Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnostic Aids
Programmable Speedometer/Odometer Module receives signal from ECU. The reasons why PSOM would not receive signal from ECU are:
- ECU has no ignition power (ABS light stays on after start up).
- VSS signal is not being generated, is bad or is not reaching ECU (ABS light may stay on, VSS code will set).
- Problem with wiring or connectors between ECU and PSOM (Likely to cause erratic PSOM function).
The ECU will send a signal to PSOM, even when disabled, except in first 2 cases previously described. This test only determines if ECU is NOT sending a signal. If testing verifies ECU is sending out a signal, go to INSTRUMENT PANELS article in the ACCESSORIES & EQUIPMENT section.
- Check ABS Light
Turn ignition on. Start vehicle. If ABS light comes on, go to next step. If ABS light does not come on, go to CHECKING ABS WARNING LIGHT SEQUENCE in PRETEST CHECKS. - Retrieve Codes
Retrieve and record any trouble codes. If only Code 16 is present, go to next step. If any other code appears, go to appropriate DTC TEST . If no code is present, go to step 1 . - Check Signal At PSOM Connector
Turn ignition off. Ensure vehicle is in 2WD. Disconnect PSOM connector. Raise and support vehicle with wheels clear of ground. Using care not to damage fragile terminals, measure frequency (Hz) at connector pins No. 4 and 5. while assistant spins rear wheels. If frequency increases with wheel speed, ECU is providing proper signal. Go to INSTRUMENT PANELS article in the ACCESSORIES & EQUIPMENT section. If signal is erratic, weak or missing, go to TEST K: REAR SPEED SENSOR (STATIC) .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.