The dealer recently replaced the body control module in my car after it had a problem with it.

Prior to this, I always noticed that whenever a wheel would slip and the traction control would kick in, that it felt like the electronic throttle was cut off, and the car would hesitate, quite dramatically, whenever the traction control engaged.

Since the new body control module was installed, I no longer get the hesitation feel when the traction control kicks in, and I can actually make the wheels slide a bit under heavy acceleration and it feels like it is just on the edge of traction, and I can actually make the rear end squirm around some searching on the edge of traction now, with the rear tires spinning just enough to make some noise. For a while I almost thought the traction control wasn't working, so I shut it off just to see the difference, which allowed me to totally light up the tires. So it does seem to be working, only differently than it did before. It seems like maybe the programming that controls it has been changed, and I'm wondering if maybe the new Body Control Module I got has new firmware programed into it.

So I guess I'm wondering, what does everyone elses car do when the traction control kicks in? Is it a an intrusive experience and you feel a hesitation like you completely lifted off the gas pedal, or do you not even really notice it?

My car is a 2008 just for reference. My suspicion is that the system has been improved some in recent years, and maybe getting a new body control module installed upgraded the way the system works. Can anyone confirm or deny this theory?

 

There has been some minor tweaking over the years, but I don't think anything that would produce the difference you got with your new BCM.

What you describe before replacement sounds more like what happens when you don't have any tire pressure sensors installed, or if they aren't properly programmed into the TPMS computer in the car.

Did they do anything to tire pressure sensors or TPMS while doing the BCM swap???

If there are no tire pressure sensors, or if they sense low pressure in any of the tires, the TPMS sends that info to the BCM and ECM, and the TC and AH systems are VERY intrusive and will pull power like you describe in your "before" experience - the so-called "limp mode".

If you weren't having any tire pressure sensor/TPMS problems, then your old BCM may have had some corrupted files in it, and the new BCM has the proper programming to operate everything like it's supposed to work.

There are very few people that have any idea about the software programming in many of the modules in the car - GM keeps that stuff secret better than the gubmint maintains our national security secrets!!

Forum member GTPprix is the only person I know of outside of GM that can probably answer about differences through the years, but I'm pretty sure there's nothing really significant.

I don't think you're seeing big differences due to the difference in software programming throughout the years, but mainly because your old BCM had problems that required its replacement.

Bob

 

Thanks for the feedback. Maybe I was in "limp mode" all along and didn't even know it.

So how is the car supposed to react normally when the traction control engages? Is it supposed to totally shut down all wheelspin, or just reduce it? I'm still able to get some wheelspin even with the traction control engaged, but it greatly reduces it.

I'm also running Michelin A/S tires that aren't as sticky as the OEM tires, so maybe it can't pull enough power to totally stop wheel spin. From reading the service manual, it also appears that it applies some brake as well when it engages.

 

Actually the EBCM (Electronic Brake Control Module) is what controls the Traction Control System.

The BCM mainly sends messages about the system to the DIC.

There are 2 different things (actually 3, if you have PTM, and maybe 4 if you take into account that AH also will try to reduce loss of traction from skidding type situations) that will limit power to the rear wheels:
Traction management is programmed into the ECM/PCM (Engine Control Module/Power Control Module, whatever you want to call it) to limit power to reduce the potential for damage to the driveline/power train components. Engine tuning programs (HPTuners, EFILive, etc.) can be used to tune it out - well, not really tune it out, but raise the point of its intervention so that it's not really a factor anymore.

The TCS is mainly controlled by the EBCM, and when rear wheel slip occurs during acceleration the EBCM first sends a message to the ECM to reduce power by reducing timing, and if that doesn't work, by reducing fuel flow by shutting off injectors.

If the engine torque reduction doesn't stop wheel spin, the EBCM will take control and apply the rear brakes.

During all of this the EBCM sends a request to the BCM to display the message "Traction System Active".

Of course you can turn off TC with the button on the console, but you can't turn off Traction Management unless you have a tuning program.

So.....I think the TCS tries to reduce wheel spin, not necessarily completely stop it.

I'm still wondering if you were having any indications of tire pressure sensor problems, or if you were getting anything like a "Service Tire Monitor" message.

If you have sensor or TPMS problems the TC and AH systems are VERY intrusive, and that's mainly what will invoke the "limp mode" and cause really noticeable reductions of power and applications of brakes.

Bottom line - I don't think replacement of your BCM has much to do with a change in the way your TC is working.

Bob

 

I can relay my controlled experiences at auto-x's in this regard. Picture going full throttle right at an apex in second gear.
With the TCS on ; beginng tire spin feels full power for 10 ft.,then does feel deminished for about the next 20 ft. , then complete traction almost like a bog, or just high engine load. I can't tell if it is from reduced power or the brakes were activated . So TCS takes 20-30 ft. to
bring the car under control.
Same test TCS off - tire spin the same through 10 ft. ,then more power starts spinning the tires more violent for another 30-40 ft. almost into the third gear shift point.
Quite a difference, and I have always felt the TCS was too slow in my car for street application.

 

The traction control for the C6's is a lot less intrusive then it was on the C5's.

With my 2009 Z06, it will easily spin the tires, but the traction control doesn't shut down the power as it did in the C5, but limits the amount of tire spin. On some days it really feels as if the car is down on power, but what is happening is that the rear tires are spining and since the car isn't pulling as hard it feels as it the car is down on power. I do realize that the computer has cut some power to minimize the amount of tire spin.

 

I never had any problems with any of my tire pressure sensors, and all four of them give me good readings.

A couple times after I first bought the car I got the "Active Handling System Error" message in the DIC for a second or two, but then it went away, and it never came back. I did read alot about the bad connector under the dash, but since the error only happened a couple times, and then immediately went away, I never thought much more about it.

I guess I must have been driving with the traction control system in the limp mode for the past 2 or 3 years and didn't even know it, because I just thought that was the way all of them acted. When the wheel would spin, it felt like someone just reached down and shut off the engine for about 3 seconds, and the throttle had no control of the car at all. It would just coast for a while until the system reset itself, and it was extremely intrusive. The BCM was replaced for a totally unrelated problem, and maybe they cleared a DTC when installing and programming it that fixed the Traction Control system, but I never got any error messages about the Traction Control system on the DIC, so I assumed it was working properly.