Hey guys,
I've been the dreaded DSC trifecta light intermittently over the last 4 months. My symptoms are the following:
- ABS, BRAKE, DSC lights on
- Speedo working
- Cruise Control working
- "TIRE CONTROL INACTIVE" displayed in Kombi
Since then, I've replaced the two front wheelspeed sensors, but the problem has not gone away. I haven't replaced the rears because the speedo and cruise control functioning leads me to believe its either the front or the ABS module.
I'm tempted to get the module rebuilt, BUT these lights always go off after work when its no longer humid (live in SC). The lights pretty much are always on in the morning and are off in the afternoon. Am I looking at a failing module or is this something else? I don't want to just needlessly throw parts at the car.
As for diagnostics, I haven't been able to get INPA or EDIABAS reinstalled on my laptop, so I'm not really able to determine what the DSC error is from.
There has got to be someone near you that would read the codes and help you figure it out, but there is also a lot of diagnostic info on the web. Search for E39 brake (or ABS) trifecta and you should find lots of helpful info on diagnosis.
Thanks, I will try to find someone local to diagnose.
I've read through alot of the info available, but I haven't seen anything regarding the intermittent on/off due to moisture or possibly humidity. This is what I'm really asking...to see if anyone has seen behavior like this.
Humidity correlation leads me to guess at a wiring issue. Something cracked/split open that gets water in it, or maybe something just barely making contact. Have you inspected all relevant wiring to ensure no cracks or shorts?
mine was intermittent for a while, changed a right rear and front right sensor that the INPA showed faulty, worked ok after parked in heat or after a longer run with more engine heat soak, but now it's gone and the ABS unit needs work I figure
There is a separate code for a plausible fault vs. a short circuit and INPA can tell you either and exactly what wheel is causing it. Both codes can be totally intermittent. I had to replace both rears, one after the other- the wiring was falling apart to the touch after 15 years. The insulation just crumbled away in my fingers. As the wiring brushed together it would throw the code here and there. At a glance they can look OK but look closely at the wiring going from the car connector in the wheel well to the sensor itself on both rear sides. Betcha it's the same thing. No INPA required in that case, just a visual inspection.
Thanks. On my car (this is on the 540iT, not the M5 this time) I was getting an INPA error on the left rear wheel speed sensor. I obtained a used one but it was from a sedan so I had to lengthen the wires to make it work. The error went away but my GM is reporting lack of a speed signal so I'm not sure what could be causing that. Clearly the speed sensor must be working if the error is no longer present.
I'll dig around the GM itself and connector and see if I can figure it out. I'd love to get servotronic back up and running. The M5 steering box is heavy with 275 front tires and no assist at parking lot speeds.
I've had this intermittent problem before. In my case it is very intermittent. I'll have the trifecta on and off for a few days and then nothing for months. In that case I agree with above - it must be wiring since I can't see how a sensor failure will remedy itself for a prolonged time. I'm in SC but this was also happening in CT so I don't think for me it is a humidity issue.
I believe the problem with the ABS module is bad solder joints. They deteriorate over time. There is a DIY here showing how to do the repair. So intermittent faults might be the result, although in my case the trfecta would stay one once the car warmed up.
I would definitely go through the speed sensors first, as it is easier and cheaper. But it could well be the ABS module. Not a big deal, hardest part is getting it out (unless you have tiny fingers). Cost in the $200ish range. Good for another 10 years once fixed.
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