. Connect NGS scan tool to OBD - II DLC. Start engine and run until engine is at normal operating temperature. Access HO2S PIDs. Run engine at different speeds while observing HO2S PID. If HO2S PID is not constantly varying between 0.4-1.0 volt (fixed or no voltage), go to step 11). If HO2S PID is 0.4-1.0 volt and constantly varying, HO2S is okay at this time. Go to CIRCUIT TEST Z or the TESTS W/O CODES article for intermittent diagnostic procedure.

   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 1) to step 11). No test procedures have been omitted.
2. Step 11) Check HO2S Output Voltage  Warm engine to normal operating temperature. Turn ignition off. Connect NGS scan tool to OBD-II DLC. Access HO2S PIDs. Start engine and run at 2000 RPM while observing HO2S PID. If HO2S reaches 0.6 volt or greater, go to step 14). If HO2S never reaches 0.6 volt, go to next step.
3. Step 12) Check HO2S Circuit Continuity  Turn ignition off. Disconnect suspect HO2S connector. Disconnect PCM connector. Inspect connector for damaged pins and repair if necessary. Install breakout box (leave PCM disconnected). Measure resistance between suspect HO2S harness connector and appropriate breakout box test pin (pin No. 26 or 78). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open HO2S circuit. Repeat QUICK TEST .
4. Step 13) Check HO2S Signal Short To Ground  Turn ignition off. Disconnect suspect HO2S sensor. Install breakout box (leave PCM disconnected). Measure resistance between breakout box test pin No. 26 or 78 and ground. If resistance less than 10,000 ohms repair short to ground in HO2S circuit. Repeat QUICK TEST . If resistance is greater than 10,000 ohms, go to step 40). If all systems are okay, go to step 15).
5. Step 14) Check For Short To Power  Turn ignition off. Disconnect suspect HO2S sensor. Install breakout box (leave PCM disconnected). Turn ignition on. Measure voltage between breakout box test pin No. 26 or 78 and ground. If one volt or more is present, repair short to power in HO2S circuit. If less than one volt is present, go to step 40). If all systems are okay, go to step 15).
6. Step 15) Erase DTCs  Erase DTCs from memory. See CLEARING CODES . Run engine at 1500-2000 RPM for at least 3 minutes. Repeat QUICK TEST . If DTC P0130 or P0136 returns, replace HO2S in question.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 15) to step 20). No test procedures have been omitted.
   NOTE: DTC P0135 indicates upstream HO2S heater circuit fault. DTC P0141 indicates downstream HO2S heater fault.
7. Step 20) DTC P0135 & P0141: Heater Circuit Malfunction  DTC P0135 and P0141 indicate a malfunction in HO2S heater circuit. Possible causes for malfunction are as follows:
   • Faulty or damaged HO2S.
   • Poor harness connection.
   • Open or short in heater circuit.
   • Open heater GND circuit.
   • Faulty PCM.

   Examine HO2S harness connectors for damage or corrosion etc. Repair connectors as necessary. If HO2S harness connectors are okay, go to next step.

8. Step 21) Check HO2S Heater PID  Turn ignition off. Connect NGS scan tool to OBD-II DLC. Access HO2SH PID. Start engine and run at 2000 RPM while observing PID data. If PID indicates ON for approximately 4 minutes after engine is started, go to step 23). If HO2SH PID indicates ON for longer than 4 minutes after engine is started, go to next step. If HO2SH PID does not indicate ON at all, go to step 23).
9. Step 22) Check HO2SH Circuit For Short To Ground  Turn ignition off. Disconnect suspect HO2S sensor. Install breakout box (leave PCM disconnected). Measure resistance between breakout box test pin No. 83 or 84 and ground. If resistance is less than 10,000 ohms, repair short to ground in sensor heater circuit. Repeat QUICK TEST . If resistance is greater than 10,000 ohms, go to next step.
10. Step 23) Check VPWR Circuit Continuity  Turn ignition off. Disconnect suspect HO2S sensor. Turn ignition on. Measure voltage at VPWR terminal at HO2S harness connector (Blue/Yellow wire) and ground. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open VPWR circuit. Restore all electrical connections and repeat QUICK TEST .
11. Step 24) Check HO2S Heater Circuit Continuity  Turn ignition off. Disconnect suspect HO2S sensor. Install breakout box (PCM disconnected). Measure resistance between HO2SH terminal at harness connector of suspect sensor and appropriate breakout box test pin (pin No. 83 or 84). If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open HO2SH circuit. Restore electrical connections repeat QUICK TEST .
12. Step 25) Check HO2S Heater  Turn ignition off. Disconnect suspect HO2S. Measure resistance between Blue/Yellow wire terminal and Black wire terminal (component side). If resistance is approximately 6 ohms, replace PCM. Restore electrical connections and repeat QUICK TEST . If resistance is not approximately 6 ohms, replace HO2S. Restore electrical connections and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 40). No test procedures have been omitted.
13. Step 40) DTC P0171 & P0172: Fuel Trim Malfunction  DTC P0171 indicates cylinder bank No. 1 air/fuel ratio too lean or rich. DTC P0172 indicates cylinder bank No. 2 air/fuel ratio too lean or rich. Possible causes for malfunction are as follows:
    • Excessive fuel pressure.
    • Leaking fuel injector(s).
    • Leaking fuel pressure regulator.
    • Low fuel pressure.
    • Restricted fuel injectors.
    • Faulty HO2S or circuit.
    • Induction system air leaks.
    • Restricted air filter.
    • Faulty PCV system.
    • Engine mechanical problem.
    • Oil level over full.
    • Ignition system malfunction.

    If any of the above areas are faulty, repair as necessary. If all of the above areas are okay, go to next step.

14. Step 41) Fuel Pressure Check  Connect fuel pressure gauge to fuel rail or fuel filter. Start engine and observe fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, go to CIRCUIT TEST HC.
15. Step 42) Check Fuel Pressure Leakdown  With fuel pressure gauge installed, turn ignition switch on and off several times. Turn ignition off and observe fuel pressure gauge. If fuel pressure drops less than 5 psi in one minute, go to next step. If fuel pressure drops 5 psi or more in one minute, check for external leaks. If no external leakage is found, check fuel injectors, fuel pressure regulator and fuel pump check valve for internal leakage. See CIRCUIT TEST HC.
16. Step 43) Check Injector Circuit Resistance  Turn ignition off. Disconnect negative battery cable. Disconnect PCM and inspect connector for corroded or pushed out pins etc, repair as necessary. Install breakout box (leave PCM disconnected). Measure resistance between breakout box test pin No. 67 (KAPWR) and fuel injector test pins. See Fig 1. If resistance is 10-14 ohms, circuit is okay, go to step 46). If resistance is not 12-16 ohms, go to next step.
17. Step 44) Check Injector Harness  Turn ignition off. Breakout box installed (PCM disconnected). Disconnect injector harness connectors. Measure resistance between breakout box test pin No. 67 (KAPWR) and KAPWR terminal at each injector harness connector. See Fig 1. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open harness circuit as necessary. Restore electrical connections and repeat QUICK TEST .
18. Step 45) Check Injector Harness For Short  Turn ignition off. Breakout box installed (PCM connected). Disconnect suspect injector harness connector. Measure resistance between breakout box test pins No. 67 (KAPWR) and 43 (GND) and 50 (SIG RTN). Measure resistance between injector signal pin and ground. If all resistance measurements are greater than 10,000 ohms, go to next step. If any resistance measurement is less than 10,000 ohms, repair shorted circuit. Restore all electrical connections and repeat QUICK TEST .
19. Step 46) Check Injector Driver  Turn ignition off. Breakout box installed (Connect PCM). Connect a standard non-powered test light between breakout box test pin No. 67 KAPWR and each injector test pin. See Fig 1. Crank engine. If test light dimly glows while cranking, remove breakout box and go to next step. If test light does not glow or glows brightly, replace PCM. Restore electrical connections and repeat QUICK TEST .
20. Step 47) Check Injector Flow  Using Rotunda Fuel Injector Tester Cleaner (164-R3759). Replace any injectors that are not within leakage and flow specification. If all injectors are within leakage and flow specification, fault is intermittent. See CIRCUIT TEST Z. Also check PIDs SHRTFT1, SHRTFT2, LONGFT1, LONGFT2.