Slow speed abs activating problem


1go2alpha
11-22-2003, 03:13 PM
I have a 1997 GMC Sierra 4x4 with 5.7 engine. I am having the low speed coming to stop ABS activating problem. I checked the two front ABS sensor and they check out at about 1000 ohms each. I heard they should check out between 1000 -1400 ohms. Where is the rear ABS sensor located? I want to check that one also. Does this sound correct for diagnosis of ABS sensors? Any and all input is welcome.
Thanks, Rudy.

More Info. I put a voltmeter on the ABS sensor to get a reading.
The driver side show about .4 volts AC at 10 MPH while the passenger side showed about .8 volts at 10MPH.

99ssconv
11-23-2003, 04:09 PM
loose wheel bearing? improper air gap? the rear sensor is read from the vehicle speed sensor in the transfer case. the problem will be one of the front sensors or wiring. disconnect each sensor and set meter on ohms, probe the harness side (not sensor side) and wiggle test wiring, compare to other side, on a/c scale probing the sensor side spin the wheel by hand fast, improper air gap will show readings less than 350 mv. good luck

99ssconv
11-23-2003, 04:10 PM
Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)
1999-2000 Cadillac Escalade

1995-1999 Chevrolet Silverado (Old Style)

1995-2000 Chevrolet Suburban, Tahoe (Old Style)

1995-2003 Chevrolet Astro Van, Blazer, S10

1995-1999 GMC Sierra (Old Style)

1995-2000 GMC Yukon, Yukon XL (Old Style)

1995-2001 GMC Envoy, Jimmy

1995-2003 GMC Safari Van, Sonoma

1995-2001 Oldsmobile Bravada

This bulletin is being revised to change model information. Please discard Corporate Bulletin Number 02-05-25-006 (Section 05 -- Brakes).

Condition
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction
Measure AC voltage and clean wheel speed sensor mounting surfaces.

Raise the vehicle on a hoist.
Disconnect both the front wheel speed sensor harness connectors.
Place a DVM across the terminals of each sensor connector.
Rotate the wheel with hand speed and measure the ACmV's. The reading should be at least 350 ACmV's.
If the reading is between 200 and 350 ACmV's, remove the wheel, caliper and rotor in order to gain access to the speed sensor.
Remove the wheel speed sensor and plug the hole to prevent debris from falling into the hub during service.
Clean the speed sensor mounting surface on the hub to remove rust and corrosion.

Important
Make sure that the sensor sits flat on the hub. If the sensor flange is distorted, replace the sensor.


Apply a thin layer of bearing grease to the hub surface prior to sensor installation.
Install either the original sensor or a new one in the hub and secure the sensor. Ensure that the sensor is seated flush against the hub.
Install the rotor, the caliper and the wheel.
Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel by hand. The voltage should now read at least 350 ACmV's.
Warranty Information

KillaBug
05-12-2004, 11:37 AM
I have the same problem on my friends 95 Sierra Turbo/Dsl. I followed the guide given here and found the drivers side sensor to be opperating normally, while the passenger side gave off no voltage at all. Cleaned it all up good and still no voltage. Assuming a bad sensor I replaced it with a new one from the dealer to find still no voltage. The mounting surface has been cleaned well, and the sensor is brand new leaving me confused. Is it possible the reluctor ring needs to be changed? Although this does not make much sense to me, I'm really starting to fish for the solution.

GMCTech
05-12-2004, 05:58 PM
You will need a front wheel bearing or two. Your dealer knows WELL about this.

We do just about 4 a week.

Hope this helps.

1go2alpha
05-12-2004, 09:20 PM
You will need a front wheel bearing or two. Your dealer knows WELL about this.

We do just about 4 a week.

Hope this helps.

It has less than 43000 miles on it.
Thanks, Rudy.

KillaBug
05-13-2004, 04:36 PM
Thanks for the help, the dealer has been trying to sell me an entire hub assembly. Think I'll go to AutoZone and pick up some bearings and new racers. Thanks again.

GMCTech
05-13-2004, 05:41 PM
Unfortunately you have to replace the entire hub assembly.

AutoZone has an aftermarket version, but I would not suggest it. - You WILL be replacing it under a year (two at the most).

GM has redesigned the hub. I have yet to see one of the new designs fail (and we have done a 100 or more in the last 3 years)

Hope this helps.

1go2alpha
05-13-2004, 06:59 PM
Unfortunately you have to replace the entire hub assembly.

AutoZone has an aftermarket version, but I would not suggest it. - You WILL be replacing it under a year (two at the most).

GM has redesigned the hub. I have yet to see one of the new designs fail (and we have done a 100 or more in the last 3 years)

Hope this helps.

Does the 1997 have the one piece hub, ABS assemble or are they seperate?
Thanks, Rudy.

GMCTech
05-14-2004, 05:20 AM
The assembly is one piece hub and ABS - The only thing that is changable is the ABS wheel speed sensor, but that only gets changed if it is damaged.

p-ratt
05-14-2004, 05:08 PM
I am having the exact same problem.
Took the sensors out, cleaned and remounted them...problem still occurs.
How much (approximately) has it been costing to actually do the proper repairs on it?

GMCTech
05-14-2004, 09:08 PM
The hub assemblies are variable in price - most are around $300 there are a couple models that top $400 but I am unsure which models exactly.

You should be charged about one hour per bearing labor.


Hope this helps.

girouxs
12-15-2004, 08:44 PM
loose wheel bearing? improper air gap? the rear sensor is read from the vehicle speed sensor in the transfer case. the problem will be one of the front sensors or wiring. disconnect each sensor and set meter on ohms, probe the harness side (not sensor side) and wiggle test wiring, compare to other side, on a/c scale probing the sensor side spin the wheel by hand fast, improper air gap will show readings less than 350 mv. good luck

Do you have technical bulletin for Sierra 1999 new style? Is it possible that the problem is generate by rear sensors? Where are they?

Thank you for help.

gregborz
01-28-2005, 08:23 PM
Finally I have found someone else with the same deal. My brakes lock and the ABS sound kicks in at 8mph down to 4mph. The thing only has 24,000 miles on it and the dealer just replaced the sensors, but that didn't help at all.

Any ideas? My brakes are bad, but should that matter here? It is so weird that the low speed braking is messed up. It is a '02 and has such low miles...

emailj
03-22-2005, 08:58 PM
Finally I have found someone else with the same deal. My brakes lock and the ABS sound kicks in at 8mph down to 4mph. The thing only has 24,000 miles on it and the dealer just replaced the sensors, but that didn't help at all.

Any ideas? My brakes are bad, but should that matter here? It is so weird that the low speed braking is messed up. It is a '02 and has such low miles...

I actually got a recall from GM for the sensitive ABS system could cause a crash. The recall lists it as "FRONT WHEEL SPEED SENSOR CORROSION" This part will be checked, and possibly replaced if found to be corroted.

On another issue I also just received a recall on the Tailgate Support Cables

gregborz
03-22-2005, 10:20 PM
I actually got a recall from GM for the sensitive ABS system could cause a crash. The recall lists it as "FRONT WHEEL SPEED SENSOR CORROSION" This part will be checked, and possibly replaced if found to be corroted.

On another issue I also just received a recall on the Tailgate Support Cables

I received a tailgate recall a while back. Haven't gotten the front wheel speed sensor recall. The dealer here in Miami (Brickell) was awesome in taking care of my problem though.

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