540 Engine check light codes

[jraven2]

I have a 99 540i and the engine check light is on. Unfortunately the closest BMW delaer is 2 hours away, but I do have a good and honest independent mechanic who was BMW trained. Unfortunately he does not have full access to all their diagnostic equipment and manuals.

At the present time my car is running fine, but the engine check light keeps coming back after the faults are cleared, and I need the faults gone in order to get an emissions test done prior to license renewal next month.

If anyone can help with ideas about the cause of the faults it would be greatly appreciated.

The faults are:
1) Fuel trim at part load below threshold, multiplicative converter bank 1;
2) Fuel trim at part load below threshold, multiplicative converter bank 2;
3)Electronic thermostat control final stage.

Thanks in advance for any suggestions.

[Dirty_Tool]

the 1st 2 are basically fuel trim faults meaning fuel mixture is off. what u posted is very general. it doesnt say if its off on the lean side or the rich side. Common causes could be a bad MAF or vacuum leaks from intake gaskets or any other place. Thats about the best I can do with the general description you gave. Have your mechanic check the short and long term fuel trim values (any generic obd2 scanner should do that) and if he knows what he is doing he should be able to tell if its rich or lean and then go from there.

#3 is basically just a bad MAP thermostat (electric coolant thermostat) I would just replace it.

Good luck