Speed Signal, Checking

Speed Signal, Checking

The following procedure requires a test drive. Observe all safety precautions.

Special tools, testers and auxiliary items required
- Multimeter.
- Wiring diagram.

Test requirements
- The Speedometer G21 OK.
- The Engine Control Module (ECM) J623 fuses OK.
- Battery voltage at least 12.5 volts.
- All electrical consumers such as, lights and rear window defroster, switched off.
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.

Function test
- Connect the scan tool.
- Perform a road test with a vehicle speed greater than 5 Km/h.
- Using the scan tool, Check the vehicle speed:

Diagnostic text Specified value
Vehicle Speed Approx. Vehicle Speed

- Compare the vehicle speed on the scan tool to the Speedometer G21.

Specified value: a difference of no greater than 10%.

If the specified value was not obtained or no speed was displayed:
- Check the wiring from the Engine Control Module (ECM) J623 to the Instrument Cluster Control Module J285 for an open circuit, Short to Battery (+), or to Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.

Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase the DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If the DTC memory was erased, generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

- End of diagnosis.