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#4516646 - 09/14/17 11:17 PM Trailblazer ABS
Alex_V Offline


Registered: 04/10/16
Posts: 1155
Loc: Campbellsville, KY
2007 Chevy Trailblazer, 4.2L 2WD, with a very occasional occurrence of the ABS activating and pumping up the pedal under the driver's foot just before it comes to a stop.

Don't know how long it's been since the codes were cleared, but ABS history codes were:
C0455
C0244
U1000
U1016
U1064

No ABS light, only the tire pressure light that, at times, flashes even though all tires are generously aired.

Cleared all the codes and watched the wheel speed sensor data as I drove. Firstly, all WSS feeds except RR never read lower than 2; RR always reads zero, thought that was due to it being solid rear axle and only having one rear WSS which read as LR. As I'm driving nothing acts up, but the RF sensor reads down to 5 - very occasionally 4 - and drops straight to 2. Always does it, during decel and acceleration. Okay, says I, wheel speed sensor is bad and the ABS is kicking in because it thinks that wheel is locking up.

Replace sensor: no change in data, and now the ABS is kicking in on most stops. Saw the RR sensor data jump to a triple digit number for a split second as the ABS pumped up under my foot, then return back to its usual zero. And that's where I'm currently at.

Help?
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#4516663 - 09/14/17 11:52 PM Re: Trailblazer ABS [Re: Alex_V]
chemman Offline


Registered: 02/19/07
Posts: 70
Loc: Maryland
Not sure why you are chasing an ABS "problem" when the codes you provide are for a front steering position sensor circuit (C0455) and a PWM delivered torque malfunction (C0244). See http://www.tbssowners.com/forums/general-tbss-questions/186345-c0244-pwm-delivered-torque.html for more information on C0244.

The U1000 code is for a Class 2 communications error. The U1016 is a lost communication with the PCM/ECM error code, and U1064 is a lost communications with the Body Control Module.

Sounds like something other than an ABS problem.

Good luck!
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#4516666 - 09/15/17 12:00 AM Re: Trailblazer ABS [Re: Alex_V]
GMBoy Offline


Registered: 11/22/04
Posts: 7702
Loc: Texas
I did a quick scan thru the service manual and I see several mentions of bad EBCM or PCM. Of course, you need to follow the diagnostic tree to be for certain because it can also be steering wheel position sensor or simple bad connection somewhere such as the EBCM. I worry that because you have several U codes for loss of communication that you may be looking at a bad module either EBCM or PCM. Again - this is armchair diagnostics not being there to see the truck. My advice would be to unplug, clean, apply die-electric grease to every connection. This would include all wheel speed sensors, the PCM, EBCM, steering wheel pos sensor etc and check all grounds. From there, if it doesn't fix the issue, you need to do the detailed diagnostics but, again, you are having symptoms of a bad EBCM (I've seem that before) but I don't want you to throw parts at it - take time and root cause. If you cannot do this or lack a good scan tool and manuals then it is worth paying somebody who can.

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#4516824 - 09/15/17 08:19 AM Re: Trailblazer ABS [Re: Alex_V]
Alex_V Offline


Registered: 04/10/16
Posts: 1155
Loc: Campbellsville, KY
Anything very advanced with the actual electronics is a little above my pay grade and equipment level - I'm using a Snap-on "brick" to get what information I have. Engine electronics are more familiar to me, but ABS isn't something I've dealt with much. I'll clean connections and see what that does.
_________________________
I like Chevy and Valvoline.

'13 Cruze, 1.4T, 112K
'85 GMC C3500, 454, 130K
'82 Mercedes 300CD, OM617 turbo, 167K
'67 Suburban, 350, 331K

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#4521323 - 09/20/17 01:50 PM Re: Trailblazer ABS [Re: Alex_V]
Gasbuggy Offline


Registered: 08/26/09
Posts: 1895
Loc: PA
I think older GM ABS sucks big time and that sudden activation under normal braking can cause an accident. I've experienced it. I would pull the ABS relay, take the cluster out and break the ABS bulb. Fixed in 1 hour.
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#4531094 - 10/01/17 11:42 AM Re: Trailblazer ABS [Re: Alex_V]
tongboy Offline


Registered: 12/29/05
Posts: 2
Loc: Streamwood, IL
I have seen this happen before. Usually it's rust that forms between the hub/whatever and the sensor. It moves the sensor just a tiny bit away from the reluctor ring and causes the sensor to read 0 mph when you're still going a few miles an hour. It only happens at slow speeds.

I remember GM put out a tsb on this however I have seen it on all sorts of cars and trucks.

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