Computer Glitch - Benzworld.org

Shipsake · 01-10-2007, 01:18 PM

Randomly and unpredictably and in no discernable order my (ABS) light, (TCS) light and speedometer will come on and off. Sometimes when the speedometer is reading zero (and I know Im doing about 70) the yellow exclaimation point will flash and the speedometer will start working again. Sometimes I go somwhere and everything works without a sign of a problem. Other times the ABS and TCS light come on together and the speedometer continues to work.

What should I replace, where can I get the part? It's certainly not an engine ECU as it is a mechanically controlled DIESEL... HELP???

**Musikmann** · 01-10-2007, 01:22 PM

In my experience, intermittant problems, unless they can duplicate them of course (regardless of the car), are next to impossible for even the most seasoned techs to figure out. Good luck!

Shipsake · 01-10-2007, 02:25 PM

True, very hard to replicate.. This is why I need someone to identify which computer module controls these functions, what its called or a part number and where I can get one. I'm just going to replace the module, not try to fix anything...

**Matt L** · 01-10-2007, 02:35 PM

Could this also be caused by bad wheel sensors? The function for these is almost certainly in either of the PCM or the combination control module N10-1. You don't want to replace either of these unless you know it to be bad.

Shipsake · 01-11-2007, 07:24 AM

Thank you for your thoughts. I thought about the wheel sensors too but how would that affect the speedometer; isn't the speedometer information derived from the transmission? One other point; one the computer senses a bad wheel sensor doesn't it shut off the ABS system until the sensor is replaced and someone resets the computer - in my case it goes on and off.

**Matt L** · 01-11-2007, 11:52 AM

The speedometer is driven by the ABS sensors alone.

I don't know about needing to reset the computer.

Shipsake · 01-12-2007, 07:21 AM

Matt, thank you again. Well, if it is true that the speedometer derives its info from the ABS wheel sensors then it is entirely possible this could be the problem but one more question, how can the speedometer be independant of the ABS and TCS then; meaning, if those lights are on, it is not always the case that the speedometer does not work. Is there any way to determine which speed sensor is defective - can they be tested? Where can I buy them; dealer only?

**Matt L** · 01-12-2007, 08:05 AM

I'm quite sure that a code would be stored for this. You need to find someone with an appropriate scanner for the car (STAR tool). I'd probably start by checking the output voltage.

I'm not sure how the speedometer derives the speed from the wheel sensors, just that it does. I do know that the speedometer shows zero if you spin the rear tires while in place, so the front tires do not turn.