GAC Toyota Camry: Malfunction Indicator Lamp (MIL) stays on
2026-04-03
Background
Vehicle Model: Camry 2.0
Mileage: 3,540 km
Fault Symptom
The engine malfunction indicator lamp stays illuminated. Multiple diagnostic tests were carried out previously; the warning light relit shortly after clearing the diagnostic trouble codes each time.
Repair Procedure
Upon vehicle acceptance, the engine malfunction indicator lamp was constantly on. The IT‑II diagnostic scanner retrieved DTC P0500: Vehicle Speed Sensor Malfunction.
After clearing the fault code and conducting a road test, the warning lamp lit up again after driving roughly more than ten kilometers, confirming an intermittent fault.
The fault lamp reoccurred soon after. We replaced the navigation unit as instructed by the repair manual and tested the vehicle, yet the problem persisted.
Freeze frame data was retrieved: engine speed 2300 r/min, coolant temperature 82°C, vehicle in D gear and driving state, while the scanner showed zero vehicle speed, though the speedometer on the instrument cluster displayed normal speed.
We monitored live data while driving and confirmed valid speed signals from all four wheels, ruling out a faulty wheel speed sensor.
Per the official repair manual, wheel speed sensors monitor wheel rotation and transmit signals to the skid control ECU, which then relays signals to the ECM via the combination meter. The ECM calculates vehicle speed based on the frequency of pulse signals.
Since the instrument cluster showed accurate speed readings, the skid control ECU was confirmed to output normal four‑pulse signals to the meter, eliminating the skid control ECU as the fault source.
Circuit resistance measurements between wiring harness connectors were carried out in accordance with the repair manual, and all readings were within standard range.
The skid control ECU sent valid signals to the combination meter, but no corresponding signals were transmitted from the meter to the ECM. We suspected a defective combination meter, replaced it and test‑drove the vehicle for dozens of kilometers with no engine warning light activation. The vehicle was then delivered to the customer with the fault deemed resolved.
However, the malfunction lamp lit up again after the customer drove approximately 1,000 km. The vehicle returned to the shop with the same DTC P0500 (Vehicle Speed Sensor Malfunction).
Following the previous troubleshooting logic, we replaced the ECM and road‑tested the car, but the fault remained unresolved.
As the vehicle had window tint film installed, we suspected water intrusion into Connector No.3 during the tinting process. Inspection of Connector No.3 revealed no signs of water. Further inspection of other wiring connectors found water residue and corroded pins inside the wiring connector on the right side of the main body ECU.
Reference to the wiring diagram identified terminals A41 (A) and A42 (B), the connector linking the combination meter and skid control ECU (see Figure 2).
After cleaning and repairing the corroded connector, a road test confirmed the fault was fully eliminated.
Water Ingress in the Connector Between Combination Meter and Skid Control ECU
Fault Summary
After cleaning the corroded terminals of the connector, a road test confirmed the fault was eliminated. Follow-up telephone calls with the customer reveal no abnormal issues have occurred since vehicle delivery.
This vehicle presented an unusual fault condition. Normally, DTC P0500 (Vehicle Speed Sensor Malfunction) can be simply cleared using the IT‑II diagnostic scanner. However, this fault stemmed from poor signal transmission caused by water intrusion and corrosion within the wiring connector.
Conclusion: For recurring fault codes that cannot be resolved after repeated clearing operations, technicians must inspect wiring connectors for corrosion or poor contact. Extra thorough inspection is required for vehicles that have undergone front windshield tint film installation.
