fault code 1-2-3-1
 

Hey guys, I'm new to the forum here and I'm hoping someone can help me out with an issue I'm having in my 1994 318is. As the title says, the car is throwing the fault code 1-2-3-1. I know it's the fault code for the DME main relay / battery voltage. I've been trying to track down the source of the problem with no luck.

The check engine light will randomly flash on and off every once in a while for a brief period. The light will come on for about one second then disappear. Sometimes it will go problem free for days and other times it flashes many times within a minute. However the light never stays on all the time. Every time the light comes on, there is excessive voltage running through the car, because the headlights get brighter (almost like high beams), the A/C and heating blower fan starts revving faster, and even the windshield wipers will work faster. The voltage only seems to go up for these short one second periods - triggering the check engine light. It sometimes causes the dash lights to go out and most of the time causes the aftermarket stereo to cut out, due to this surge in voltage.

So far I've had the alternator checked out to be good and the battery has also been replaced. I've pulled the DME out of the car - the DME compartment is dry, but the case for the DME as little spots of corrosion on the aluminum as if it's been damp in the past. All the connectors on the DME and wiring harness plug are also clean and corrosion free.

Sorry for the long winded explanation, but does anyone have any suggestions as to what might be causing these voltage surges? Is it possible for the DME to cause these voltage spikes? Any suggestions would be greatly appreciated. I can't think of anything within the car that would cause the electrical system to produce excessive voltage.

Replace the voltage regulator or just replace the entire alternator.

The voltage regulator was my only other thought. I can't think of anything else that might cause excessive voltage.

I cant either. I'm pretty sure it is replaceable. On some models there is even an aftermarket part. I think the aftermarket part was originally designed for a Volvo alternator.