Please Explain Code 1231- Battery Voltage/DME Main Relay

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ryan - 04 Apr 2004 00:13 GMT

I have a 1990 325is. The check engine light sporadically flashes at
me, it seems to not like going over bumpy roads. The code that the
odb gave me was 1231, the Battery Voltage/DME Main Relay. Can some
one please explain this to me.
I know that my interior and exterior lights pulsate, which suggests I
should get a new voltage regulator. I'm working on doing that, it
happens to be a real pain when the regulator is under the alternator
cap. Would replacing the voltage regulator most likely solve the
check engine problem? I have read about all types of relays but have
not been able to find any information about a "DME main relay". I
need to know where this thing is, if I can test it, and how to replace
it. Also, to check battery voltage I can just put a volt meter on the
battery while the car is running? I know next to nothing about
electricity and don't want to break anything or give myself a jolt.
Thanks for any help you can give.

Ryan

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Dave Plowman - 04 Apr 2004 21:09 GMT

> I know that my interior and exterior lights pulsate, which suggests I
> should get a new voltage regulator. I'm working on doing that, it
> happens to be a real pain when the regulator is under the alternator
> cap.

The most likely cause is worn/sticking brushes - if the mileage is fairly
high. Best get it seen to before the alternator packs up altogether.

Many things on a BMW are rather sensitive to a poor volts supply - whether
caused by the battery or alternator. Fix this first before spending out on
anything else.

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Dave Plowman dave.sound@argonet.co.uk London SW 12
RIP Acorn

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ryan - 04 Apr 2004 23:29 GMT

> I have a 1990 325is. The check engine light sporadically flashes at
> me, it seems to not like going over bumpy roads. The code that the
[quoted text clipped - 4 lines]
> happens to be a real pain when the regulator is under the alternator
> cap.

I have talked with a mechanic and he said that often replacing the
volatage regulator on an internally regulated alternator does help
correct the voltage fluctuations. Has anybody had any success with
installing a new voltage regulator, or is replacing the whole
alternator in the future seem like a better option?

Would replacing the voltage regulator most likely solve the

> check engine problem? I have read about all types of relays but have
> not been able to find any information about a "DME main relay". I
> need to know where this thing is, if I can test it, and how to replace
> it.

I think I have found the main relay. its in the auxilliary relay
panel, its white, and has two fairly large (4mm) wires running to in
in addition to smaller wires.

Also, to check battery voltage I can just put a volt meter on the

> battery while the car is running? I know next to nothing about
> electricity and don't want to break anything or give myself a jolt.
> Thanks for any help you can give.
>
> Ryan

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