Speed Signal, Checking

Speed Signal, Checking

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 connections between engine/transmission/chassis OK.

• Ignition switched Off.

Test procedure

- Observe safety precautions. Refer to => [ Safety Precautions ] Generic Scan Tool

- Observe Clean Working Conditions. Refer to => [ Clean Working Conditions ] Clean Working Conditions

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check.

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:






- 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 ABS module with a scan tool for a proper wheel speed signal. The ABS module will send this information over the CAN bus to the Instrument Cluster and ECM. If a wheel speed sensor code is set in the ABS module, refer to the repair information for ABS diagnostics. Some models will receive the signal from the transmission speed sensor. Refer to wiring diagrams for sensor location and wiring.

- Check the wiring connection for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

Final procedures

After repair work, the following work steps must be performed in the mentioned sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.