I have a 1984 BMW 533i with the early OBC. Spent many hours trying to diagnose why the OBC display is dead. I've checked voltage on all the appropriate wires, the bulb is new and good, the fuse in the OBC itself is new and good, all fuses under the hood are good and connected tightly. All power is getting to the OBC itself. However, coming out of the OBC going to the display there is supposed to be a +5v on pin 12 and +8v on pin 25. I'm getting the +5v on pin 12 but only +.725v on pin 25 (this is on the yellow connector). I've poured over the wiring diagrams and the Bentley manual. Everything seems to test good going into the OBC. The ground is attached to the OBC case as it should be. And that ground is good.
A little background. The OBC display wasn't working when I bought the car. I replaced the correct fuse in the OBC itself, then it worked. Car say for 1-2 months while I was waiting on AC parts. During this time, the battery was either disconnected or hooked to a battery tender.
How likely is it that the OBC (silver box by driver's foot) is bad?
Last edited by klavender1; 10-10-2019 at 03:44 PM.
Very good chance the OBC "brain" is bad- Shoot me a PM, I have known working units
I'm not sure how on the mobile version of this site. Can you pm me?
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