Speed Signal, Checking
The following procedure requires a test drive. Observe all safety precautions. Refer to SAFETY PRECAUTIONS .
Special tools and workshop equipment 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
-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK
Start diagnosis
-- 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 in the ECM:
| 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:
-- Some models have a transmission speed sensor input to the TCM while other models get the signal on the CAN bus from the ABS module. Check the ABS module for wheel speed sensor fault codes, and if present repair the fault. Refer to Wiring Diagrams to determine if vehicle is equipped with a VSS or is ABS driven.
Final procedures
After the 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 .