TCS/Stabilitrac activating unnecessarily - Chevy Bolt EV Forum
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post #1 of 5 (permalink) Old 05-14-2019, 11:49 AM Thread Starter
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TCS/Stabilitrac activating unnecessarily

I'm looking for some ideas on why this is happening, as my shop seems to be stumped.


2017 Premiere. It was in an accident last fall, and after waiting a *long* time for parts (LF wheel assembly) I got it back in March. Recently the TCS has been activating for brief periods when it shouldn't. It did it rarely a few months ago, but in the last few days, it's become quite common. On a 50 mile trip from home to the airport, there were 11 incidents. Each incident is from 1-5 closely spacex events where the TCS light on the dash flashes, and a varying amount of deceleration is applied to the car. Sometimes the effect is mild, and sometimes it's as strong as using the paddle on the wheel. It has a high frequency pulsing component, much like when ABS is engaged.


Conditions were dry. Speeds were anywhere from 55-70 mph. Most times, the car was maintaining speed, once it was under acceleration (a transition ramp from one freeway to another). Gradient was from flat to 5% downhill.


In *all* cases the car was on a sweeping right turn. Fairly significant lateral acceleration, but not enough to induce body roll.


Neither the shop nor I have found any OBDII codes to indicate a system malfunction.


I don't have a good sense for how the TCS wheel spin detection happens on this (or any other) car. I'm interested in suggestions.
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post #2 of 5 (permalink) Old 05-14-2019, 12:01 PM
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On a sweeping right turn, the left front wheel is making slightly more revs than the right front, so one might infer the TCS/ABS is being triggered at too low a threshold. Exactly how and why would be the question. First stop would be a thorough re-examination of all the left front brake and ABS sensor work and parts replaced after the accident.

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post #3 of 5 (permalink) Old 05-14-2019, 05:44 PM
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Probably a junk aftermarket wheel hub was used ???? If the hub wasn't replaced, it's probably damaged.
Most wheel hubs have a magnetic pickup and they get broken/cracked and will cause MPH dropouts.
If the bearing is damaged it can cause dropouts when the play allows the sensor gap to exceed it's limits.
This will usually happen when turning. The side load forces the gap to open.

Is the steering wheel centered properly ? An off center wheel can cause TCS system activation from
an unexpected high count deviation. The wheel has a sensor on the shaft and should read near/at Zero
with the wheel centered. Is "your shop" a dealer ? Most scan tools will not have the ability to see everything.

They may not see codes that could be there. I run into this a lot. Cheap scan tools won't work on new cars very well.
You'll miss at least half the information without GM's GDS2 system.
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Last edited by drdiesel1; 05-14-2019 at 06:44 PM.
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post #4 of 5 (permalink) Old 05-15-2019, 12:51 AM Thread Starter
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Quote:
Originally Posted by drdiesel1 View Post
Probably a junk aftermarket wheel hub was used ???? If the hub wasn't replaced, it's probably damaged.
Most wheel hubs have a magnetic pickup and they get broken/cracked and will cause MPH dropouts.
If the bearing is damaged it can cause dropouts when the play allows the sensor gap to exceed it's limits.
This will usually happen when turning. The side load forces the gap to open.

Is the steering wheel centered properly ? An off center wheel can cause TCS system activation from
an unexpected high count deviation. The wheel has a sensor on the shaft and should read near/at Zero
with the wheel centered. Is "your shop" a dealer ? Most scan tools will not have the ability to see everything.

They may not see codes that could be there. I run into this a lot. Cheap scan tools won't work on new cars very well.
You'll miss at least half the information without GM's GDS2 system.

The wheel is off by 3-5 degrees. When the repairs were done all new OEM parts were specified. Are there even aftermarket parts for Bolts? Seems a mite unlikely unless its shared with a higher volume vehicle.


The body shop outsourced the diagnosis (and alignment) to a Chevrolet dealership in the SF bay area, which has a fair number of Bolts. That doesn't guarantee competence, but it's better than an area that has none.
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post #5 of 5 (permalink) Old 05-15-2019, 12:23 PM
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Quote:
Originally Posted by martinknutson View Post
The wheel is off by 3-5 degrees. When the repairs were done all new OEM parts were specified. Are there even aftermarket parts for Bolts? Seems a mite unlikely unless its shared with a higher volume vehicle.


The body shop outsourced the diagnosis (and alignment) to a Chevrolet dealership in the SF bay area, which has a fair number of Bolts. That doesn't guarantee competence, but it's better than an area that has none.
If the wheel is off, this is most likely the cause of your issue. You're looking at the wheel and the TCM
is looking at the sensor input. The sensor is a much higher degree of measurement. The system has
a limited input threshold before it activates the system. The car has a YAW RATE sensor and a minor mismatch
between inputs will trigger your issue. The car is trying to correct itself.

Time to have the dealer or a competent alignment shop correct this issue.

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