ABS unit Activating prematurely

Hi All,

I have a 99 GMC Sierra Z71 4X4, 5.3L, Auto, Short box

My ABS unit is activating prematurely, meaning when I depress the brake pedal, the ABS unit thinks I am really laying on the brakes and the unit should activate, I took it in to get it scanned, nothing abnormal came up on the computer for codes, the mechanic determined that the wheel sensors probably need cleaning (and\or) replacing

My question is...

Is this an expensive job? He told me that some trucks have the sensors built into the hub and if it can't be cleaned, the hub has to be replaced, he wasn't sure whether my truck was this type

Has anyone experienced this before? its going in next Tuesday to get fixed

PS, I already had replaced the whole ABS unit once on this truck in 2003, about 40K ago (very expensive)

Thanks in advance for your help (comments)

Brian

Reply to
99 GMC Z71
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Rust between the sensor and the hub. VERY common problem.

Yep, BTDT more than once.

its going in next Tuesday to get fixed

You can DIY if you have a few tools. All you need to do is pull the wheel/tire off. Then turn the wheel so the sensor is out some. Then go in with a wire brush and clean around it REAL well. Now you remove the bolt that retains the sensor, Then GENTLY stick a plug in the hole (make one out of a sharpie marker) Then clean off the rust and crud from the sensor and around the hole. Be GENTLE with the sensor, the wires are not that hard to break. Clean the tip off with some cleaner and once you have it all clean put a THIN coat of silicone grease on the Oring and slip it back in place. Tighten the retainer bolt down and then spray some paint around the sensor to seal it some. I also take an acid brush and coat around the sensor with some RTV. Keeps the water/dirt out to slow the rusting.

Reply to
Steve W.

I have the 'new' body style 2000 Silverado 5.3 4x4 LT EXT cab with 92K miles. I do like 99% of this Truck!!

I have had 4 front wheel brake sensors replaced.. 3 under warranty, 1 I paid.

There is a corrosion 'design prob' with these ABS front brake wheel sensors.

Wholesale sensor cost is about $65 ea... $120 retail each plus labor. I've learned by experience how brakes (1 or both) lock up early OR don't lock up at all at low speed. Bad in summer, real bad in Winter.

Dennis in WI

Reply to
Dennis Mayer

Update: If the Sensor can't be cleaned or sensor gets broken being removed.... Only the RH OR LH OR Both sensors get replaced.

The Axle hub only gets replaced IF the wheel bearings rust due to inadequate front wheel bearing greasing.

Every GM service person should know of the 1999-2000 common front brake sensor '$$ headache'. GM has a drive test box to understand which front brake wheel side is acting up.

Reply to
Dennis Mayer

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