Traction control...

Quick question, which sensor sends the wheel slippage data to the EBCM? Does the ABS sensor play a dual roll?

I have a 2002 Impala LS, and my issue is that the traction control will crap out after driving for a bit. It will send a warning "service traction control" and disable itself as well as the ABS. If I turn off the traction control manually before I start to drive, it will not fail, but it will also no turn off the ABS system as it would with a normal failure. I am trying to pin this down to a sensor issue or computer issue. My new ODB2 reader is coming in soon since the crappy one I had broke, so I figured I would get some info in the mean time...

I'm no expert but I do know that there are speed sensors in each front wheel hub that send information to the EBCM... I must have one sensor going bad because every once in a while the "Traction Control" light comes up on the dash for a few seconds... I'm told I will need to replace the front wheel hub assembly that has the bad sensor... The question is how do I determine which hub has the bad sensor...

Gems I think that is normal, when your wheel starts to slip , traction control is displayed , showing that it was just employed. ....unless your wheel is not slipping, like in snow, sand, wet....etc. Those wheel bearings i would imagine are expensive. I had to replace one on my Celebrity and from GM it was $250 and that did not have a sensor.
chevy2002 what scan tool did you get ?

I was just thinking, if you have the option where you have the warning that your tire is going flat. That uses the same sensor. Apparently as your tire goes flat, it turns slower. So i would think that if the sensor is going bad you would have false " flat tire " warnings. Unless for the flat tire it uses a larger time base for sensing to cancel out wheel slipage.

I don't mean to hijack this post... Let me just reply quickly... There was no wheel slippage when my trac control light went on... The 2 times it happened I was slowly pulling out from a parking spot on dry pavement... I was going 5MPH max...

My 01 has been doing it for 20,000 miles.I dont know which hub it is.But i read on this site that it has to be a front hub .I am not sure if that is true. I did change both my front hubs at 150k. I now have 178k.They tell me the dealer can scan it to see which hub it is.But i also dont know if that is true.

They tell me the dealer can scan it to see which hub it is. But i also dont know if that is true.

Thats correct. The GM dealer's Tech II will have no problems detecting flaky ABS sensors or properly reading ABS or traction control system DTC error codes. Also, scanners like the SnapOn MT2500 can do the same. The scanner must have the capability read GM ABS/Chassis codes.

Another thing you can do DIY is check is the electrical connector at the wheel sensor located in the hub. Look for corrosion or moisture, Also, with a multimeter measure across the wheel sensor terminals and look for a resistance value of around 1K ohms. Check all four wheels.

I have the Equus 3030, it should be in soon to replace the other one I had.

http://www.iequus.com/item.asp?cid=7&pid=3030

It can read manafactrer DTC codes as well....I will see what it tells me.

I figured it would be the hubs, I just replaced the front ones a few days ago. I am going to check the abs sensor connects when the weather clears up this weekend. Hopefully the scan tool is in this weekend too....

I have the Equus 3030, it should be in soon to replace the other one I had.

http://www.iequus.com/item.asp?cid=7&pid=3030

It can read manafactrer DTC codes as well....I will see what it tells me.

I figured it would be the hubs, I just replaced the front ones a few days ago. I am going to check the abs sensor connects when the weather clears up this weekend. Hopefully the scan tool is in this weekend too....

It looks like a good scanner for its intended purpose and cost. Very similar to my Actron CP9145. However, you may encounter problems reading GM ABS/Chassis codes with these type scanners and the translation may be incorrect. I did not see in the specs where it definitely was ABS capable.

GM ABS/Chassis codes for a typical "W" body car running a ABS VI or higher system starts at C1211 and end around C1363 not counting serial data codes.

For example a left wheel sensor that is flaky may show a DTC error code of C1225 (Left Front Excessive Wheel Sensor Variance) with the proper scanner.

My Actron as good as it is will not read that code out properly.

At the Equus web site there is a place to input a DTC error code. Type in C1225 and see what you get. It is not in the Equus database which is the same programmed into their scanners.

Hopefully it works but there is no guarantee it will accurately diagnose GM ABS and traction control problems.

Another thing you can do DIY is check is the electrical connector at the wheel sensor located in the hub. Look for corrosion or moisture, Also, with a multimeter measure across the wheel sensor terminals and look for a resistance value of around 1K ohms. Check all four wheels.

Thanks!! I will do that this weekend...

Thanks bnaylor.I did check all the connections already.Is it true that it has to be one of the FRONT bearings to get the (service trac lite). The reason i ask is because i already changed the front hubs. The rears have 178k miles.The fronts have 20k miles.

Thanks bnaylor.I did check all the connections already.Is it true that it has to be one of the FRONT bearings to get the (service trac lite). The reason i ask is because i already changed the front hubs. The rears have 178k miles.The fronts have 20k miles.

Front hub/bearings only? Not according to the GM service manual. Any one of the wheels sensors at any wheel can give you the service traction control and ABS lights. However, the front ones are the most likely suspects. Because of the FWD the front end gets more of a pounding or wear n tear than the rear. I've seen a rear wheel sensor cause it but that was a wiring problem. A tech while installing struts damaged the wiring going to the wheel sensor. What brands hubs did you use on the front end?

Thanks bnaylor.I did check all the connections already.Is it true that it has to be one of the FRONT bearings to get the (service trac lite). The reason i ask is because i already changed the front hubs. The rears have 178k miles.The fronts have 20k miles.
As Bob said a Snap on mt 2500 will give you abs codes, also they have a troublehooter cartridge for the abs to narrow the problem down. A std mt2500 will allow you to monitor wheel speed sensor inputs. Careful with the codes, I have seen this and other scanners read false codes. Focus on the speed sensor inputs first, correct that issue, clear the codes and see what happens.

I've seen a rear wheel sensor cause it but that was a wiring problem. A tech while installing struts damaged the wiring going to the wheel sensor. What brands hubs did you use on the front end?[/QUOTE]


I put in ones made in mexico.The first ones had noises after 10 miles.They replaced them.Then these seemed OK but i suspect that i should have put in GM hubs. These mexico ones are garanteed for a year but i hate to keep replacing them.And now im not even sure if its the front ones.

I put in ones made in mexico.The first ones had noises after 10 miles.They replaced them.Then these seemed OK but i suspect that i should have put in GM hubs. These mexico ones are garanteed for a year but i hate to keep replacing them.And now im not even sure if its the front ones.

The only hubs I've used or trusted are the GM/AC Delco, BCA-Federal Mogul or Timken brands.

As suggested the best thing to do is run it on an ABS capable scanner to see which wheel sensor is flaky or at least narrow it down.

I had the whole enchilada of issues with the traction contol system on my 01 Impala LS, 105,000 mi, starting with the warning lights, hearing the ABS come on from a stop for no apparent reason (i.e., good traction on clear pavement), traction system going into disable mode etc.. When it first started (around 95K), the dealer did not find any codes. I checked the ohms at each sensor and came up with the 1K ohms bnaylor recomlmended looking for, but still problems. After going back to the dealer at 105, they did find a code for bad ABS sensor in the right front. I ended up doing the job for less than 1/2 of the dealer price. I used BCA hub/bearing assy which is made by Federal Mogul vs the OE by AC Delco (also about 1/2 the price). Problem is completely gone, as well as a quieter ride (I guess the bearings were going too). Hopefully the BCA product holds up.

After less than 5000 miles, the problem with the ABS light is back after replacing both fronts with with BCA hub bearings. Dealer scan shows right from throwing the code. Not looking good for BCA bearings. A new one has been ordered. Will post update once thats in an some miles have been covered.

2 factors to consider before blaming the hub bearings.

1. Was the new bearing installed with an impact wrench?
2. Was the axle nut torqued to the proper spec provided in the box?

ABS sensor equipped hubs are fragile, and cannot be installed with impact tools, especially the axle nut. The hammering action either cracks teh abs sensor, or imparts microscopic dents in the bearing race causing high frequency vibrations that destroys the ABS sensor. Many aftermarket hubs require a different torque spec than the factory bearings due to changes in design. Failure to follow the torque spec supplied with the hub (when different from the OEM spec) will cause premature failure of the hub bearing.

Guilty on all counts, your honor. Thanks for the heads up - I'll be adjusting my tactic for the replacement bearing. Thanks again.

BCA replacement is in, and hub nut put on without air gun. No torque spec with new bearing, so 159 ft lbs was used per the number in the Haynes aftermarket manual. Anyone with factory spec knowledge know if this is correct? After two weeks (about 1000 miles), the trac lite, service traction control lite, and track off lite are all on. I am at wits end. For what seems like a simple replacement, this is becoming a nightmare. Haven't had the codes read yet. I notice that the wheel hub nut is warm on the front right (bearing that was replaced) vs left front (also replaced in Nov 06) which is barely warm to touch. I'm wondering if problem is due to bearing quality (not OEM) or if some other issue is causing the problem. Any suggestions greatly appreciated.

You need to get it scanned to be sure the bearing is the issue. You can grab a digital multimeter and ohm check the connector coming out of the hub, it should read around 1k ohms.

I am having the same problem with my 2002 Impala for the last six months. The dealer said it gave a generic code which meant either it had a bad wheel sensor or a bad modulator for the entire system (cost of that part $1000). They could not fix it until it gave a good code that would tell them what was wrong. It worked okay for about a month. Next time I tried a national brake shop. They drove my car which was getting the error message and the brake would pump into the driver's foot when being applied plus the car made "RRRR" noises. They got an excessive wheel spin on the left wheel and replaced the hub. 500 miles later and it was back but worse. The brake shop said there was no code this time but thought perhaps it was thin, warped rotors. Front brake job even though the pads were only 60% worn. The back brakes are in great shape. Car has less than 53,000 miles. One week later the "Service Traction System" and ABS lights were back along with the noises. Had the tires rotated. The car was fine for a couple of days and then the problems were back again. Two people have suggested a bad computer chip but the computer was replaced sometime in the last 16,000 miles. Any additional suggestions?

Mine went away. I have a power tunner by hp tuners. The last time I uploaded my changes to the cars OS I selected re-link VATS. I think that re-establishes the link with the other onboard computers. Anway now when i accelerate no trac off and have traction unit serviced.

Inquire as to what company manufactured the wheel bearing that was installed if you don't already know. Anything produced by the Federal Mogul group will likely cause problems. They sell under names such as National or BCA. There are also other aftermarket NOS that would also be in the avoid category. If anything other than Timken or AC Delco was used, my suggestion would be to replace the bearing again with either of those names (the Timkens can be found for less $$ than the AC Delco, but they can still be 2x the cheap brands - money well spent!). I went through a period of several months putting up with the problem you describe (see my earlier posts). I tried the Federal Mogul made bearings twice - complete junk as far as I'm concerned. Each time the problem would be back in under 5,000 miles. The quality issue has been stated on this forum by those more experienced than me. If Timken or AC Delco were used, then the wiring harness to the sensor could be an issue. This solved the problem for someone from another message board. I found out from my local repair shop that he chased down a wiring issue on a 2001 Impala that was causing the ABS light/Traction light combo to come on. Good luck on getting it fixed.

Thanks for the posts. I'm going to take my car, along with all the responses and searches, to a very good local mechanic and have him check the wiring harness. The wiring sounds like it is the most likely culprit. What a relief to finally have a clue as to the possible problem. Will respond back by the end of the month if that finally fixes it or not.

Finally got my car fixed last Friday.by a great but extremely busy local mechanic. He knew immediately the solution to my problem when I told him over the phone the make of the car and that the Service Traction Contol message and ABS light kept coming on. He said he had another Impala coming in that day with the same problem to be repaired. He has repaired several Impalas with this problem. He said it took him a while to figure out the problem on the first Impala he saw with the Traction Control/ABS problems. He is surprised Chevy isn’t doing a recall because he thinks it could be classified as a safety issue. Anyway, he said that the problem usually occurs on the driver’ side of the car. It is the wiring harness which is too short considering all the stuff that is on that side of the car. The replacement harness is longer (it looked like he indicated about a foot or so longer). The replacement wiring harness runs about $50. It cost me a total of $109 to get it fixed including labor, supplies, part, and tax. He also cleared the codes. When I got in to drive it, the pedal felt like I had hardly any brakes. The ABS system must have really been messing the pedal and I got used to a heavy feeling. It feels normal now and drives great! He did check out my car and the National Brake Chain did everything they said they did. Since I have a new left wheel hub, brand new front rotors and brake pads, this mechanic said my car is set for a long time. The problem is he is so good you have to make an appointment way in advance or leave your car for several days before he can get to it. He can not only repair normal things but he can track down wiring problems.

Bottom line – get the wiring harness replaced on the left driver’s side of the Impala.

I have an '02 impala and am having the same problems with the ABS and traction control. I Just replaced the hub bearing on the drivers side due to a slight wobble. Still have the ABS problem. What I noticed about the connector from the hub to the wiring harness was a little play. I took some electrical tape and taped the connector so it was tight and did not bend and I've been driving for 3 days now with not a peep from the ABS. the wiring harness itself looks to be in good shape.