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I have a 86 caddy sedan deville, my ECM buttons all work but the display never changes. Its showing -188* and all symbols displaying. Its as if the display is stuck. Like i mentioned, all button controls function properly but the didplay never changes. Therefore, i wont be able to read codes, etc.. What should i look for first to correct this problem?? Thanks in advance


What we are dealing with is very old electronics. When I say that is that you are dealing with plastic circuit boards that expand and contract in severe cold and severe heat. Couple that with vibration from crummy roads and circuit boards crack.
These plastics were never designed to last 30 years. We had them fail when the vehicle was new!
My guess would be the display unit, but if you don't want to go with a guess, I suggest  acquiring a factory service manual. You should be able to find one for $100 or less on EBay or Craigslist. The manual has diagnostic flow charts for diagnoses and it will help you in the future for other problems. Without it you are working in the blind which can be frustrating and expensive.

As for the codes, there are scanners that will read the diagnostic codes. The system was very primitive and the codes are very general and the standard used in today's vehicles  wasn't implemented until the 90s. In the newer system OBD II a problem in the computer system can be pin pointed. On your system, you can only display a circuit that can have so many issues in it and very difficult to diagnose.
Again, that is why you need the service manual.

In the event it is the display, you will have to go used and hope there aren't issues with it.
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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