Diagnostic Aids

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

• PSOM output to PCM.
• PSOM (+) and PSOM (-) wiring harness circuits.
• PCM.

To prevent replacement of good components, be aware following non EEC related areas and components may be cause of problem:

• Cruise Control system.
• Rear Anti-Lock Brake System (RABS).
• Ring gear inside differential.
• Instrumentation system.

Fig 1: Programmable Speedometer/Odometer Module Circuit Logic

Fig 2: Programmable Speedometer/Odometer Module (PSOM) Circuit

1. Continuous Memory Code 29/452
   
   Code 29/452 indicates PCM detected incorrect output from VSS sometime during vehicle operation. Following are possible causes of code.
   • PSOM output to PCM.
   • PSOM (+) and PSOM (-) wiring harness circuits.
   • PCM.

   Turn ignition off. Remove PCM 60-pin connector. Inspect terminals, and repair if damaged. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pins No. 3 and 6 at breakout box. If reading is 21-55 k/ohms, go to step 4). If resistance is not 21-55 k/ohms, go to next step.

2. Check PSOM Circuit Continuity
   
   Ensure ignition is off. Disconnect PSOM wiring harness connector. Measure resistance between test pin No. 3 at breakout box and PSOM (+) circuit at PSOM wiring harness connector. Measure resistance between test pin No. 6 at breakout box and PSOM (-) circuit at PSOM wiring harness connector. If resistance is more than 5 ohms, repair open circuit and repeat QUICK TEST  . If resistance is 5 ohms or less, go to next step.
3. Check PSOM Circuit For Open
   
   Ensure ignition is off. Measure resistance between test pin No. 3 and test pins No. 6, 37 and 40 at breakout box. If resistance is 10 k/ohms or less, repair open circuit and repeat QUICK TEST  . If resistance is more than 10 k/ohms, go to next step.
4. Check RABS Sensor Resistance
   
   Turn ignition off. Remove RABS connector. See Figure . Measure resistance between connector terminals, If resistance is not 1300-1550 ohms, replace RABS and repeat QUICK TEST  . If resistance is 1300-1550, go to next step.
5. Check PSOM Output Voltage
   
   Turn ignition off. Connect PCM to breakout box. Connect wiring harness connector to PSOM. Set DVOM on 20-volt AC scale. Start engine, and warm to normal operating temperature. Using an assistant, measure voltage between test pins No. 3 and 6 while gradually increasing vehicle speed to 50 MPH. If maximum voltage is less than 4 volts, fault is in instrument cluster. If maximum voltage received is more than 4 volts, replace PCM.