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2004 gmc envoy_slt
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Discussion Starter · #1 ·
Hi all
Having a funky snag going on at low approx .5 to 1 mph speeds nearing a stop when brake pedal is modulated (pedal feathered) near the end of stop getting pedal pulses 2 or 3 "burps" and have no ABS light on and a while ago had light on but was traced to a open wire on the sensor harness r&r sensor and light went out and brakes good . Has anyone had this fault ??? and what could be a fix . would the dealer be able to t/s with scan tool simulate and find fault with no code ?
 

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2004 gmc envoy_slt
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Discussion Starter · #2 ·
sorry guys made a mistake the speed is more like 10 kmph or 5 mph when i get pedal pulse nearing full stop does the ABS system have a speed input other than the wheel speed sensor or does the ws sensor only sense a wheel lock up and not vehicle speed ?
 

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2003 gmc envoy_slt
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The wheel sensors check for differences in wheel speed, whether they are turning or stopped. IIRC, if one tire would be very low on pressure compared to the others, it could trigger a ABS action.
 

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2005 chevy trailblazer_ls
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I had this same exact problem!! Turns out it was a result of putting in new wheel bearings.
When I had my wheel bearings replaced and used the cheaper ones (big mistake):nono: . It is very common in GM's when the cheaper bearings are used (about $65 each):duh:. The ABS sensors are inside the actual bearing so they only way to fix it is to replace with good bearings (about $185 each).

If you haven't had the bearings replaced I would check with a mechanic.

Until I got mine fixed I pulled out the fuse for the ABS so it wouldn't keep going off (it was very annoying):hissy:. The ABS and brake lights will come on when you pull that fuse!
 

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2004 gmc envoy_slt
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Discussion Starter · #5 ·
still on the original front hubs but a while back had the abs light come on due to a broken wire on the drivers side r&r sensor (ac delco) and light went away and brakes were ok then like 2 weeks later light came on then went away on it's own could it be because the wheel speed sensors are miss matched in resistance due to one being old and one new ? think will get a new one for other side and keep old one as spare
 

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2004 gmc envoy_slt
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Discussion Starter · #6 ·
tire pressures are normal have 4 new tires and installed 2 new sensors thinking it could be a speed input problem does the abs have a speed sensor input or and input from the t case ans were are the rear wheel speed sensors i have a posi diff ??
 

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2002 chevy trailblazer_ltz
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Resurecting an old thread.

I'll be hooking the Tech 2 up today to see if that tells me anything. I developed this exact problem last night.

It seems to stop OK, but it is a bit unnerving when you're coming up to the back of a car at an intersection and the pedal is kicking back at you just before coming to a complete stop.

As a side note, on the drive home yesterday the Security light also came on in the dash. The problems didn't occur at the same exact time, but they did appear pretty close together.

Did the OP ever get a resolution to his problem?
 

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2004 gmc envoy_slt
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Discussion Starter · #8 ·
The op is still doing the same ol's_ _ _ gonna try the stepper motor next as for the abs now got a light on and i think it may be hub related but right now i'm in the middle of a ski-doo overhaul so it gonna wait for a bit
 

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Discussion Starter · #9 ·
oh and also found something funny with the snag with the abs i thought with the light on the abs/brake system reverts to basic braking ?? but mine still pulses in a lock up situation and the old fault of a " pre release " is gone ( i had no amber light on during pre release fault) i had pulled the fuse for a bit cuz was starting to bug me and a while back put fuse back in to see if it sorted it's self out but didn't and now i have a light man i wish i had a tech 2 scanner
 

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2003 chevy trailblazer_ltz
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Well in order to save you some trouble, may I say that as mentioned, do not purchase cheap replacements for wheel hubs. I am stilll fighting with these people and the last set I replaced was back in March! The bearings are good and make no noise but the speed sensors are crap. It may be time for hubs if they're OEM and have been in there for awhile.

One other thing I would suggest to you guys about pulling the fuse would be that if for some random reason you had another Brake system fault, you wouldn't know about it with the BRAKE light on and (if you have a DIC) SERVICE BRAKE SYSTEM message. I simply unplugged one of the sensors at the harness and sealed it off. ABS light on, but it stops fine and no other warning lamps. Seat belt light doesn't work for some reason with the ABS lamp on though. Maybe just another random fault with my truck.
 

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2004 chevy trailblazer_ls
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Mine pulses maybe once in a 45min drive but usually when im going over 30 or so and I tap the brakes and for a second the pedal pulses and the service engine soon light flashes on for a split second. Not sure WTF it is but I just live with it. I wish I could help but thought id say somthing so I can watch this thread......maybe give me some closure on my brakes?
 

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Well in order to save you some trouble, may I say that as mentioned, do not purchase cheap replacements for wheel hubs. I am stilll fighting with these people and the last set I replaced was back in March! The bearings are good and make no noise but the speed sensors are crap.
Good advice, that was exactly what my problem was.

My Tech 2 couldn't pull a code from the ABS system which seems to be somewhat a frequent problem according to the shop manual. But I was able to log the wheel speed sensor data and it turns out I had a bad speed sensor on the right front wheel in an aftermarket replacement hub.

I got them off of ebay but they were supposedly the, 'better' brand and OEM equivelent from what I've seen posted here I think. The hubs are fine, but after 15K miles the speed sensor went flaky.

The speed sensor was fine at speeds above 12 mph, but below that they instantaneously drop down to 3mph while the other front and single rear sensor slowly count down to 3mph. So the ABS system thinks during slow speed braking that the front wheel is locking up and kicking in the ABS.

I did save the original speed sensors when I replaced the hubs. It was a lucky thing I did since it was the problem.

Another problem with aftermarket hub is that the speed sensor is, 'almost' identical to the GM part but not exactly. The OEM speed sensor wouldn't seat all the way in the aftermarket hub. I took a micrometer to it and found the aftermarket part to be slightly smaller. I had to carefully ground down the OEM sensor to make it narrow enough to fit and seat properly. Luckily I was able to salvage the o-ring and reinstall it to seal the essembly afterward.

So another lesson learned from aftermarket parts, you ain't gonna find their supporting parts to be 100% compatible with the OEM. I usually do strictly OEM, but this time I took a chance because the supposed, 'quality' OEM part was half the price of going to the dealer for a pair. Had I not been able to modify the OEM part to fit I would have been stuck with a crappy replacement from the aftermarket manufacturer, if I didn't have to fight them for it as one poster here mentioned.

So OP, if you have a decent scan tool see if you can do any data monitoring and view the speed sensors while you brake. You might have the same exact problem I did.
 

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2002 chevy trailblazer_lt
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replaced wheel hub assembly

I have an '02-4WD-6cyl.-LT TB, bought with 35K miles in 2004, 2nd owner. Replaced the front left wheel hub assembly ($177.00) myself @ 78K miles. Haven't had any major problems really with the TB. Besides maintenance stuff, I've replaced the following items:

1. cam shaft actuator position solenoid
2. front left wheel hub assembly
3. windshield wiper motor
 

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2003 gmc envoy_slt_xl
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170 Posts
:tiphat Greetings to the crowd - Bought 2 hubs (TIMKEN GARBAGE) at Rockauto - paid the extra - 1st one I put in was a dud and the second one I now have the sensor problem - Thanks for all your notes. Tomorrow I pull the sensor off the old one and see if it will stop the ABS chatter at low speed.
Can somebody out there not make a quality product. LOL mine came in a Timen box - but the word was not stamped on it anywhere. I think they are just shuffling chinese junk like the rest. :duh::duh::duh: I had bought 2 to have one in stock ... no such luck...:crazy:
 
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