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Frustrating ABS/TCS Problem on 1999 Seville STS


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Hello All! Thanks for checking out my post. I have a frustrating Anti Lock Brake (ABS) problem on my 1999 Cadillac STS that I soliciting advice on how to diagnose.

First, a little history about myself & my car. I am a former chassis GM engineer (1998-2008) who worked in vehicle design & development at the GM Tech Center in Warren. I did not work on the development of this vehicle. However, I have access to a GM’s service manuals and some diagnostic tools. My car is a 1999 Cadillac Seville STS that was purchased off-lease by my mother in 2001 (at 24K miles). She drove it daily and had dealer maintained until 2007 when I bought it (102K miles). The car’s full service history is known and it has been very well maintained. It currently has 117K miles.

Starting at 58K miles when my mother owned it, it would occasionally set both the ABS and Traction control light (maybe once a year). It would set an ABS code; usually C1243 Brake Pressure Modulator Valve (BPMV) Pump Motor Stalled. My mom would have the dealer look at it, then would read the code, then clear the DTCs and everything was OK. However, at just over 100K miles it started setting the code more often, as bad as once a week. Her dealer thought either the Electronic Brake Traction Control Module (EBTCM) or the BPMV were bad and recommended both components be replaced. This is when my mom bought her current Cadillac SRX and sold the STS to me.

For 6 months (November – April), the ABS and TCS lights never came back on. Everything was fine. Then after April, the light came on occasionally. It come on only at startup, and within 1 mile the light goes out. The strange thing is that when the lights are on, the following items do not work:

· Heated seats

· Rear window defogger

· MagnaSteer

· Compass on mirror & auto dimming feature

· The fog light switch does not work. If the lights were off, they stay off, and vice versa.

· Forced 2nd gear starts (probably due to the TCS light being on).

I started really looking into the issue in August. I borrowed a Tech 2 and retrieved the following codes from the ABS module on 8/22/2008:

· C1234 LR Wheel Speed Sensor short or open circuit

· C1255 EBTCM Internal Malfunction

· C1255 E2 Internal Malfunction

· C1298 PCM Indicated Class 2 Serial data link malfunction

I cleared all codes, and drove it to see what would reset. On 9/19/2008, the following codes were retrieved:

· C1255 EBTCM Internal Malfunction

· C1255 E2 Internal Malfunction

· C1298 PCM Indicated Class 2 Serial data link malfunction

· U1016 Loss of PCM communications

· U1056 Loss of RTD/RSS communications

Thinking the EBTCM is bad due to all the internal faults, I swapped the EBTCM with a used one from a 1998 car (direct replacement according to my local junkyard). All codes were cleared on the vehicle. I still get the lights coming on with increasing frequency. I scanned the car today (12/7/2008) and receive the following codes:

Powertrain Control Module (PCM):

· P1602 Loss of EBTCM data

· P1644 Torque Control Delivered, Torque Output Circuit

Supplemental Inflatable Restraint (SIR):

· U1255 Generic Loss of Communication

· E1040 Loss of EBCM/EBTCM communication


· C1298 Class 2 data communication link malfunction (set twice)

Suspension (RSS):

· C1783 ICCS2 Data link left short to ground/open

· C1785 ICCS2 Data link right short to ground/open

Since I do not see the EBTCM internal malfunction codes anymore, that leads me to believe the used EBTCM is OK and there is come sort of communication issue with the car. A buddy of mine who worked as an ABS calibrator for Delphi feels it is a a communcation issue, as other Class 2 items (heated seats, rear window defogger, etc) are not working. He stated that BPMVs rarely every go bad. My local dealer (different from my mom's dealer) wants to replace both the EBTCM and BPMV.

Has anyone else run into this? I am running out of ideas on what to do. It is ruining the pleasure of driving this car. Any help is greatly appreciated.

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This sounds like a corroded/oxidized connector or chassis ground condition to me. You did not indicate where the car is located but if you are in the rust belt, I would recommend some labor intensive chassis wire harness inspection/cleaning as the next systematic step.


Drive your car.

Use your cell phone.


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  • 1 year later...

I feel for you. I have a 2001 sts....same thing happening abs, brake tcd come on at start up sometimes, when they do they go off sometimes after about 5 minutes. If you turn the car off and restart sometimes they go off. when the abs and brake are on I have no heated seats, fog lights, can't change heater settings. Went to the dealer and they checked with scanner and said no codes, drove around for most of the day and finally they showed up when I started the car. Went back to the dealer and he couldn't get the scanner to even read off the car, says now that I need a new PCM $1300 and that might not be the problem. Also can't return this part even if it isn't the problem, I'm not impressed. I went home and got error codes using the car's dash buttons. If I find out what the problem is I'll be sure to let you know. A while back Had it to the same dealer and we got it figured to bad ground but they didn't have time to fix it and I never went back. Going back tomorrow with codes that "I" pulled off the car that their scanner wound't.

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vmax: Likely, they don't have a working Tech II. Go elsewhere.

-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
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Yes, I was Jims_97_ETC before I changed cars.

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my bet... Ignition switch.

My car had the leveling computer intermittently (and then permanently) fail.. followed by the ABS system intermittently failing... A few back probing of a few relays confirmed that were you would expect 10V (or more ) I would only find 8V enough to work some things but not enough to trigger a normal code.


Easin' down the highway in a new Cadillac,

I had a fine fox in front, I had three more in the back

ZZTOP, I'm Bad I'm Nationwide


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WOW, I completely forgot about this post. I should have updated it when I solved the problem!!

The root cause of the problem was the ignition switch. I had the ignition switched replaced about a year ago, and all is well. OnyxSTS, my issues were just like yours, and when I saw low or no voltage on IGN3 circuits in the rear relay box, I knew it was the ignition switch. Apparently, the contacts for IGN3 circuit wear and causes the issue.

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I also had a problem with the ABS/Traction message on the dashboard, but i went away after replacing the battery!

So its a good idea to check your battery if you have these messages onboard!


Roger Martinsen

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