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I have a 1999 Oldsmobile Cutlass. My problem is that recently we experience both the temperature guage and fuel guage stopped working. Up until this problem, we had occasionally experienced the fuel guage dropping to zero and returning on it own with long periods of fully functioning. I traced the fuse to position 37 in the under hood fuse box. It is listed as ac/bfc which to my understanding has to do with either the AC or cooling fans but seems to be used by other systems as well. Our AC is fine and functioning and there is no problem with overheating. Upon replacing the 10am fuse and turning the key, both guages return to function and read where expected for about 5-10 sec and then they blow the fuse. I have tested this several time with similar result. In researching this problem on the internet I came on advice that this is a typical problem for a number of GM models over the years and with the description of my situation to a T it pointed to a defective Dash Voltage Regulator or Voltage Limiter that perhaps can be found behind the instrument cluster. Upon check with several parts supplier and the local Chevrolet / Cadilac dealer parts department, there seems to be no such part nor had the parts manager ever hear of a similar problem.. My Haynes manual is of no help either. So does any one have more advice or knowledge to this problem? Help is greatly appreciated..... Mike

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the fuse that you are talking about (ac/bfc) is for the ac clutch relay and the body control module, it is the key on power for them (after the ignition switch is turned on)

you could try pulling the ac clutch relay out and see if the fuse stills blows or not. if it still blows you are going to have to look into your under hood fuse box. You may have a short inside the box itself. You may have to separate the circuits to see if the problem is in the wire that goes to the BCM. it is the pink wire that goes to the B9 pin on the BCM.

what you could do is take out the ac relay and unplug the BCM. Take out the fuse. turn on the key so the dash comes on. Use a volt meter and check the two prongs where the fuse came out from. There should be on side that has your keyed power. (you can verify by having someone turn the key on and off and see if the power go on and off as the key is moved) the other prong should show nothing. No power and no ground. If it does show a ground then you need to look for the short. If it shows that there is no ground the you may need to separate the two circuits and test them separately. You may have to to verify the ac clutch diode is normal. If you have an inductive amp meter you could check the amperage to the compressor coil when the ac turns on to see it it is using too much amps.

if the gauges work fine and the fuse doesn't blow with the ac relay out, plug the relay back in and unplug the compressor coil. see it it blows the fuse now or not. If it doesn't blow the fuse then you probably don't have a short to ground in the circuit but probably have a short in the coil.

oldsmobile-ac-bcm-schematics.jpg [ 43.55 KiB | Viewed 1149 times ]
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