ABS issue development - C0035/C0040

[WarGawd]

So as per the subject, I've been dealing with an ABS issue that seems to be getting progressively worse. When it started, I had pressure washed all the recent snow, salt and grime off that day, and I assumed I had gotten some contact wet and it might resolve itself. So I watched it a day or two. My scanner doesn't have the ABS module, so I got Onstar to give me an ODD and they came back with the C0035 (front left sensor)

Over the next couple days I tried to pay attention to the conditions that resulted in various behavior. Sometimes it would do one thing, other times slightly different behavior. Then it warmed up a couple days, the ABS light cleared itself, and I figured my original assumption was correct.

But then it returned. Very low speed light brake pressure application would trigger the ABS when clearly there was no loss of traction. Then it got a bit worse, and I could hear the ABS cycling while just driving, with no brakes applied. That evolved eventually into the warning light (red circle with "i") accompanied by the warning chimes and a DIC message saying "Service Brake System". Onstar ODD now was giving me the C0035 plus a newer C0040. At this point, the warning light and the ABS light would both clear themselves shortly after startup on most ignition cycles, only to return as soon as I thouched the brake pedal.

Brought in to a friend (highly qualified custom bike builder Mike Haufe of XXX Chopper Works) we got it on the hoist inspected wiring, connections, ground tab - no issues observed. ABS connectors unplugged at wheel cleaned and reconnected. No change in behavior. His high end scanner was "visiting" elsewhere, so we couldn't go any further at the time.

One of the first things Roadie ever mentioned to me on this site was that at my mileage (bought July with 170,000km, now at 190,000) and with unknown service history, replacing hub assemblies in Spring might be up for serious consideration. Mechanic seems to think front left hub assy looks newer & has been replaced once before.

A thread on the OS with fairly identical problem description says the issue was resolved by pulling the sensors, and cleaning some stainless steel strip with a dremel - I'll track down a link later, but it didn't have pics, so I couldn't get a good feel for the process - anyone familiar with this?

So at this stage, while I look for a chance to pull the wheels and measure sensor output voltages, I thought I'd get some feedback here. Any thoughts on the above, weigh in please. Also, wouldn't mind hearing opinions on whether I should just do the sensors or just skip that and do the whole hub assy with integrated sensors. REALLY need some feedback on which brand hubs, country of manufacture, pricing, sources etc etc...

Thanx folks

 

[CaptainXL]

Well my hubs are doing exactly the same thing. Slow speed engagement of the ABS. Pretty sure it's the hubs. Toner ring and sensor are integral to the hub. I don't believe they can be removed. Remove the ABS fuse under the hood to stop it from pulsing. Going to replace my hubs next year.

But you can try the procedure someone on trailvoy did.

Just type "trailblazer slow speed abs" in Google. It's the first search result that comes up entitled "Simple Fix for ABS..."

 

[WarGawd]

Well my hubs are doing exactly the same thing. Slow speed engagement of the ABS. Pretty sure it's the hubs. Toner ring and sensor are integral to the hub. I don't believe they can be removed. Remove the ABS fuse under the hood to stop it from pulsing. Going to replace my hubs next year.

Yeah I'm kinda leaning towards the whole hub, but since I have no other indication that they are really a problem, I may have cheaper options to consider.

I want the fuse in for now to continue characterizing behaviors, but yeah I'll pull it (them? #33 AND #34?) when I need to.

Here's the link to the sensor removal & cleaning thread on the OS...I admit I don't fully grasp what he's doing without some pics. Simple Fix for ABS Wheel Speed Sensor - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum In particular, his comment "To make a long story short, rust builds up under the stainless steel strip, causing the sensor's gap between magnetic pickup and the hub's teeth to increase, which reduces the voltage output." has me thinking that when I do measure voltages, I'll be able to tell if his suggested resolution may apply in my case.


OH, Mods - I forgot there was an actual Brakes forum - move this as you see fit

 

[WarGawd]

and again today with the slightly warmer weather, the ABS system mostly behaved as expected. Codes cleared themselves after first couple ignition cycles, stayed cleared all night. ABS activated on icy patches when loss of traction occurred, but not otherwise.

Is it possible that colder weather reduces sensor output voltage towards some lower threshold where problems start?

 

[WarGawd]

Cold weather doesn't seem to be the cause, ABS system has operated flawlessly with ZERO issues for the past 3 days, despite temps of -14 to -28 deg C. Not sure what to make of this.


NOBODY has any fresh opinions on sources/brands of hubs, in case I DO need to change them?

 

[CaptainXL]

Cold weather doesn't seem to be the cause, ABS system has operated flawlessly with ZERO issues for the past 3 days, despite temps of -14 to -28 deg C. Not sure what to make of this.


NOBODY has any fresh opinions on sources/brands of hubs, in case I DO need to change them?

Timken seems to be the OEM from the factory so I would go with them. Can't remember his name but someone has a Timken on one side and a Moog on the other. He is doing a reliability test of sorts. They are both the same price (around $159). In any case I would make sure you get an alignment after replacing them or they could be short lived as I have read.

 

[WarGawd]

No further issues since last report, flawless operation of ABS under all conditions. Starting to think my original conclusion was correct after all, all I can do is keep an eye on it.

 

[WarGawd]

No further issues since last report, flawless operation of ABS under all conditions. Starting to think my original conclusion was correct after all, all I can do is keep an eye on it.

Not a thread bump, just tracking info - STILL has been no re-occurrence of any issues, despite all kinds of the crappiest conditions. Does anyone think a bad hub assembly or sensor would have waited this long to rear it's head again?