Temp gauge not working

[calor]

So when I bought my E30, the temp gauge was somewhat working but jumping a bit. It would then idle at about 50% and stay there. Tapping on the cluster would sometimes make it move to be a little more accurate. Then after a few times driving it, it just stopped working altogether. Until I had disconnected the battery completely (for something else) and it would start working again but only for a very short period of time. Disconnecting the battery made it work like 3 times, but now it no longer ever does anything.

I read over the Wiki a bunch of times:
- https://www.e30zone.net/e30wiki/index.p ... Temp_Gauge
- https://www.e30zone.net/e30wiki/index.p ... ot_Working

What I've tried so far:
- Replaced the sensor altogether (brown plug)
- Replaced part of the cables going to the sensor
- Cleaned up a few ground wires to the chassis
- Tightened the screw on the back of the gauge cluster (both sides). They didn't seem to be lose at all
- Checked if the C109 plug was rusty, but the suggestion in the Wiki (cutting out the rusted part) has already been done by the previous owner it seems

I don't really understand what the Wiki tells me to do with the C101 plug

[BenHar]

I think there's a typo in the wiki.

"The Temp Gauge is driven by the Brown Plug, a heat resistor that screws into the engine head. Failure of the brown plug is rare, so it's best to first test at the C101 plug to determine whether the fault is in the engine bay or the instrument cluster. To test, first unplug the C101 and earth pin 4 (brown/purple wire). Now if you switch the ignition on, the gauge should go to full hot. If it does, repeat the test at the brown plug by removing the cable from the brown plug, and earthing the terminal with a piece of wire (for older cars with two-pin terminals, just bridge them together). If it now works, the issue is normally corrosion of the C191 plug. "

It should say " If it now DOES NOT WORK the issue is normally corrosion of the C191 plug."

Ben

[Brianmoooore]

Are the SI LEDs working properly in the instrument cluster, including being able to reset them?

[Kalimsnor]

Are the SI LEDs working properly in the instrument cluster, including being able to reset them?

No the red/green service lights never worked since I got the car
I've tried resetting it by connecting the diagnostic pins together, and nothing happened when turning the car to on (not starting the engine). Does this indicate the SI Batteries are done for and need to be replaced?

[Kalimsnor]

I've taken the entire instrument cluster apart to do some more digging. What I found:

- Seems like the previous owner already meddled with the SI board a lot
- The SI batteries are already replaced (seemingly). I can't really identify which type they are. Good thing is they don't seem to have leaked. High quality photos:
https://i.imgur.com/WLArmoE.jpg
https://i.imgur.com/1wcreD9.jpg
https://i.imgur.com/EH6E9O5.jpg
https://i.imgur.com/MREgSq8.jpg
https://i.imgur.com/QVuBH7p.jpg
https://i.imgur.com/dkzvYZ4.jpg
https://i.imgur.com/98YiMK9.jpg

- The bottom of the SI board is already.. well, look for yourself:
https://i.imgur.com/6L3VZKn.jpg
https://i.imgur.com/2e8tdE0.jpg
https://i.imgur.com/tVBD2ZS.jpg
https://i.imgur.com/Fmv2EOM.jpg

- There's a thing that seemignly leaked (or is it glue of some sort?)... I'm not sure what it is, I hope one of you guys can identify it:
https://i.imgur.com/JmPDRYX.jpg
https://i.imgur.com/oOGpqNN.jpg

[Brianmoooore]

To state the obvious, that board has been severely damaged by leaking batteries in the past, and someone (who appears to be have been reasonably competent at least) has attempted to repair it. Unfortunately, we don't know if they were totally successful, partially successful, or made no improvement whatsoever. Also, we don't know if there was any corrosive battery goo left under the lacquer anywhere which has eaten more track away.
The SI board doesn't contain the electronics for the speedo/odometer and the brake pad warning light, and doesn't have much do do with the fuel gauge, but does contain the electronics for everything else in the cluster.
Given that the temp. gauge has not responded to the normal methods of repairing it, and the state of that board, I'd recommend at least finding a replacement board or complete cluster to try.
Have you measured the voltage across each battery?

[Kalimsnor]

To state the obvious, that board has been severely damaged by leaking batteries in the past, and someone (who appears to be have been reasonably competent at least) has attempted to repair it. Unfortunately, we don't know if they were totally successful, partially successful, or made no improvement whatsoever. Also, we don't know if there was any corrosive battery goo left under the lacquer anywhere which has eaten more track away.
The SI board doesn't contain the electronics for the speedo/odometer and the brake pad warning light, and doesn't have much do do with the fuel gauge, but does contain the electronics for everything else in the cluster.
Given that the temp. gauge has not responded to the normal methods of repairing it, and the state of that board, I'd recommend at least finding a replacement board or complete cluster to try.
Have you measured the voltage across each battery?

I agree it does look like that. Right now the car is away for a week for a big service, fixing rubbers I can't reach myself without a lift. Next up when it's back is measuring up the voltage of the batteries. and I've also placed a request at an E30 specialist nearby to look out for new batteries and hopefully a new cluster altogether. I'll keep this post updated!

Do you happen to know what this part is?
https://i.imgur.com/JmPDRYX.jpg
https://i.imgur.com/oOGpqNN.jpg

[Brianmoooore]

Sorry, forgot to add that to my last post. Not certain what it is, but I'd guess it's the crystal that determines the clock frequency for the processor. It hasn't leaked - that's hot melt glue.
The batteries themselves look near new, so I doubt if there's anything wrong with them, but I wondered about the voltage across them to see if they'd lost their charging voltage, which comes from the same basic source as the supply for the temp. gauge.