ABS activating when stopping slowly

[nathanncnm]

Ok, I have a 07 Trailblazer ls with 4 wheel drive with the 4.2. I am having issues with the abs kicking in under 10 mph. I pulled the following codes: C0045, C0245, C0455, C0131, C0244.

Can anyone interpret these codes to form a possible diagnosis. I know one of the codes is for a left rear speed sensor. I know there is far more knowledge on this board than I am going to figure out on my own. Just cant afford to throw money at possible solutions when someone may have had this issue before.

 

[Wooluf1952]

Welcome

In case you haven't heard:
http://gmtnation.com...eres-the-story/

IIRC, if one of the front wheel bearing is going bad, it can cause the ABS to activate.

 

[Sparky]

C0245 could be triggered by C0045 as losing a wheel speed sensor signal could just freak out the entire ABS system. Although, C0131 is complaining about the ABS pressure.

C0455 is complaining about the steering position sensor, and that can possibly trigger C0244. Sometimes all that is needed to get Stabilitrak angry is to park with the wheels cranked.

As Wooluf1952 said, a flaking out ABS sensor on a front wheel can trigger low speed ABS firing. I'd get that fixed first (usually if the sensor is firing the ABS like that the hub bearing is probably getting close to being worn out and making noise anyway) and see where that gets you.

 

[Mooseman]

Seems like a lot of codes if it would be just one wheel sensor. The Stabilitrak codes could be coincidental to the ABS issues since both are tied to each other.

It could be the rear wheel sensor causing the ABS to activate without cause. This usually happens with bad sensors or or hubs in the front but a bad rear sensor could also do that I guess. C0045 says there is something with the left rear sensor. Try disconnecting that sensor and take it for a drive. You will probably get more codes (or maybe less) but this should eliminate the low speed activation (ABS should be disabled now).

 

[hockeyman]

Can the sensors on these trucks be removed independently, or are they sealed within the bearing? I've replaced both of my front wheel bearings before, but forget if the sensor was removable or not...

I had some sensor/code issues on another one of my cars a few years ago. Turned out that one sensor was just dirty. I removed and cleaned all of them with some lacquer thinner, and the codes went away.

 

[HARDTRAILZ]

sensor is removable. I keep spare wires. I had a couple ripped on trails over the years

 

[nathanncnm]

Thanks for the input guys, i really appreciate it. So I cleared all the codes before work and have done about 50 miles of driving. When I checked the codes this evening, the only one listed is C0455 pertaining to Steering Wheel Angle Sensor Performance. Would this cause the issues that I am having with the ABS? Doesnt seem like it would but what do I know. I am still looking around to see if I can get someone with a good scanner to read the live wheel speed to check the sensors.

 

[xavierny25]

I'd really have to point to the wheel hub for the abs issue. I replaced my brother-in-law front 2 hubs do to abs kicking in at highway speed. It's was pretty scary for him when it kicked in and almost put him to the center divider. Not that the system is any different between models but his is 2008 tb ss with awd.

 

[07TrailyLS]

Steering wheel position sensor needs replaced. Common symptoms are abs light, service Stabilitrak system light and your traction control light will be on as well because Stabilitrak isn't active. I've never heard of it actually causing your abs to activate though.

 

[Mooseman]

Common symptoms are abs light, service Stabilitrak system light and your traction control light will be on as well because Stabilitrak isn't active.

I've had issues with my SWPS and never has my ABS or Traction Control light come on or had issues with them.

 

[rcam81]

I have an 07 TB. I was having the same issues for the last month with the abs kicking in. Both of my front hubs were replaced 2 years and 17000 miles ago. They were replaced with Timkin brand hubs. I ended up replacing the right front one again last week . The bearing was full of corrosion and causing the ABS sensor to get a false reading. Warranty covered the cost of the bearing replacement.

 

[Meatsloth22]

I drove around for at least 2yr with a bad bearing and the abs problem. Fixed it last year now everything is fine. I wouldn't suggest driving around on bad bearings very long.

 

[freddyboy61]

Before changing out the hubs, try cleaning the mounting surface under the speed sensor. Sometimes rust builds up under them and raises the sensor just a tad and that can make for a weak speed signal back the ABS module.

 

[Robbabob]

I bet you notice this when babying the stop. Harder stopping doesn't. You can remove and clean the sensor, and inside the hole.

Let us know how this goes.

 

[mcewans]

My Experience

So I had the same issue with my ABS activating at low speeds on my 2004 trailbalzer. I saw the writeup at it stated that you need to have at least 450mv with the wheel spinning at 1 rev/sec. I don't know if this make a difference, but I used a Fluke DVM that measures true RMS for the AC signal. When I started out, I removed the calipers, pads and rotors on each side and disconnected the ABS sensor from the connector and hooked up the DVM. I did check the resistance of each senor and I was getting around 1050 ohms on each side. For whatever its worth these were AC DELCO parts. At first I was getting a signal of around 60-80mv on each sensor. After removing the shim on each hub and cleaning the rust off the opening, the signal went up to 100-150mv at 1 rev/sec and around 280-300mv with me rotating the wheel as fast as I could. I even checked the signal at very low rotation for spikes and I was getting around 28-30mv from just barely turning the wheel. More important was that the signal was consistent on each wheel. I don't know where the 450mv signal threshold was obtained or what kind of AC signal it is referencing to whether its peak to peak or RMS. I know if you use a "cheap" DVM VS a Fluke with RMS, I am guessing that you will get a different reading. I know that there is a similar issue with the ABS sesnsors on the older Chevy Silverados and that threshold was 350mv. I am curious how these readings were determined, because my meter is reading much lower readings, but the ABS activation on low speeds is not longer an issue on my Trailblazer anymore.

 

[nathanncnm]

Finally figured out my issue this past weekend. It was the wheel speed sensor. Figured out that I could view a live graph of the wheel speeds using a bluetooth adapter and Torque Pro on my phone. Saw the driver side wheel speed having some odd readings in comparison to the other wheel speeds so I replace the wheel hub. All is good with that. Now on to the lower ball joints, sway bar links, and all 4 shocks.

 

[HARDTRAILZ]

Good info and glad you got it fixed!

 

[freddyboy61]

I believe the 450mV measurement is when taken with an oscilloscope and it is a peak-peak value. Don't know what the minimum level is for proper operation. I know that when I measured mine before cleaning the mounting surface, it was well below 450mV P-P.