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Diagnostic Aids

Delayed engagement of transmission may be caused by mechanical malfunction. Harsh shifts and/or erratic speedometer reading 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 CIRCUIT TEST is intended to diagnose:

Fig 1: VSS Circuit & Connector Terminals
G95F35951
  1. Step 1) DTC P0500  This code indicates PCM detected incorrect output from VSS sometime during vehicle operation. Possible causes for this code are:
    • Faulty VSS.
    • Open or shorted circuit.
    • Faulty PCM.

    Turn ignition off. Disconnect VSS sensor. Remove PCM 104-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pin No. 58 and VSS(+) terminal at VSS wiring harness connector. Measure resistance between test pin No. 33 and VSS(-) terminal at VSS wiring harness connector. If resistance readings are less than 5 ohms, go to next step. If either resistance reading is 5 ohms or more, repair open circuit in VSS wiring harness. Clear PCM memory and go to step 27).

  2. Step 2) Check VSS Circuits For Shorts To Power Or Ground  Turn ignition off. Ensure PCM and VSS are disconnected. Measure resistance as follows:
    • Between test pin No. 33 and test pin No. 58 and 71 (VPWR).
    • Between test pin No. 58 and test pins No. 24, 61, 76 and 103 (PWR GND).
    • Between test pin No. 58 and test pins No. 71 (VPWR) and 91 (SIG RTN).

    If all readings are more than 500 ohms, go to next step. If any reading is 500 ohms or less, repair short in wiring harness. Clear PCM memory and go to step 27).

  3. Step 3) Check VSS Resistance  Turn ignition off. Disconnect VSS wiring harness connector. Measure resistance between VSS terminals. If resistance is not 190-250 ohms, replace VSS and go to step 27). If resistance is 190-250 ohms, replace PCM and go to step 27).
    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. Step 5) DTC P0500  This code indicates PCM detected incorrect output from VSS sometime during vehicle operation. Possible causes for this code are:
    • Faulty VSS.
    • Open or shorted circuit.
    • Faulty PCM.

    Turn ignition off. Disconnect VSS sensor. Remove PCM 104-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Check voltage between test pins No. 58 and 103 at breakout box while slowly rotating drive wheels. If voltage fluctuates 1.0-5.0 volts as wheels are rotated, replace PCM and go to step 27). If voltage does not fluctuate 1.0-5.0 volts, go to next step.

  5. Step 6) Check VPWR To VSS  Turn ignition off. Disconnect VSS wiring harness connector. Turn ignition on. Measure voltage at connector as follows:
    • Between VPWR and PWR GND terminals.
    • Between VSS+ and VSS- terminals.

    If voltage is 10.5 volts or more, go to next step. If voltage is 10.5 volts or less, go to step 10).

  6. Step 7) Check VSS Circuits For Short To Power  Turn ignition off. Ensure PCM and VSS are disconnected. Measure voltage between test pins No. 58 and 103 at breakout box. If voltage is less than 1.0 volt, go to next step. If voltage is 1.0 volt or more, repair short to power and go to step 27).
  7. Step 8) Check VSS Circuits For Short To Ground  Turn ignition off. Ensure PCM and VSS are disconnected. Measure resistance between test pin No. 58 and 103 at breakout box. If resistance is more than 3000 ohms, go to next step. If resistance is 3000 ohms or less, repair short to ground and go to step 27).
  8. Step 9) Check VSS Circuit Continuity  Turn ignition off. Ensure PCM and VSS are disconnected. Measure resistance between test pin No. 58 and the VSS or VSS+ terminal at VSS wiring harness connector. If all resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit and go to step 27).
  9. Step 10) Check VSS Ground Circuit Continuity  Turn ignition off. Ensure PCM and VSS are disconnected. Measure resistance between chassis ground and PWR GND or VSS(-) terminal at VSS wiring harness connector. If resistance is less than 5 ohms, repair open in power circuit to VSS and go to step 27). If resistance is 5 ohms or more, repair open in ground circuit and go to step 27).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 15). No test procedures have been omitted.
  10. Step 15) KOER DTC P1500: Check PCM VSS PID For Input Signal  This code indicates VSS input signal is out of range. A DTC 1501 will be set and self-test will abort whenever PCM detects VSS input signal during KOER self-test. Possible causes for this code are:
    • Noisy VSS input signal from RFI/EMI external source (ignition wires, charging circuits etc.).

    Turn ignition off. Connect scan tester to DLC. Start engine and allow to idle. Using scan tester, access VSS PID and observe vehicle speed input to PCM. While observing VSS PID, increase engine speed to 2000 RPM and decrease to idle several times. If VSS PID reading is less than 3 MPH, fault cannot be duplicated at this time. Testing is complete. If VSS PID reading 3 MPH or more, go to step 22).

    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.
  11. Step 20) Continuous Memory P0503: Check For Intermittent Fault  This code indicates poor VSS performance. Possible causes for this code are:
    • Noisy VSS input signal from RFI/EMI external source (ignition wires, charging circuits etc.).
    • Damaged circuit.
    • Faulty VSS.
    • Faulty VSS gear(s).

    Turn ignition off. Disconnect VSS sensor. Visually inspect VSS and VSS circuits for potential faults as follows:

    • Loose VSS circuit connectors.
    • Loose VSS circuit connector pins.
    • 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 or replace as necessary. Clear PCM memory and go to step 27).

  12. Step 21) Check PCM VSS PID For Input Signal  Turn ignition off. Connect scan tester to DLC. Test drive vehicle, averaging 30 MPH. While driving at a steady speed, check for VSS PID variations of more than 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.
  13. Step 22) Visually inspect VSS wiring harness. Ensure wiring is not routed near ignition wires or alternator wires. Verify VSS wiring harness is shielded and grounded (if applicable). Repeat step 1) to verify circuit continuity. If faults are found, repair or replace as necessary. Clear PCM memory and go to step 27). If no faults are found, fault cannot be duplicated at this time. Testing is complete.
    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. @@ Step 25) DTC P1500  This code indicates PCM detected intermittent input from VSS. Possible causes for this code are:
    • Intermittent open or shorted circuit.
    • Faulty VSS.
    • Faulty PCM.

    Turn ignition off. Disconnect VSS sensor. Visually inspect VSS and VSS circuits for potential faults as follows:

    • Loose VSS circuit connectors.
    • Loose VSS circuit connector pins.
    • Damaged VSS wiring harness insulation.
    • Incorrect VSS circuit routing.
    • Incorrect VSS installation.

    If no faults found, go to CIRCUIT TEST Z. If faults found, repair or replace as necessary. Clear PCM memory and go to step 27).

    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 27). No test procedures have been omitted.
  14. Step 27) VSS Drive Cycle  Record and clear continuous memory codes. Warm engine to normal operating temperature. Perform appropriate drive cycle as follows:
    • On models with A/T, place gear selector in Drive position. Accelerate hard to 35 MPH and coast down to a stop. Repeat procedure 3 times. Shut off engine. Repeat QUICK TEST . Service codes as necessary. If no codes are present, testing is complete.
    • On models with M/T, start in first gear, shifting no higher than second gear. Accelerate moderately to 40 MPH. Coast down to idle, and stop. Repeat procedure 3 times. Shut engine off. Repeat QUICK TEST . Service codes as necessary. If no codes are present, testing is complete.
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