Failure phenomenon: a 1996 annual production BMW E38750iL sedan, equipped with M70 V12 engine. According to the user to reflect the car suddenly did not accelerate the speed, that is, step on the accelerator pedal after the engine did not respond.
    Check the analysis: After receiving the car, the maintenance staff found that the fault is indeed as described in the user, step on the accelerator pedal engine no response. Use the fault diagnosis instrument GT1 into the electronic throttle EML system control unit to read the fault code, a total of four fault codes, namely: 50/51 (acceleration pedal position sensor basic adjustment settings), 26 (acceleration pedal position sensor 1 signal failure ) And 54 (accelerator pedal position sensor failure). After the fault code is recorded and cleared, the fault codes will reappear, indicating that the faults are current faults.
    Before proceeding with troubleshooting, it is necessary to briefly understand the electronic throttle system of the M70 engine. M70 V12 engine with dual inlet, with two electronic throttle, the engine uses two DME engine control unit, a DME control unit control 1 to 6 cylinder, another DME control unit control 7 to 12 cylinder. The accelerator pedal position sensor feeds the stroke signal of the accelerator pedal to the EML control unit and then drives the throttle motor by the EML control unit output signal to control the engine speed.
    Because the stored fault code is prompted to accelerate the pedal position sensor failure, so the maintenance staff decided to check the relevant line. The vehicle uses three accelerator pedal position sensors to ensure that the vehicle is still able to receive the driver's demand signal from other sensors when a sensor fails to ensure traffic safety. The three measurement result signals are transmitted to the EML control unit via three shielded feedback lines and processed in the three analysis circuits of the control unit. The EML control unit harness connector is 55 feet, according to the EML system control circuit diagram, with a multimeter to measure the accelerator pedal position sensor to the EML control unit line, which has two lines of resistance is low, a PWG1_SIG is 3Ω, The other PWG3_SIG is 5Ω. Correspondingly, two jumper wires from the EML control unit are connected to the accelerator pedal position sensor and the fault codes 26 and 54 are found to be cleared, leaving the fault codes 50 and 51, thereby determining that the fault is on the line. Remove the jumper, check the accelerator pedal position sensor to the EML control unit between the lines, found in the line with multiple tape wound. One by one after the opening of the tape and found that the internal wiring harness has been rusted, it should be the previous maintenance personnel did not follow the provisions of the line connection, but simply hand thread will be twisted together, after a period of time there will be corrosion, resulting in contact Bad and signal distortion. The correct way to repair this line is to solder the connection point and shield it after welding.
    After properly handling the line, use the fault diagnosis device GT1 to detect and clear the fault code, then a matching prompt appears. Using GT1 to accelerate the pedal position sensor matching, but the matching process has emerged a new problem. There is no problem when the GT1 is prompted to depress the accelerator pedal to perform the first step, and the second step operation can not be performed again, and the system can not recognize the correct signal of the accelerator pedal position sensor 2. Fig. The trouble code inquiry is performed again, and the trouble code of the accelerator pedal position sensor 2 is newly displayed. Clear the fault code again after the match, but also appeared the same fault code, because the relevant lines have been checked, thus judging the accelerator pedal position sensor 2 has been damaged.
    The car uses a Hall-type accelerator pedal position sensor manufactured by Siemens, which has the advantage of no contact without wear and long service life. The pedal position sensor is used to record the driver's requirements by accelerating one of the pedal position sensor PWG The coil generates a measurement signal proportional to the position of the accelerator pedal. The EML control unit has a self-test function, a calibration function, and a basic adjustment of the PWG sensor. The idle and downshift positions of the PWG sensor are determined in the adaptive mode of the basic adjustment. Therefore, when replacing the EML control unit or accelerating the pedal position sensor, the PWG sensor should be re-calibrated and the correct PWG sensor should be adjusted. • Troubleshooting: Replace the accelerator pedal position sensor, follow the steps shown in GT1, Commissioning troubleshooting.