Speed Signal, Checking

Diagnostic Procedures

Speed Signal, Checking

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• The Speedometer (G21) OK.

• The Motronic 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 ] Safety Precautions

- 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 wiring from the Motronic Engine Control Module (ECM) (J623) to the Instrument Cluster Control Module (J285) for an open circuit, Short to Battery (+), or to ground.

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

- If necessary, repair the faulty wiring connection.

- Assembly is performed in the reverse of the removal.

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.