1997 GMC C2500 ABS light

Tiny
JOHN336
  • MEMBER
  • 1997 GMC C2500
  • V8
  • 2WD
  • AUTOMATIC
  • 87,000 MILES
My Abs light came on while driving tonight. The light came on, and I think the brakes were applied because the truck instantly started slowing down. Then after the brakes were touched slightly, the abs light turned off, and it was just fine. That happened twice. Then at one point the engine rpm's spiked, I am not sure if they were at all related, but it was strange.

Now the abs light is on all the time.

Ideas?

God bless,

John
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Friday, April 17th, 2009 AT 10:01 PM

6 Replies

Tiny
JAMES W.
  • MEMBER
John, this sounds a little strange. By any chance was it raining or did you drive through a deep puddle? If you had the cruise control set, a malfunction in the ABS will drop it out.
As a rule, you can have a complete failure of the ABS system and it won't affect your brakes. ABS is in addition to, not in place of, the brakes. What ever triggered the ABS light will be stored in computer memory. You need to have the ECM scanned and retrieve the code(s). This will help narrow it down. It's probably a bad wheel sensor. Hope this helps.
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Friday, April 17th, 2009 AT 10:14 PM
Tiny
JOHN336
  • MEMBER
James,

Thank you for your reply. Cruise was not on, and the roads were dry as a bone. I took the truck to Advanced Auto Parts this morning and they put a computer on it, and there were no codes. This morning too, the ABS light was not on. It is probably my abs sensor that is going out, so I will replace that. About the engine spike in RPM's I think that is hopefully unrelated. It was just amazingly strange timing.

This morning the truck died a couple of times while idling. If the engine was at higher RPM's no problem. I changed the fuel filter, and I think that fixed the problem.

Thanks for your help,

God bless,

John
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Saturday, April 18th, 2009 AT 12:40 PM
Tiny
JOHN336
  • MEMBER
I spoke too soon. Replacing the fuel filter didn't fix it.

God bless,

John
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Saturday, April 18th, 2009 AT 6:40 PM
Tiny
JAMES W.
  • MEMBER
I'm going to break this down. I think we have 2 different problems here and they're unrelated.
The stalling problem may well be a problem with the idle air control, IAC unit, on the intake/throttle body. It may just have to be removed and cleaned with carb cleaner.
I attached a diagram of your ABS system. I had to post it 1/2 at a time or it would be too small to read.
There are 3 speed sensors on the truck. One on each front wheel, and one on the output shaft of the trans. If any one of these 3 fails for just an instant, the ABS light will come on. 80% of the time it's one of these sensors that's scerwing up.
When you had the codes check at Autozone, did they check the brake section of the ECM, or just the performance section. The reason I ask is, whatever tripped the ABS light should be stored in ECM memory, but in a different section


http://www.2carpros.com/forum/automotive_pictures/248092_gmc_brakes_1.jpg



http://www.2carpros.com/forum/automotive_pictures/248092_gmc_brakes_1_1.jpg

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Saturday, April 18th, 2009 AT 8:57 PM
Tiny
JOHN336
  • MEMBER
James,

Thank you SO much! That is great.

I will go back to Auto Zone and make sure that they checked for all codes, not just on engine performance.

I will check the IAC.

I will try to leave you very positive feedback, but I last time it would let me leave any. It said something about not having enough points, or something.

Thanks again. This really helps!

God bless,

John
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Monday, April 27th, 2009 AT 2:51 PM
Tiny
TWARNOCK
  • MEMBER
John -

The SAME thing happened to my 1997 GMC 1500 V8 pickup. ABS light came on - truck seemed to slow down (almost like it wouldn't shift correctly.) It happens shortly after the truck is started and I start driving. It will correct if I stop, switch off the engine, and then turn it back on. Once (only once) did applying the brake solve the problem.

I have not checked the codes yet. However, I'd be very interested in hearing what resolves yours. I'll be happy to share what resolves mine if I figure it out before you!
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Thursday, May 20th, 2010 AT 6:14 AM

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