Vehicle

BMW 520 E39 1996

Symptom:

R/h/f  high beam (main beam) light always on

The client had removed the wiring to the R/H/F high beam light as it would drain the power from the vehicles battery and cause it not to start.
After initial consultation we decided to check the system power fuses etc, and check what is at the high beam light connection on the left hand side the was only an earth present, on the right hand side the earth and a power source was present, which explains why the high beam light is on, the circuit is a power switching circuit.

We then consulted a workshop manual to find out more on the head lights, The head lights are controlled by an ECU known as the LCM (light control module), the light modules location is R/H/F kick panel (drivers side in a right hand drive vehicle).

Then it was time to connect the scan tool to the vehicle, the vehicle had an LCM module connected to the vehicle so we decided to connect to that module and check for fault codes, on initial check of the faults codes we had 6 fault codes, the fault codes did not relate to our problem so we decided to clear the fault codes and restart the procedure, once testing the system again we then came up with a fault code 14

code 14 – POWER-MOS STAUS SIGNAL 1 CONTINUOUS ACTIVE.

By no means could any one understand this, we went back to consult the workshop manual and found that code 14 is an internal ECU fault, which made sense knowing that the power circuit did not switch off as the transistor, and that the transister was not dropping the voltage, even with ignition off.

Once the New LCM has been fitted the LCM must be programmed to the vehicle, The LCM stores the speedo reading in 3 places the DME, Instrument cluster and the LCM, if one of the three does not correspond a red dot on the instrument cluster will be displayed.

Extras

Repair_of_LCM_on_an_e39
written by Mats Isaksson Poweruser on Autopower.se

LCM – Fault Code table