Found out something interesting - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 12-15-2006, 02:47 PM   #1
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Default Found out something interesting

Ok, I have been diagnosing why my traction control light on the dash stays on. Since I do not have any scantools that will diagnose that issue, I decided to run some tests of sorts. Here is what I found out:

1st test: Start car from cold condition, let idle, in park, 20 mins. run time. Zero light.

2nd test: Start car from cold condition, let idle in drive 20 mins, park brake set. Zero light.

3rd test: Start car from cold condition, high idle in drive for 10 mins, park brake set. Zero light.

4th test. Start car from cold condition, immediately go into drive and drive around...light.

So this ISN't temp. related afterall...hmmm.....and NO ABS light is on either...not a wheel speed sensor issue either.

5th test. Start car from cold condition, immediately go into 1st and set car in motion...drive to about 25-30 mph....zero light.

6th test. Continuation from 5th test in that I shift to "2"...observe slippage...light comes on.

It seems like Traction Control computer can actually diagnose slippage occuring. Anyone else know about this? BTW, ECM says there are ZERO codes now Looks like ECM is very happy with the FrankenMotor
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Old 12-16-2006, 11:21 AM   #2
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Yeah, The pcm has a variable for TCC Slip.
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Old 12-16-2006, 01:02 PM   #3
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Quote:
Originally Posted by sandrock
3rd test: Start car from cold condition, high idle in drive for 10 mins, park brake set. Zero light.
Thats hard on the transmission and torque converter.

The EBTCM (electrinic brake traction control module) does have the ability to detect wheel speed slip, this is what allows it to fuction. If it is setting the light only after the car travels above 3 mph, it is probably due to a faulty wheel speed sensor or its related wirring.
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Old 12-16-2006, 02:14 PM   #4
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Quote:
Originally Posted by 1fatcat
Quote:
Originally Posted by sandrock
3rd test: Start car from cold condition, high idle in drive for 10 mins, park brake set. Zero light.
Thats hard on the transmission and torque converter.

The EBTCM (electrinic brake traction control module) does have the ability to detect wheel speed slip, this is what allows it to fuction. If it is setting the light only after the car travels above 3 mph, it is probably due to a faulty wheel speed sensor or its related wirring.
But if it were a WSS, ABS light would also come on. Also on the 5th test, I drove around 20 mph with it ONLY in first gear, no upshifts allowed, and no traction off light. WSS'* are good. Though some of these tests are indeed hard on a tranny, I know for certain I have to either rebuild/replace mine no matter what. I was trying to determine whether or not TCS stuff was also on the fritz, not the strength of an already dead trans.

I always thought that the PCM and EBTCM were in no way, shape, or form connected to each other. If they are NOT connected, wouldn't this mean that the EBTCM senses trans slip and not the PCM?
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Old 12-16-2006, 03:29 PM   #5
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I think they might be connected, Let me look.
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Old 12-16-2006, 03:36 PM   #6
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Yup, CKT 800, Tan, 8A-50-0. DLC to HVAC, PCM, RAC, DERM, and EBTCM.
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Old 12-16-2006, 05:42 PM   #7
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Quote:
Originally Posted by Damemorder
Yup, CKT 800, Tan, 8A-50-0. DLC to HVAC, PCM, RAC, DERM, and EBTCM.
Hmm...very interesting. Thanks a bunch! Now, I didn't catch this in the FSM'*, but it seems as if once the ECM detects slippage, it turns off the traction control, but why?

Time to look at the books tomorrow and see if I can come up with an answer if someone else doesn't beat me to it
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Old 12-16-2006, 06:01 PM   #8
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What was your "high idle" ?
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Old 12-16-2006, 06:22 PM   #9
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Quote:
Originally Posted by Cheetah
What was your "high idle" ?
About a grand...just enough to build some heat up in there
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Old 12-16-2006, 07:11 PM   #10
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OK, I think I'm following now. Your transmission slips? This is turning off the traction control? It may be doing this to help prevent more damage to the transmission?

I think that when you have the shifter in manual low, it disables the traction control. This is probably normal. It'* just a default in the control module that bypasses the system. Letí* face it, if you put the shifter in manual low you did it for a reason and that reason is not to be interrupted by traction control. GM did this on purpose I'm guessing.

That tan wire, circuit 800, is the communication circuit that all modules use to communicate with each other and the ALDL. So yes, it looks like the EBTCM and PCM do talk to one another.
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