Model: CRH engine, 0BH transmission.
Driving Mileage: 24,000 miles.
Issue: The tire pressure light is on when the vehicle is driving.
Diagnosis: the diagnostic instrument detects the vehicle fault code, ABS controller fault code: 01314 engine control unit, please read the fault code; engine control unit fault code: 00257 air quality sensor 1 signal is unreliable.
The circuit diagram of the air quality sensor G70 is shown in Figure 1.
SC15 powers the fuse for the air quality sensor, as shown in Figure 2.
Analysis of the cause of the failure:
- Air quality sensor failure
- Line fault
- Engine control unit failure
- Leak in the intake system
- Other failures
Check the line from the air quality sensor to the engine control unit: the fuse SC15 supplies power to the air quality sensor T5u/3, which is normal after inspection. The lines from the engine control unit T94/23 to the air quality sensor T5u/1 and the engine control unit T94/65 to the air quality sensor T5u/2 are checked normally, there is no open circuit, no short circuit to the positive pole, short circuit to the negative pole, and mutually short circuits.
After confirming that there is no fault in the line, the maintenance technician replaced the air quality sensor G70 of the normal vehicle. The test failure did not reappear, and the vehicle was handed over to the customer. After the customer used it for a week, the fault came out again, and the fault code still pointed to the air quality sensor G70.
Check the line of the vehicle again, and still no fault was found. The service technician suspected that the vehicle engine control unit J623 was faulty, and the test drive failed after replacing the normal vehicle engine control unit. This time the maintenance technician found the author, hoping to give maintenance instructions.
Since the related parts have been replaced and the circuit inspection has no fault, considering the possibility of system leakage, the reason has always been the aspect that the maintenance technician has not checked. View the air quality sensor data stream.
The normal vehicle is 3.0g/s. The value of this vehicle is slightly too large. Carefully check the air intake system of the vehicle and found that the turbocharger cooler is not installed properly, causing the air intake system to leak. There are a lot of oil stains. , As shown in Figure 3.
Troubleshooting: Install and tighten the intake pipe. Test run and the fault is eliminated!
Summary: The case is a very simple fault. Since the fault is sporadic, the maintenance technician cannot catch the fault phenomenon, and blindly changing parts cannot quickly and accurately find the fault point.