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-   -   ABS Troubleshooting (http://blazerforum.com/forum/2nd-gen-s-series-1995-2005-tech-41/abs-troubleshooting-80997/)

Toby Hanson 08-09-2013 02:02 AM

ABS Troubleshooting
 
This has been quite a week for my '98 Jimmy. Sunday I canceled the family vacation to return home and replace the right front hub. After replacing the hub the ABS light came on. I drove it that way a couple days. The steering was better but there was still some wander and also some growling noise. Wednesday I drove to Seattle and back and the growling got worse. The left hub needed replacing also. This morning I replaced the left hub. Now it steers properly again and the growling is completely gone.

The ABS light is on and it's acting up now. I used quality Timken hubs for replacements and they each came with new sensors and wires. As soon as I installed the first one (right side) the ABS light came on. I replaced the left one before I checked the ABS codes. The wire for the old left sensor was cut along its length and taped up.

After installing the new left hub and sensor I pulled the ABS codes: C0221, C0223, C0225, C0226, C0227, C0235, C0237, C0281. I cleared the codes and drove the truck. The following codes came back: C0221, C0227. Per the diagnostic procedure in the factory shop manual, I checked the resistance in the sensor circuit at the EBCM connector. It was WAY over spec. Spec is about 1330-1900 Ohms; the circuit was testing at about 30 kOhms. I tested the circuit again at the wheel speed sensor harness connector down by the wheel and it tested at 25 kOhms. According to the diagnostic chart that's still way too high, meaning the sensor was bad. I took it out and returned it to AutoZone. They gave me a sensor off a new hub. I checked the resistance of the new sensor before I installed it and it tested within spec. I installed it and the code C0221 went away.

I did another test drive and cleared the codes and a new code set: C0223. I drove the truck around in the evening and the ABS would kick in whenever I would stop and the speed dropped below about 5mph. After that happened several times the ABS light came on again and after that happened the ABS stopped kicking in.

I still have more troubleshooting to do in the coming days. In the meantime I have a couple questions: why would the ABS problems start when I installed new hubs and sensors? That doesn't make any sense to me. The warranty replacement sensor came with three thin metal shims. I used all of them when I installed it. Is that normal like on older GM starters?

Any insight is appreciated!

08-09-2013 08:15 AM

Hey Toby, lets look at it like this, we have a hall effect switch. When the hub is spinning its putting out X amount of juice, when it drops the abs sees it and turns on correct?
My guess would be with too many shims its not reading enough voltage and turning on the abs.
I know there are some TSB's on this exact problem. For now why don't you pull shims till it's just not touching anything and see what happens.
The thing works on such small voltage variance that it's a PITA.

Reason for three shims would be adjustment right or they would just give you one of the proper size?

I think I heard that with your machine on live data you might show mph with the thing standing still.

As far as the abs after awhile not kicking in, my guess would be there has to be some kind of a default over-ride.
If the sensor were to go bad the computer would have to have a way to lockout the abs so it's not on all the time.

Captain Hook 08-09-2013 08:19 AM

Most likely it's because the sensor is too far from the tone ring, (using too many shims). If it's too close to the tone ring, the tone ring will shear off the end of the sensor. This is why sensor replacement alone is not recommended, replace the entire hub assembly.

This TSB explains why you're having low speed activation. http://ww2.justanswer.com/uploads/GM...s_bulletin.pdf

Toby Hanson 08-10-2013 01:23 AM

So far everything in both responses makes sense. The original right hub that I replaced had a bad sensor. It did not have any shims. The replacement sensor that I put on the new hub has the shims. Since I was in a hurry I installed the new sensor with the shims to make sure the sensor didn't hit the reluctor ring. I'll do more troubleshooting and testing next week when I have some time.

Also, Spitty's exactly right about the scanner showing velocity while standing still. My scanner shows 3mph when the truck is sitting still in park. On the ABS data stream page it shows 4WD status as well. Regardless of whether it's in 4WD it always shows 4WD status as inactive.

Thanks for all the info. It's a big help.

Toby Hanson 08-11-2013 01:48 AM

Problem solved! It was the shims on the wheel sensor. I read the resistance and the voltage on the sensor with the shims in. It was out of spec. I removed the shims and read the resistance and voltage again and they were perfect. I put the wheel back on and took it for a test drive. Everything functioned properly and there were no codes.

Everything on this truck needs to be fixed twice. I am getting very tired of that.

08-11-2013 08:13 AM

It's all part of the charm.

Toby Hanson 08-11-2013 10:20 PM

Quote:

Originally Posted by spittybays (Post 596495)
It's all part of the charm.

I like your use of the word "charm." :icon_angel:


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