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2004 chevy trailblazer_ls
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2 Posts
Discussion Starter #1
My ABS is kicking in at low speed stops and I've been going over some forums and found that alot of people have had this problem after doing maintenance to the hubs or they had bad hubs I have neither. What I do have is a leaking rack and pinion fluid coming out of the boot, could a build up of fluid on the sensor cause this problem? Thanks
 

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2004 gmc envoy_slt
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2,503 Posts
ABS kicking in at low speed is usually always a bad hub, marginal speed sensor or a build up of rust and corrosion under the sensor mounting. In my case it was the rust build up. This is the easiest and cheapest thing to check out first.
 

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2002 chevy trailblazer_lt_ext
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4 Posts
I have an 02 trailblazer ext that we bought at a good deal knowing it had abs/brake problems. We bit off more than we can chew, I fear. We upgraded the hubs (due to high failure rates on replacing the standard OEM ones) and installed new rotors, etc. We get low speed abs activation when breaking (speedometer doesn't read at all when under 15 or 20 mph). Codes that showed up the first time and continue to show up are C0236, C0237 and C0269.

There was water in the brake fluid so we did a complete flush and there was hardly any pressure in the rear so we replaced the master cylinder.

Still getting low speed ABS activation, no speedometer at low speed, but when driving over 15 mph the abs light will go off (presumably because it can capture the rear wheel speed at that time).

We have replaced 3 or 4 speed sensors on transfer case. There was a loose connection at the VSS harness so we replaced that and now have constant continuity.

I'm at a loss on why the vehicle speed is not being registered. Grounds checked, etc.

My understanding is that in the 4x4 EXT model, the VSS captures the rear wheel speed signal for both wheels and reports it to the PCM. The PCM sends the pulses to the EBCM and the PCM also sends the signal to the speedometer cable.

I have poured hours into the wiring diagrams. We have swapped sensors just in case something odd was going on with the sensors themselves.

Any idea on what to look at next? There has to be something we overlooked.
 

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2002 olds bravada
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26 Posts
There is a TSB about rust under the wheel sensors. This is a problem with a lot of gm light trucks. Remove sensors, clean area down to metal. Use cold galvanized primer, wait until dry put sensors back in problem solved. Problem was so bad on my Silverado that I could not stop the vehicle at slow speeds because ABS kept pulsing. This is for 4wd front axle and 2wd trucks that have removable sensors from front hubs.
 
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