Latest company case about GAC Toyota Camry Engine ECU Malfunction

GAC Toyota Camry Engine ECU Malfunction

2026-04-01

Background

Vehicle Model: GAC Toyota Camry

Fault Symptoms

This Camry was involved in a road accident outside the local area two months ago with severe damage to the front end. Due to various factors, the vehicle was not repaired at an official Toyota 4S dealership; instead, the owner took it to a nearby general repair shop. When picking up the car, the owner noticed abnormal driving performance: obvious shaking occurred at idle speed as well as during vehicle launch and stopping. The repair shop claimed the vibration would disappear after some driving since the engine had just undergone a major overhaul.
The vehicle has been driven for more than one month, yet the shaking issue shows no improvement. Recently, a new abnormal rattling noise appears when turning the steering wheel left or right. The car was sent to a friend’s repair shop for four days of troubleshooting without any fault being located. The owner now entrusts our dealership to diagnose and fix all defects.

Fault Analysis

Technicians verified all symptoms on-site, consistent with the customer’s description: severe engine vibration, and a distinct clicking sound from the chassis when turning the steering wheel left or right at low speed.
After opening the engine hood, technicians found many engine components improperly installed. The engine had been fully disassembled previously, and most replacement parts fitted were non-OEM spare parts. The technician communicated with the customer about conducting a full vehicle inspection, which the customer agreed to, leaving the vehicle at our workshop for further diagnosis.
First, the technician reinstalled all misassembled engine parts and retightened all chassis bolts. It was found that the through bolts on the left and right lower control arms were not torqued properly. After fully tightening these bolts, the abnormal steering noise was completely eliminated.
Regarding the persistent engine shaking reported by the customer, the technician sorted out potential root causes as below:
  1. Resonance between vehicle body and engine
  2. Defective ignition coils
  3. Faulty spark plugs
  4. Malfunctioning fuel injectors or their wiring harnesses
  5. Intake system failure
  6. Exhaust system failure
  7. Internal mechanical faults of the engine


Troubleshooting & Repair Solution

Standard preliminary inspections were carried out:
  1. All three engine mounting cushions were inspected and confirmed intact.
  2. Cylinder balance test was performed on ignition coils, and spark plugs were removed for inspection; no abnormalities found.
  3. Cylinder balance test for fuel injectors returned normal results.
No Diagnostic Trouble Codes (DTCs) were retrieved via the IT-2 diagnostic scanner. Live data streams were then captured, including signals from the oxygen sensor, mass air flow (MAF) sensor, injection pulse width and engine speed. After comparing data readings with an identical fault-free Camry, the faulty vehicle presented abnormally low oxygen sensor and MAF values, with engine speed fluctuating between 735 r/min and 983 r/min.
Taking oxygen sensor data as the core diagnostic reference and adopting reverse deduction: the oxygen sensor voltage only fluctuated within 0.01V to 0.03V. Combined with the working principle and function of oxygen sensors, it was determined that the air-fuel mixture was persistently too lean (excess air, insufficient fuel), which indicated air leakage inside the intake system.
A targeted inspection of intake pipes and vacuum hoses downstream of the MAF sensor found the rubber hose connecting the PCV valve to the intake manifold cracked and leaking air from aging under long-term high temperature.
The technician temporarily blocked the cracked hose, which greatly alleviated engine vibration and stabilized engine speed at 739 r/min. However, subtle abnormal shaking still remained compared with other same-model vehicles. Further inspection revealed the canister purge solenoid valve had been manually modified to stay open permanently and failed completely.
After replacing the cracked PCV valve hose and defective canister purge solenoid valve, plus throttle body cleaning, all vehicle malfunctions were eliminated and performance fully restored.


Summary

Improper maintenance work conducted at an unauthorized non-Toyota repair shop led to multiple man-made faults and raised difficulties for secondary repair. Through careful logical analysis, professional technical knowledge, live data comparison with a reference vehicle, the technician successfully identified and resolved all faults, greatly boosting customer satisfaction.