AH HA! It was the coding plug...

[Zackb911]

My cluster works! After hours of reading the possible causes for why my cluster wasn't working and suspecting something more than capacitors I finally fixed it! I suspected my old cluster's LCD box to be shot and possibly the capactiors, so I replaced the entire thing with a tested and working one. But still my fuel gauge, temp gauge, OBC, and LCD display didnt opperate right... Well I had read on Bruno's site that the coding plug can also get corrupted so I found a used one on eBay, popped it in, and all is well!!

Well except that I blew the headgasket last week but thats another story...

Anyway the coding plug I got was really for troubleshooting and is high mileage ~197K, anyone know where I could get a new one, lower mileage ~120K, or get a preprogrammed one? The car is a pre 2/89 so it is in the wiring harness

[Barry]

Z,What the heck is a coding plug ???
You have a link?
Thanks.

[Paul in NZ]

its a interfae between the harness and the instrument cluster

[Ross]

Has your cluter now assumed the identity of the donor car?
Can these plugs be reprogrammed with your data?

[Zackb911]

Has your cluter now assumed the identity of the donor car?
Can these plugs be reprogrammed with your data?

Yes and that is where is gets tricky... The coding plug on pre 2/89 built cars is in the loom and on post 2/89 in the cluster itself. It is non-volitile memory so should always retain mileage etc. However they can be corrupted as mine became. They contain the mileage but also interfce with the OBC as well. So on my car the OBC, mileage display, message lcd display, fuel guage, and temp gauge were non functional. The replacement plug popped right into the harness and fixed all the problems but now displays the mileage of the donor car which is about 65K miles too much

The older plugs are supposedly harder to read and are no longer available by BMW, the newer ones are supposedly easier to read an write with an EPROM reader. I just need to find an older plug with mileage close to mine. Also you can get the newer style plugs on eBay and the dealer, they will reset your mileage to zero if they are new, however the stock plug has your VIN, etc so someone savvy will know if its been replaced.

[Ross]

At least you can save the old coding plug to document what mileage was before change.

[Zackb911]

Well I have the original coding plug which is corrupted and probably useless, so I only have an estimate of the mileage from the carfax.. It is kind of a mute point anyway because the car had gone in for inspection before with the mileage not displayed and therefor has been branded TMU or True mileage unknown oh well

[Zackb911]

I've sent an email to Programa Inc who specializes in the clusters and various electronics to see if they sell or can reprogram these. I will keep you guys posted!

[NielsGalan]

I had a similar problem a few years ago. Erratic or non functioning rpm gauge, econometer etc.

The problem turned out to be in the coding plug. Now, I don't know what the coding plug looks like in a 535, but mine doesn't contain much more than a microchip and a couple thingamajigs on a circuit board. My father, who is an electrician, determined that the solderings were bad between the chip and board. Not visible to the naked eye, but the solderings were cold, causing the thing to fail on and off (mostly off :-)

After re-soldering the legs of the chip back onto the circuit board everything was fine. And the car lived happily ever after.