Symptom: a Nissan Bluebird (SR20 engine) sedan, the engine speed is difficult to more than 2400r / m, and start difficult. According to the owner to reflect the car before all normal, after this failure, has replaced several of the same type of air flow meter, but the fault remains the same. Troubleshooting: first check the air flow meter and its line. This engine is equipped with ternary catalyst models, so the air flow meter plug only three pins. When checking the air flow meter, it is found that the plug is dirty and only three pins are inserted in the flowmeter. So it is suspected that there may be a mistake when replacing the flow meter.
    Pull the three pins out and wrap the tape against other lines. Open the ignition switch, where 12V orange (OR) line is inserted in the b position of the flowmeter; the white line (W) is inserted in the c position and the other orange (OR) line is inserted in the d position. After finishing the wiring harness, re-test, the fault remains the same.
    Turn off the ignition switch, unplug the ECU harness connector, check the harness between the C port and the ECU port 17; check the harness continuity between the d port and the port of the ECU 16.
    Use Consult-Ⅱ or jumper to do self-diagnosis, the results of the air flow meter fault code. Use the method of pulling the battery negative, to eliminate the fault code, restart the self-diagnosis, the fault code still exists. Open the ignition switch, use Consult-Ⅱ in the "data monitoring" mode to read the air flow meter signal, or check the d port with a multimeter output signal, the voltage value of 5.11V, this value is significantly higher than the open ignition switch (shutdown) The value under the operating condition (ie less than 1.0V). So it can be concluded that the fault is caused by the air flow meter output signal is too high, but what is the reason for this?
    Although the owner said it had changed a few air flow meter tried, but after another test, the output voltage is still 5.11V. The vehicle even in the case of the car, the flow meter output signal value is still 5.11V, indicating that the fault is not due to other sensor input signal is not correct caused.
    From this we can roughly determine the fault caused by the ECU. With a wire in series with a few ohm resistance to help C ground, measured d port output is less than 1.0V. Then try the car, start very easy. Check the d port output is 1.3-1.7V (idle), so you can determine the failure caused by the ECU internal control.
    After replacing the ECU, everything is normal and troubleshooting.