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 requirement

• The function and display of the Speedometer OK.

• The Engine Control Module (ECM) (J623) fuses OK.

• Battery voltage at least 12.5 V.

• 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.

Test procedure

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

- Connect the scan tool.

- Perform a road test with a vehicle speed greater than 5 Km/h.

- Using the scan tool, have an assistant observe the reading on the display:





- 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:

- End the diagnosis and switch ignition off.

If no speed is displayed:

The speed signal is transferred from the Engine Control Module (ECM) (J623) to the instrument cluster through the wire connection or through the CAN-Bus, depending on version.

- Check the wiring connections.

- Check the terminal resistance for CAN-Bus Refer to => [ Can-Bus Terminal Resistance, Checking ] CAN-Bus Terminal Resistance, Checking

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

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

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

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