Step 1: Connect the diagnostic instrument to the diagnostic interface, enter the system to read the fault code, and view the fault code.
See if the failure of the airflow meter leads to the speed limit of the vehicle, the electronic control diagnosis is really convenient and quick, so quickly change the airflow meter.
Step 2: Replaced with a new airflow meter, quickly try a car, but how does it feel that the speed is still limited? I drove it back and checked it. It was strange, the fault code was still there, and I was bluffed by the hardware fault. After thinking about it carefully, I chose to measure the broken skin voltage of the airflow meter to further determine the problem. It turned out that the voltage data was 12.56V, 8.5V, 7.78V, and 7.74V, which was obviously wrong. Compared with 12V, 3V, 2V and There is too much difference in the 0V data. Since the previous air flow meter itself should be no problem, it is a fault in the wiring harness.
Step 3: Check the continuity of the sensor by flying the wire directly to ensure that the signal voltage is correct and replace part of the wiring harness. But when we plug in the airflow meter to measure the broken skin voltage, eh? The signal voltage is still abnormal. What is the situation? Since the airflow meter has been replaced and the wiring harness has been replaced, what could be the problem? Is the computer version broken? In this case, changing a computer board can cost a lot of money.
To be on the safe side, you still have to be responsible to the customer. Check again to see if something is missing and unplug the airflow meter. At this time, I accidentally glanced at the airflow meter harness plug and felt something was wrong. After inspection, I found that there was something in the plug. Two pins are short-circuited! No wonder even if the wiring harness is replaced, there is no way to return to normal and clear the fault code. It turns out that the little guy is hiding here.
After the plug is replaced, the measured voltage returns to normal, connect the diagnostic instrument to clear the fault code to confirm that the system is normal, and the test speed limit has been completely resolved, and the fault is thus eliminated.
For the above cases, many masters often encounter problems with the wiring harness or the airflow meter itself, because the three major failure modes we often say are "sensor, wiring harness and computer board". However, as in the above inspection process, what we call "wiring harness" refers to not only the wires and wires but also the part of the plug that connects the airflow meter and the wires. This part of the damage also needs our attention.