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Diagnostic Aids

Delayed engagement of transmission may be caused by mechanical malfunction. Harsh shifts and/or erratic speedometer measurement may be caused by a failed speedometer or an open or intermittent ground within the instrument panel (electronic instrument cluster).

Perform this test when directed by QUICK TEST. This system test is intended to diagnose:

  1. 1) Continuous Memory DTC P0500, P0501 Or P1502: Check VSS Circuits For Open (VRS Type)

    DTCs P0500, P0501 and P1502 indicate that PCM has detected an error in vehicle speed information received from Vehicle Speed Sensor (VSS), Transfer Case Speed Sensor (TCSS), Anti-Lock Brake System (ABS) module, Generic Electronic Module (GEM) or Central Timer Module (CTM). See MODULE IDENTIFICATION  table. Possible causes for this fault are:
    • Open Or Short In VSS (+) Or VSS (-) Circuit
    • Open In TCSS Signal Or TCSS Signal Return Circuit
    • Short To GND In VSS Or TCSS Circuit
    • Short To PWR In VSS Or TCSS Circuit
    • Open Or Short In VSC Between PCM & Appropriate Control Module
    • Faulty Drive Mechanism For VSS Or TCSS
    • Faulty Module(s) Connected To Vehicle Speed Circuit
    • Faulty Transfer Case, Vehicle Or Wheel Speed Sensors

    Turn ignition switch to OFF position. Disconnect VSS. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance of VSS(+) circuit between PCM harness connector terminal and VSS harness connector terminal. Using a DVOM, measure resistance of and VSS(-) circuit between PCM harness connector terminal and VSS harness connector terminal. See Fig 1 or Fig 2 . 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 VSS circuit.

    Fig 1: Identifying VSS Circuits & Connector Terminals (Except Tribute M/T)
    G99H02106Courtesy of FORD MOTOR CO.
    Fig 2: Identifying TCSS Circuits & Connector Terminals (Tribute M/T)
    G00035649Courtesy of FORD MOTOR CO.

  2. 2) Check VSS Circuits For Shorts To Ground Or Power

    Using a DVOM, measure resistance between PCM harness connector VSS(+) terminal and PWR GND, VPWR and VSS(-) terminals. See WIRING DIAGRAMS article. See Fig 1 or Fig 2 . If all resistance measurements are more than 5 ohms, go to next step. If any resistance measurement is 5 ohms or less, go to step  12).

  3. 3) Check VSS Resistance

    Using a DVOM, measure resistance between VSS terminals. If resistance is not 170-270 ohms, replace VSS. If resistance is 170-270 ohms, replace PCM.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 5). No test procedures have been omitted.

  4. 5) Continuous Memory DTC P0500, P0501 Or P1502: Check VSS Circuits For Open (Hall Type)

    DTCs P0500, P0501 and P1502 indicate that PCM has detected an error in vehicle speed information received from Vehicle Speed Sensor (VSS), Transfer Case Speed Sensor (TCSS), Anti-Lock Brake System (ABS) module, Generic Electronic Module (GEM) or Central Timer Module (CTM). See MODULE IDENTIFICATION  table. Possible causes for this fault are:
    • Open Or Short In VSS (+) Or VSS (-) Circuit
    • Open In TCSS Signal Or TCSS Signal Return Circuit
    • Short To GND In VSS Or TCSS Circuit
    • Short To PWR In VSS Or TCSS Circuit
    • Open Or Short In VSC Between PCM & Appropriate Control Module
    • Faulty Drive Mechanism For VSS Or TCSS
    • Faulty Module(s) Connected To Vehicle Speed Circuit
    • Faulty Transfer Case, Vehicle Or Wheel Speed Sensors

    Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Raise and support front of vehicle (to allow rotation of front drive wheel). Opposite front wheel must be stationary. Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector VSS and PWR GND terminals while slowly rotating drive wheel. See Figure. Voltage should fluctuate from less than one volt to more than 5 volts as drive wheel is rotated. If voltage is as specified, replace PCM. If voltage is not as specified, go to next step.

  5. 6) Check VPWR To VSS

    Turn ignition switch to OFF position. Disconnect VSS connector. Turn ignition switch to ON position. Using a DVOM, measure voltage between VSS harness connector VPWR and PWR GND terminals. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, go to step  10).

  6. 7) Check VSS Circuit For Short To Power

    Turn ignition switch to ON position. Using a DVOM, measure voltage between PCM harness connector VSS(+) and PWR GND terminals. See Figure. If voltage is less than one volt, go to next step. If voltage is one volt or more, go to step  12).

  7. 8) Check VSS Circuit For Short To Ground

    Turn ignition switch to OFF position. Using a DVOM, measure resistance between PCM harness connector VSS(+) and PWR GND terminals. If resistance is more than 3000 ohms, go to next step. If resistance is 3000 ohms or less, go to step  12).

  8. 9) Check VSS Signal Circuit For Open

    Using a DVOM, measure resistance of VSS circuit between PCM harness connector terminal and VSS harness connector terminal. If resistance is less than 5 ohms, replace VSS. If resistance is 5 ohms or more, repair open in VSS circuit.

  9. 10) Check VSS Ground Circuit For Open

    Turn ignition switch to OFF position. Ensure PCM and VSS are disconnected. Using a DVOM, measure resistance of PWR GND circuit between negative battery terminal and VSS harness connector terminal. If resistance is less than 5 ohms, repair open in VPWR circuit to VSS. If resistance is 5 ohms or more, repair open in VSS PWR GND circuit.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 12). No test procedures have been omitted.

  10. 12) Verify If VSS Circuit Is Shorted In Wiring Harness Or Another Module

    Determine if any other modules are connected to VSS circuit. See WIRING DIAGRAMS article. If no other modules are connected to vehicle speed circuit, repair short in PWR GND, VPWR or VSS(-) circuit. If other modules are connected to vehicle speed circuit, disconnect each module(s) (one at a time) that are associated with VSS circuit. After disconnecting each module, check again for short circuit. Refer to test step that directed you to this step. Repeat until each associated module has been disconnected or short circuit has been eliminated. If short circuit no longer exists with associated module(s) disconnected, diagnose appropriate module and/or related system. See appropriate MODULE COMMUNICATIONS NETWORK article in ACCESSORIES & EQUIPMENT. If short circuit still exists with all associated modules disconnected, repair short in VSS circuit.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 15). No test procedures have been omitted.

  11. 15) KOER DTC P1501: Check PCM VSS PID For Input Signal

    This DTC indicates VSS input signal is out of self-test range. A DTC P1501 will be set and self-test will abort whenever PCM detects VSS input signal during KOER ON-DEMAND SELF-TEST. A noisy VSS input signal from Radio Frequency Interference (RFI) Or Electromagnetic Interference (EMI) external source (ignition wires, charging circuits, etc.) are possible causes for this fault.

    Connect scan tool to Data Link Connector (DLC). Start engine and allow to idle. Using scan tool, select VSS PID from PID/DATA MONITOR & RECORD menu and observe vehicle speed input to PCM. While observing VSS PID, increase engine speed to 2000 RPM and return to idle several times. If VSS PID measurement is 3 MPH or more, go to step  22). If VSS PID value is less than 3 MPH, fault cannot be duplicated at this time. Clear DTCs and repeat QUICK TEST . If DTC P1501 is still present, go to TEST Z, step  1).

    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.

  12. 20) Continuous Memory DTC P0503: Check For Intermittent Fault

    This DTC indicates poor or noisy VSS performance. Possible causes for this fault are:
    • Noisy VSS/TCSS Input Signal From RFI Or EMI External Source (Ignition Wires, Charging Circuits, Etc.)
    • Faulty VSS Or Driven Gears
    • Faulty TCSS
    • Damaged Circuit
    • Faulty VSS Gear(s)
    • Faulty Module Or Circuit Connected To TCSS/VSS
    • Aftermarket Add-On Accessories

    Turn ignition switch to OFF position. Disconnect VSS sensor. Visually inspect VSS and VSS circuits for potential faults as follows:

    • Loose VSS Circuit Connectors
    • Loose VSS Circuit Connector Terminals
    • Damaged VSS Wiring Harness Insulation
    • Incorrect VSS Circuit Routing
    • Incorrect VSS Installation

    If no faults are found, go to next step. If faults are found, repair as necessary.

  13. 21) Check PCM VSS PID For Input Signal

    Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Using scan tool, select VSS PID from PID/DATA MONITOR & RECORD menu. Test drive vehicle at several steady speeds at more than and less than 30 MPH.
    NOTE: On scan tools with Data Record feature, record data for playback to help identify variations.

    During each steady state speed, check for VSS PID variations of plus or minus 5 MPH for 10 seconds or more. If any variations occur, go to next step. If variations do not occur, fault cannot be duplicated at this time. Testing is complete.

  14. 22) Check VSS Wiring Harness Routing

    Visually inspect VSS wiring harness. Ensure wiring is not routed near high current wires such as ignition wires or alternator wires. Verify VSS wiring harness is shielded and grounded (if applicable). Check VSS wiring harness resistance. Refer to Fig 1 or Fig 2 to check VSS circuits. If faults are found, repair as necessary. If no faults are found, fault cannot be duplicated at this time. Go to TEST Z, step  1) and check for intermittents.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22) to step 25). No test procedures have been omitted.

  15. 25) Continuous Memory DTC P1500: Visual Inspection

    This DTC indicates PCM detected intermittent input from VSS while PCM performs OBD-II drive cycle monitoring procedures. Possible causes for this fault are:
    • Intermittent Open Or Shorted Circuit
    • Faulty VSS
    • Faulty PCM

    Turn ignition switch to OFF position. Disconnect VSS sensor. Visually inspect VSS and VSS circuits for potential faults as follows:

    • Loose VSS Circuit Connectors
    • Loose VSS Circuit Connector Terminals
    • Damaged VSS Wiring Harness Insulation
    • Incorrect VSS Circuit Routing
    • Incorrect VSS Installation

    If no faults are found, go to TEST Z, step  1). If faults are found, repair as necessary.

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 30). No test procedures have been omitted.

  16. 30) Continuous Memory DTC P0500 Or P1502: Visual Inspection

    Transfer Case Speed Sensor (TCSS) provides rotational speed of transfer case output shaft. This signal is used on some models as source of vehicle speed information. Disconnect TCSS 2-pin connector, located on left rear of transmission. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. If connector terminals are okay, go to next step.

  17. 31) Check TCSS Resistance

    Using a DVOM, measure resistance between TCSS terminals. If resistance is 1000-1250 ohms, go to next step. If resistance is not 1000-1250 ohms, replace TCSS.

  18. 32) TCSS Output Check

    Road test vehicle and measure frequency between TCSS terminals. Drive vehicle at 30 MPH. Compare TCSS frequency to the frequency listed in PIN VOLTAGE/PID VALUE - INPUTS table in PIN VOLTAGE/PID VALUE CHARTS article. Ensure frequency increases and decreases with vehicle speed. If frequency is as specified, go to next step. If frequency is not as specified, remove TCSS from transmission. Inspect TCSS target wheel and repair as necessary. If TCSS target wheel is okay, replace TCSS.

  19. 33) Check For Short To Power

    Turn ignition switch to ON position. Ensure TCSS is disconnected. Using a DVOM, measure voltage between chassis ground and TCSS harness connector TCSS signal terminal. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short to VPWR.

  20. 34) Check Wiring Harness For Open Circuit

    Turn ignition switch to OFF position. Disconnect PCM connector. Using a DVOM, measure resistance of TCSS signal circuit between TCSS harness connector terminal and PCM harness connector terminal. Using a DVOM, measure resistance of TCSS SIG RTN circuit between TCSS harness connector terminal and 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 affected circuit.

  21. 35) Check Wiring Harness For Short To Ground

    Using a DVOM, measure resistance between TCSS harness connector TCSS SIG RTN and TCSS signal terminals. Using a DVOM, measure resistance between chassis ground and TCSS harness connector TCSS signal terminal. 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 ground in TCSS signal circuit.
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