May 11, 2005
About 2 years ago, the ABS light started coming on once in a while when I started my 1995 Volkswagen Passat VR6 Wagon. Well, actually, the light always came on, but it should go off after a few seconds. What I'm talking about is the light not going off. This indicates that the on-board diagnostics found a problem during the ABS self-check. When this happens, ABS is disabled, but the brakes still function (hopefully) like brakes did for decades before ABS came along.
Over the course of time since this first started showing up, it has gotten progressively more frequent until about 3 months ago when the light would never go out. In California, where it hardly ever rains, much less gets icy or snowy, ABS is not that important, specially if you had already been driving for years on ice and snow in non-ABS equipped cars. Nonetheless, the ABS light is a nuisance, so I want to fix it.
First, I did a brake job. New rotors and pads all around. The only difficulty here was changing the bearings in the rear rotors. I had never knocked out races and re-installed them, so this required some learning. I was lucky that our local neighborhood car guy was around to ask him for advice. After he walked me through the steps, it wasn't all that hard (just a lot of pounding using a brass rod so as not to scratch the steel races).
During this process, I removed all the old brake fluid and replaced it with new fluid (DOT 4 on this car). This is important because over time, brake fluid will absorb moisture from the air. Changing the fluid will help prevent corrosion of the brake system from the inside due to this moisture. The old fluid was black. By the time I was done bleeding the entire system, the fluid came out a very weak caramel color. Hopefully that's enough flushing.
Anyway, this was a good opportunity to clean and inspect the speed sensors at each wheel. These remove easily - one allen head bolt holds in each sensor - they are mounted behind the rotor or wheel flange. Once you get them out, you can brush them with a old soft toothbrush sprayed with brake cleaner. This will get off any build up brake dust and since these devices are magnetic, a lot of metal dust from the brake pads builds up around the sensors (I believe these are Hall Effect devices, no?). Before cleaning, my cubic sensors looked like fuzzy black balls from all the buildup of metallic dust.
I inspected each cable for obvious signs of damage, and then re-installed the sensor before going on to the next wheel.
It turns out that this simple procedure did not fix the problem with the ABS light. So, I began to try some other tests. One thing that I've noticed over time is that whenever the ABS light stayed on, I lost cruise control as well. To me, this is a very strong indicator of the wheel speed sensors. So, I did a bit more to check them out. I seperated the sensor connector and put an ohm meter across the contacts going back to the cable (on the wagon, the rear sensors' integrated cables run up into the cabin beneath the rear passenger seats - this is the closest point to the sensors for taking a reading). The rear sensors displayed 1100 (+/- 2) ohms. Wiggling the cables did nothing to alter the reading. I've read various specs on these sensors, and 1100 ohms would seem to be very normal. I never got around to reading the front sensors, but I imagine they're about the same.
The reason I never read the front sensors is because 1. I suspected they were fine, and 2. I found something more probable while browsing the web for other ideas. As it turns out, Passats of this era often have a problem with their ignition switch. I guess the issue is that when the switch returns from the start position to the run position, proper contact is not always made with all of the switch terminals. I also read about people trying the "ignition switch trick" but not explaining what the trick was. I thought, why don't I give it a try anyway.
I started the car and returned the switch back to run, as I normally do - just by releasing it. OK, the ABS light stayed on. I noticed, though that there was some play in the switch torwards the "off" direction. I tried starting and releasing with a definite bias towards the off direction - no luck. I played with it a bit, then realized that if I released the switch slowly back to the run position, but kept a bit of tension on it so that it barely came back to the run position, that my ABS light went off! So, that's where I am. I will change the ignition switch if it continues to be a problem, or I will otherwise learn to manipulate it so that the problem does not show up.
If I need to replace the switch, I will search around for clues as to whether it's the barrel and key portion (mechanical) or the electrical portion. There's no need to re-key all the doors if I only need to change the electrical portion, and together, they run about $100.
(78,400 mi)
tags:cars, passat, volkswagon
posted by alain on Sep 13, 2005
hello man, just read you stuff about the passat, i do have the same kind a problem on mine ( 99 passat 1.8 turbo), do you mind to chat by email about it please ? ty alain ps : alain_labaisse@yahoo.com