Hi all- first post.
Disconnected battery for about a minute the other day, and when I reconnected it, the fuel gauge was pegged empty, and the temp gauge was pegged into the red. The car was cold.
Did the self test on the cluster, and all gauges swept up and down fine.
Tested the temp gauge by unplugging the sender unit under the intake manifold, and there was no change on the gauge. The manual said that if there was no change, there is a short to ground, or the gauge is busted. There are 3.5 volts supplying the sender, which seems right.
(ps this is the second instrument cluster to this car. The first one totally failed. This is a used one from a yard)
Sorry I can'toffer a better answer, but two things seem to stick out in this posting. First, did you ever find the cause of the original cluster failure? Secondly, without a schematic to look at, I wonder why the voltage going to the sender is not 12volts?
Please post whatever you find, kinda makes me wonder as well.
The first cluster was failing intermittently when I bought the car, but with different symptoms (totally cutting out, then coming back on when hitting the dash). I did try an overhaul of it, but gave up. From what I understand, the circuit board on these clusters are notorious for failing.
The schematic that I have shows that the supply and return for both sender units is supplied directly from the instrument cluster, so voltage is most likely not 12v (I also feel like I found someone else measuring that number online, since Bentley does not give a specific voltage spec). There are several grounds from the cluster, but I have no way of knowing if any are specific to those two units.
The only thing I can imagine, since 2 separate gauges fried in the space of 30 seconds, and both have supplies and ground from the cluster is that there is an internal short.
If there was a "short" I would think there would be obvious burn marks showing you exactly where the problem was, at least with the 1st one, if it was power related. If it was a signal that was shorted, I would think just one signal, say the water temp, wouldn't be working. I really don't know much about these units, so just understand I'm just trying to help work thru this problem you have. When you "hit the dash" and it worked, it tells me you probably have a bad/intermittant connection. Since the 2nd unit failed in 30 seconds, I'm wondering if the unit that it plugs into, a "computer module" if you will, is possibly the culprit? Maybe it has a bad/intermittant connector or it's just flakey? Is there such a unit?
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