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Malfunction Indicator Light (MIL) On

Malfunction Indicator Light (MIL) On Brand: BMW Models: M3 E90, E92, E93

Symptoms
The customer’s complaint is that the malfunction indicator light (MIL, Check Engine light or Check Engine Soon light) is illuminated. Also the engine runs rough or will not accelerate.

Fault codes 

Various fault codes may be stored in the engine control module (ECM) indicating malfunctions in the throttle body.
Plug in your AssistPlus and run a Quick Test to see if you get any of these fault codes:
2B1F – DME Throttle valve sensor, bank 1
2B20 – DME Throttle valve sensor, bank 2
2B21 – DME Throttle valve actuator pre-drive check, bank 1
2B22 – DME Throttle valve actuator pre-drive check, bank 2
2B23 – DME Idle actuator governor monitoring, bank 1
2B25 – DME Throttle valve monitoring, bank 1
2B26 – DME Throttle valve monitoring, bank 2
2B27 – DME Throttle valves, test of return springs, bank 1
2B28 – DME Throttle valves, test of return springs, bank 2
If you have one or more of these fault codes stored in the ECM, test the throttle actuators.

Causes

Worn plastic gear in throttle housing
  • Dry, loose or burnt soldered joints in throttle housing circuit board

Repairs

  • Road test the vehicle to confirm the customer's complaint.
  • Carry out a Quick Test and check the fault codes stored in the ECM.
  • If the fault is stored for one bank only [example: DME Throttle valve actuator pre-drive check, bank 2 (2B22)], start by swapping the throttle bodies between bank 1 and bank 2.
    • If the fault travels to the other bank, the cause is the throttle motor itself. You can disassemble the throttle housing and check for wear in the plastic gears. You can also check for loose, dry or burnt solder joints on the transistors.
    • If, during the throttle swap, the fault code does not travel and change sides, check and repair the wiring between the ECM and the faulty throttle.
    • If the fault is stored on both banks, check the wiring to both throttle valve actuators from the ECM. If the wiring checks out OK, repair or replace both throttle valve actuators. 
    • The soldered joints in the circuit board can be cleaned and resoldered. Plastic gears can be replaced.                                       
Note that no throttle housing repair parts are available from BMW. BMW only provides the complete replacement throttle housing. 
  • After repairs or replacement, run the throttle valve actuator test to allow the ECM to run the motors from MIN to MAX positions and learn the end stops. To do this on your AssistPlus go to:
DME >> SERVICE FUNCTIONS >> THROTTLE VALVE ACTUATOR GROUP TEST >> SYSTEM TEST THROTTLE VALVE ACTUATO

The car is fixed when the engine runs correctly and there are no throttle related faults stored.

Master tech tip
If the wiring checks and throttle housing checks prove to be OK, this indicates a faulty ECM, but that is rarely the problem.