Speed Signal, Checking
The following procedure requires a test drive. Observe all Safety Precautions.
Special tools and workshop equipment required
- Multimeter.
- Wiring diagram.
Test Requirements
- 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 .
-- 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:
| 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:
-- 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
After repair work, the following work steps must be performed in the following sequence:
- Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
- If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
- If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .