Trac Off and Anti-Lock Issue

[57j2olds]

Hello,
Earlier this year I had the issue with the Trac off/ABS lights illuminating on the dash. More a nuisance than anything. I discovered that it was a bad connector at passenger front wheel bearing. Easy fix.

Well, its happening again, only a bit different.

My scanner says a failure or open circuit at Front Left (Drivers side I assume). I hooked up my ohm meter to the wheel bearing connector and it read resistance. Then I spun the rotor and resistance changed. This tells me the bearing connector is OK.

I replaced the connector anyway to eliminate possible issues.

I can disconnect the connector at the wheel bearing, plug it back in, start the car and NO warning lights.
The second I put the car in gear from Park to Drive or reverse, the warning lights come on. This is very repeatable. I can drive to work with the warning lights on; turn the key off; start the car again and NO warning lights. The second I put it in gear the warning lights come on.

Any clues?

[Jason H.]

Did you ever find a solution to this issue? I just changed my hubs, yesterday, and am having the same exact problem. No lights until I shift to either 'drive' or 'reverse' from 'park', and then they come on.

[96 SSEi]

it could be that the system only engages in drive gears.

did you check the wires to the plug on bearing - see if you get good continuity.

[ddalder]

I assume you replaced the hub(s) with new? Lots of people get them at the wrecker and since it's not an uncommon problem with these cars, used may be no better than the original. If they are new, I'd be looking at wiring first (just because it's cheaper than starting with component replacement, and should be checked anyway), then the possibility of a fault with the EBCM. If I'm not mistaken, they have been known to develop bad connections internally resulting in these same failures.

Measuring the hub with an ohm meter really isn't the best test since a short in the coil will still suggest it's intact. You should spin it and measure it with an AC volt meter. Photobucket isn't being very helpful in linking the video I made a few years ago. I know Andrew posted it a while back somewhere on the forum, just can't remember where. Anyway, I used a drill to spin a hub and measured about 750mv. This can vary up and down depending on the speed the hub is turning at.

The following is really when a fault is detected in one of the rear wheel speed sensors, however it'll probably just be a matter of time before you're looking at this as well..

There is a connector under the rear driver's side of the vehicle that connects the rear wheel speed sensor wiring harness to the main body harness. There have been several instances reported of water intrusion into this space. In some cases there are only corroded terminals, but there have been multiple cases where moisture has wicked into the main body harness so far that wiring had to be replaced as far as a couple of feet in. When this happens, it's also likely that the wheel speed sensor wiring harness needs to be repaired or replaced. I always recommend checking this connector for the problem reported here. Since it's outside the vehicle, it's critically important to ensure it's very clean and dry before separating it, then making sure no dust or other debris contaminates the seal or mating surfaces when it's reassembled. These are weatherproof connectors, but with the location, age and heat, care is necessary to ensure they aren't compromised any further.

Of course, DTC's are always very helpful!

[Jason H.]

it could be that the system only engages in drive gears.

did you check the wires to the plug on bearing - see if you get good continuity.

Yes, I gave a quick inspection and did not see any issues prior to installing the new hubs. There were no idiot lights on the dash before I did the job and I was extremely careful with them during the process of changing old to new. I guess it is a possibility that something happened to these 19yr pigtails. How do I check for continuity? Ohmmeter on each terminal of pigtail coming from car?

[Jason H.]

[quote="ddalder"]I assume you replaced the hub(s) with new?

Measuring the hub with an ohm meter really isn't the best test since a short in the coil will still suggest it's intact. You should spin it and measure it with an AC volt meter. Photobucket isn't being very helpful in linking the video I made a few years ago. I know Andrew posted it a while back somewhere on the forum, just can't remember where. Anyway, I used a drill to spin a hub and measured about 750mv. This can vary up and down depending on the speed the hub is turning at.

Yes, they are new assemblies.

Testing the volts will show if the new hubs are bad? If I take...say...a hard-wire wheel to the side of the hub and spun it with the drill (if there is a better way, please tell me), what do think is a good tolerance level of mV? 600-850? What do you think would be too low of a value showing that the hub is bad?

You guys have some good info...it is appreciated.

[ddalder]

Using a wire wheel on a drill is how I spun the hub. Keep in mind that a new hub will be pretty tight compared to one that has some kilometers on it (since I'm in Canada lol). You may find it hard to spin with a drill. I was able to achieve about 750mV consistently at the speed my drill could spin at, but this will vary. Short of using a scope to actually look at the waveform (which is preferred), this will at least provide confirmation that it's generating some type of signal. Because of the way they work on these vehicles (newer vehicles can vary), they produce a small AC signal that changes in frequency and amplitude with speed. The problem with measuring resistance is that it only confirms there is continuity in the coil. There are other problems that can include an excessive air gap in the sensor, broken teeth on the tone ring (also known by some other names) or debris.

In the video below, the section between times 1:40 to 3:47 offers a little information on how the system works and testing.
https://www.youtube.com/watch?v=cGwjonIQaXc

A meter is not nearly precise enough to pick-up signal variations for something like a broken tooth or two, but as I said, it tells you that there is some signal being generated.

If your hub(s) are new, it's not impossible, but very unlikely your problem is there. I'd probably start with the other potential issues.

[Jason H.]

Thanks, ddalder!