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Cadillac Repair/1990 Cadillac de Ville ABS Trouble


QUESTION: Re > 1990 Cadillac Sedan de Ville with an “Anti-Lock Braking System” (ABS).  I bought the car used a few months ago (early 2013) with only 32,000 miles on it.  (The original owner passed away about 15 years ago and the car was parked in an indoor garage since than.)  With the exception of a problem with the brakes, the car is in otherwise very good condition.  When you first step on the brake pedal, the dashboard “Brake” warning lights (there are two of them, one red, the other sort of orange colored) light-up indicating a problem with the braking-system.  However, as you continue to step on the brake pedal, both lights go out almost immediately, and the car will come to a stop, but not as “smoothly” as it should.  I pulled the front wheels and visually inspect the rotors and pads, but there was still plenty of useful life left in them, leaving me to believe that the problem lies with the Anti Lock Brakes Master Cylinder / Power Booster.  Any suggestions would be appreciated… Thank You

ANSWER: Hello,

This was the first year of the anti locks on the De Ville and they came with a whole host of issues. I no longer have the manuals I received at GM school. Thse have module issues and GM commonly used their piece f garbage hydro boost that in the mid eighties was restricted only to dieseld because of the diesel not producing vacuum.
I have had my share of issues with hydro boost on my last 1999 Suburban (thank God that one is out of my life!) I had a noisy steering pump. That's it! went through 4 more and 2 hydro boosts until it would stop at times and other times no brakes, no steering!

Hydro boost is not the round vacuum cylinder that the master mounts to at the firewall. Instead it is a rectangular pump mounted above the driver's inner fender with lines feeding to the power steering unit. In other words, you could be opening Pandora's box here if you find you need to replace this unit. It is easy enough to tell the difference. Just send me a picture of the driver's side fire wall and I will tell you what you are dealing with. The purpose of a booster is brake assist. If the pedal seems somewhat spongy or the brakes fade and the rotors are not glazed over, I woul consider the possibility of a bad hydroboost.

The modules were known for failure in the 90's GM, in fact my Intrigue has both brake lights on, however it does no effect stopping ability and I have driven it 10,000 miles that way. A rebuilt module is about $500.00.

The first thing I would highly recommend is try to obtain a Cadillac factory service manual from Craigs or Ebay before you begin your diagnoses and start changing parts on a guess.

I know this was not the exacting answer you were looking for, but there is nothing that can be guessed on with this brake system that was introduced in 1990.

---------- FOLLOW-UP ----------

QUESTION: +++++++++++++++++++++++++++++++++++++++++++++++++

Hello Rob Painter…

About three (or so) weeks ago you were kind enough to respond to my inquiry regarding difficulty with the Anti-Lock-Brakes, Master Cylinder/Power-Booster on my 1990 Cadillac deVille.  

At that time you advised me that you thought that the trouble appeared to involve a problem with the vehicle’s “Hydro-Boost” assembly, but that I should send you a picture of the driver's side fire wall, with the hope that you would then be better able to tell me what it was that I was dealing with.  

Sorry that it has taken this long to get back to you, but attached please find some photographs of the driver's side fire wall as you requested.  

Furthermore, please note that (to date) I haven’t experienced any difficulties with the Power Steering, that the rotors are not glazed over and that the Break Pads are in good condition.  

Hopefully this is enough additional information for you to help me resolve the malfunction, and I thank you for whatever help you might be able to provide.  



s most
I guess the may be a miscommunication issue on my part. When you say that the car does not stop as smoothly as it should, I took it as extra force required to stop the car. I reread you complaint and if you are having like a pulsing when you apply the brakes, the rotors most likely need cut or replaced. As for the lights, that is most likely an ABS module issue. Very expensive to fix, however if the car stops fine and the pedal buzzes when stopping on wet pavement, its really nothing to be concerned about unless you want to spend over $500 so the lights don't come on.

This is not to be confused with a systems check that is done each time the engine is started. The lights will come on for a couple seconds and not come on again. I did not receive photos and if you sent to, they could have gone in my spam folder.

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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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