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Cadillac Repair/1991 cadillac sedan devile


I have a 1991 cadillac sedan devile and in the middle of summer my a/c, heater, defroster, and digital gas guage and digital temperature guage dont work. I need the car for the winter... what do i do?


We are looking at 2 unrelated circuits. The fan blower for the W/o is a common problem. It's been so long since I worked on these, I can only describe the two types of heater blower circuits. You are going to have to look at your vehicle and see which one applies.

CADILLAC USED ONE OF TWO stakes across all their lines for the heater A/C blower control.

One sale involved a resistor block that was non-serviceable located under the hood on the passenger side at the A/C plenum. This design is easy to identify. The module had a number of wires in it, with only one going to the blower motor at the firewall. If this type is in your vehicle, you have problems if the module is bad, because they are almost impossible to find need and are over $400. Chances of finding a good one are slim to none at a junk yard. The module controlled blower speed using resistance. In the event it has failed, all you can do is bypass with a toggle giving you either high speed or none.

The other style is controlled by the bum (body control module-computer) which would need to be replaced if problematic.

Do not forget to check your owners manual not only for fuses, but fuse box locations if designed with multiple fuse boxes.

The problem with digital dashes was digital dashes. Yeah, they were neat, but plastic circuit boards broke causing variable displays to quit working.

If the dash did not light up at all, it could be as simple as a connector or a fuse, but you are telling me the fuel and temp are not displaying. You could check under the dash for a loose ground for the potential problem. You could also check the gauge fuse, but I doubt if it is bad for numerous reasons. I also doubt if you have a temp sending unit and fuel gauge sending unit bad at the same time.

Age, ambient temperature, driving over bumpy roads commonly cause problems in digital displays, because as I said, plastic circuit boards crack.

The best thing I could recommend to you, because you will find it very valuable in repairing anything on this vehicle is to go to EBay or Craig's and a brain a factory service manual for a 1991 deville/fleetwood. There you will find diagnostics to all problems big and small preventing changing good parts on a guess as so many do and find they wasted time and money and still did not fix the problem. The use of the manual will give you pin point diagnostics for your exact vehicle.

Let me know what you find.


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Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

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