SOLVED! Just another cluster issue - RPM & MPG dead

[Torsen]

Well, the revcounter and MPG meter stopped working some time ago. I took the cluster out and checked batteries, reading 3 volts. I checked and resolder bad looking joints. Refitted and still not working. Then, I resetted service leds and now the INSPECTION light is flashing. Oh, it's an E30 318is. What sould I check next?

Help much appreciatted.

Thank you.

[DesktopDave]

Might be a bad rev counter (tachometer).  The economy meter has to get the RPM & speedometer inputs to calculate, otherwise it won't work correctly.

Do the same reset you did for the oil lights, only longer.  That will reset the inspection light.

[Torsen]

I've bought a secondhand (reputedly working) cluster and the failure is still there. Now:

-I've kept my "old" coding plug. Could the problem lie there?

-How can I test the connectors? As long as fuel cons is working ok in OBC II, I understand fuel rate signal is fine.

Ideas?

Thank you.

[DesktopDave]

Coding plug is just a bit of bytecode on a PROM to change the scale that the gauges use, I haven't seen them fail very often.  The later eprom versions (e34, e36 e38) are less reliable.

I'd figure that the common failure is the signal coming into the cluster.  Seems like you've eliminated the gauge and the cluster SI board as causes.

You'd need an oscilloscope to test the DME signal properly, but I'll bet it'd be pretty easy to see a fixed value off that wire.  I was searching for that in the BMW service manual, but the diagram wasn't making sense to me.

[Torsen]

Well, I'll try to check signals according this. I hope to find something

[Torsen]

SOLVED! I tried a mate's coding plug and everything works.

Thank you for your help.

[DesktopDave]

That's good to hear.  Those plugs are getting old, I'll add that to my "things to check" list next time someone's gauges go dead like that.