Symptom: a BMW 750iL (V12 cylinder M70 engine) sedan. Accelerated performance, the accelerator pedal stepped on the end. Found that the instrument panel on the engine speed meter pointer can only be raised to 2000r / min, the dashboard no fault light is lit, and the exhaust pipe to take white smoke, smell.

Fault diagnosis: repair this car, taking into account the engine failure light is not lit, so decided not to consider the reasons for electronic control, but from the basic oil, the circuit started. According to the phenomenon of "exhaust pipe" has a white smoke. Smelly "analysis, because the fuel mixture is too strong, incomplete combustion caused. Then check the oil pressure. Measuring sub-cylinder line and sub-fire and other resistance, are normal. Remove the spark plug to check and find all the spark plugs black, and there are four cylinder spark plugs signs of fire, so all the replacement of the original spark plug. Replacement after the test. The fault is removed after a few minutes. And then use the oscilloscope to check the ignition waveform, and check that the ignition sequence is 1 → 7 → 5 → 11 → 3 → 9 → 6 → 12 → 2 → 8 → 4 → 10. The results are correct, and then check the ignition advance angle of 10 °, is also normal.

Through the above test, after careful analysis, can be considered not oil, circuit failure. But where will the problem appear? With all sorts of questions, taking into account the BMW V12 Cylinder for the double inlet, there are two electronic throttle (EML.), Two throttle position control motors. Then try one of the (left) electronic throttle (EML) plug unplugged, and then do the accelerated test, the engine speed to rise, the failure immediately disappeared. Which is suspected to be EML. There is a fault, with a dedicated diagnostic instrument into the EML. System, read out a fault code "EML indicator failure", its specific meaning is the EML indicator line or light bulb problems, it may be EML module itself has a problem, after the transfer of the fault code analysis of the conclusions, First observe the dashboard, found that both the ignition switch or running, the dashboard EML fault indicator light is not bright. In order to quickly find a fault, here to introduce the BMW 750iL sedan EML control system.
This BMW V12 cylinder engine uses two sets of MOTRONIC (DME) engine control systems, in which the first group of DME control modules control 1-6 cylinders, the second set of DME control modules control 7-12 cylinders, and the electronic throttle control system (EML (EGS), anti-lock braking system (ABS), anti-skid control (ASC), and torque (DTC), in addition to the DME control module, the automatic transmission control module (EGS), the anti-lock braking system (ABS) Control (MSR) signal and calculate the DME control module and then the signal and its sensor signal to control the injection timing, fuel injection and ignition timing.

EML system in the accelerator pedal is equipped with a pedal position sensor, the main accelerator pedal opening signal feedback to the EML control module, and then EML control module and then output signal to drive the throttle body on the two throttle position control motor, use them To control the engine speed.

The BMW sedan has an EML control module connector for 55 feet. The 15th foot is connected to the instrument panel EML fault indicator. Then find the EML control module from the glove box and place the ignition switch in the "ON" position. Measured by the voltmeter 15 pin voltage OV. And then measuring the instrument panel A at 12V voltage, and 15 feet to the dashboard BC between the wire is also intact. So the cause of the EML system failure occurs inside the dashboard or the EML control module is damaged. In accordance with the principle of the first easy after the first, first open the dashboard check, the results of EML fault indicator line has been damaged (once repaired), so the use of fine copper wire to re-connect the line, start the car again, the fault is still, and The EML fault indicator is not lit. Obviously is the failure of the EML control module itself, for safety reasons. With the same BMW sedan exchange EML control module, and then the car test, the fault completely disappeared. The EML fault indicator lights up after turning on the ignition switch. With the extinguished.

Finally, with a dedicated diagnostic device to clear the fault code, the fault completely ruled out.

Fault Summary: In addition to the original EML system with self-diagnostic function, but also has a failure protection function, that is, when the EML system failure, it can send signals to the engine control module, the common control throttle position motor, keep the throttle a certain degree of opening Inhibit the engine speed, thus causing the engine speed does not fail.