Diagnostic Aids

Perform this test only when directed by QUICK TEST . This test is intended to diagnose the following:

• Wiring harness circuits (VSC SIG and VSC GND).
• Powertrain Control Module (PCM).

Fig 1: ABS Module VSC Connector Terminals

1. Step 1) DTC P0500: Check Vehicle Speed PID  DTC P0500 indicates that PCM has detected error in vehicle speed information received from ABS module. Possible causes for this fault are:
   • Open or short in harness.
   • Faulty ABS module.
   • Faulty Powertrain Control Module (PCM).

   Turn ignition off. Connect scan tester to Diagnostic Link Connector (DLC). Turn ignition on. Using scan tester, access VSS PID. Road test vehicle as follows:

   • Gradually accelerate vehicle to 50 MPH while observing VVV PID MPH.

   If VSS PID matches speedometer, fault is intermittent; go to step 4). If VSS PID does not match speedometer, go to next step.

2. Step 2) Check Circuit Continuity  Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (014-00950), leaving PCM disconnected. Disconnect ABS wiring harness connector. Measure resistance between VSC GND terminal of ABS module wiring harness connector and test pin No. 33 at breakout box. Measure resistance between VSC SIG terminal of ABS module wiring harness connector and test pin No. 58 at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit, and repeat QUICK TEST .
3. Step 3) Check Circuit For Short To Ground  Leave PCM and ABS module disconnected. Disconnect scan tester from DLC (if applicable). Turn ignition off. Measure resistance between test pin No. 58 and test pins No. 33 (VSC GND), 51 and 103 (PWR GND) No. 71 (VPWR) and No. 91 (SIG RTN). Measure resistance between test pin No. 33 and test pin No. 71. If any reading is less than 10,000 ohms, repair short circuit, and go to step 5). If all readings are 10,000 ohms or more, check for fault in ABS system. If no faults are present, replace PCM.
4. Step 4) Visual Inspection  Turn ignition off. Visually inspect VSC wiring harness for any of the following conditions:
   • Loose or corroded ABS module connector.
   • Loose or corroded PCM connector.
   • Incorrect routing of VSC wiring harness.

   If any faults are present, repair as necessary and go to next step. If all readings are 10,000 ohms or more, check for fault in ABS system.

5. Step 5) Test Drive Vehicle  Ensure engine is warmed to normal operating temperature. Perform the following drive cycle 3 times:

   A/T Equipped Vehicles

   • Place gear selector in Drive.
   • Accelerate heavily to 35 MPH.
   • Coast down to idle speed and stop vehicle.

   M/T Equipped Vehicles

   • Place gear selector in first gear.
   • Accelerate heavily to 35 MPH, not shifting higher than second gear.
   • Coast down to idle speed and stop vehicle.

   After third drive cycle, perform QUICK TEST . If any DTCs are present, go to appropriate CIRCUIT TEST. If DTCs are not present, testing is complete.