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sprinkles08
sprinkles08, ASE Certified Technician
Category: Cadillac
Satisfied Customers: 22114
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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I am working on a 1999 deville it has a theft deterent

Customer Question

I am working on a 1999 deville it has a theft deterent system problem, abs light on radio and heater dosent work after car is started it has correct voltage to radio and heater fuses in fuse box in the truck but neither work. I tried doing a vats bypass with resisters but it didnt correct the problem. Do you have any ideas I could also use the schematics for the RAP system and VATS system and the location of RAP relay if this vehicle has one I kinda suspect the problem might be there.
Submitted: 7 months ago.
Category: Cadillac
Expert:  sprinkles08 replied 7 months ago.

Hello and welcome to JustAnswer!

You most likely have a handful of unrelated problems going on. It sounds as if you may have a bus communication problem though, which could be wiring or an internal failure in any module.

If there is power to the radio fuse and the radio doesn't work then odds are the radio itself has failed. It would need to be removed to test it's powers and grounds to know for sure there was a wiring issue or the problem was in the radio itself.

What is the actual problem you believe is a security related issue?
What is the exact problem with the heat?

Do you have a scan tool capable of communication with the ABS module?

Customer: replied 7 months ago.
It took me ahwhile to buy a abs scanner and no it wont communicate with the car at all just like the code scanner wont., I tested the class 2 communitcation line for shorts to ground there are none how can i find out what module is at fault without being able to get codes from it?
Expert:  sprinkles08 replied 7 months ago.

Communication isn't possible with any module?

Customer: replied 7 months ago.
no it just respondes with a unable to communicate with vehicle
Expert:  sprinkles08 replied 7 months ago.

The bus has to be shorted low or high if no communication is possible with any module, or the circuit is open between the data link connector and every module. You can check for continuity between the DLC and modules if ok then you either have a wiring problem or module shorting the bus high or low. You can try unplugging modules one at a time to see if communication with the rest will resume.

Customer: replied 7 months ago.
I pulled each of the three main modules and checked to see if i had continuity between them and i can get less than a half ohm resistance between the pcm and any of the other modules like the bcm i just dont get it lol
Expert:  sprinkles08 replied 7 months ago.

You either have a module or wiring issue pulling the bus high or low.

Customer: replied 7 months ago.
I also chked continuity between the dlc and the pcm it was ok
Expert:  sprinkles08 replied 7 months ago.

You either have a module or wiring issue pulling the bus high or low.

Customer: replied 7 months ago.
if i pull the other modules not the pcm one at a time and i at least get communcation back it will setg codes but at least tell me which one is at fault right?
Expert:  sprinkles08 replied 7 months ago.

If you can unplug a module and regain communication with the rest then that module is the cause.

Customer: replied 7 months ago.
Ok I will try that tonight and let you know asap thanks
Expert:  sprinkles08 replied 7 months ago.

You're welcome!