If you have access to a tech II, You can monitor EACH sensor. The Three that you need to monitor are SWPS, Yaw and larteral accelorometer. Compare the readings in a LEFT turn and RIGHT turn. If the side that causes the brakes to apply are different, that sensor is most likely defective.

If a wheel speed sensor is putting out improper voltage or the wires/connectors are defective, it can also cause that issue.

What TCS DTCs are you seeing??

If I were you, I would pay very close attention to the SWPS output during the issue.

If the sensors are working correctly,,,,the EBTCM can and will cause that very same issue. The EBTCM is a costly part to replace so,,,,make sure that the other sensors are working correctly.

 

Thanks for that Bill,
I will give him this info and keep all informed on the results.

 

You should take the car to a large empty parking lot and do some testing. If you can find a place where you can drive quickly in about a 300 ft (100 meter diameter) circle drive the car at increasing speed until the front tires start to push. At that time AH should cut in and start hammering one of the brakes to get the car to yaw in the direction you are steering. Try turning in both directions. It is hard to tell from your descriptions of what is happening but I am wondering if the system is actually working the way it is supposed to work. The vast majority of Corvette owners have no idea what the system is supposed to do and are surprised that it does brake pulsing when correcting a yaw rate error.

Bill

 

Thanks for that Bill.
I will give this message to my mechanic.
I am driving the car to a Corvette show over this coming weekend (about 700 miles each way) so I will talk to the mechanic next week.
Thanks for your interest.

Regards,
George.

 

Hi All,
I have the car booked in with my mechanic next week and he will put the Tech 2 on it and see what he can find. The brakes are still grabbing when I turn into a street or driveway etc. so I checked the codes in the car and there is nothing showing up, so hopefully the Tech 2 will give us a better idea.
Will keep you posted.

George.

 

Hi All,
All evidence is pointing to the YAW sensor. The mechanic has tried adjusting or just moving or altering its position but no success. A point to note is that there are no codes showing up on the Tech II but the brakes are still grabbing when I turn into a corner or just do a U turn.
I can still drive the car but it would be good to sort out the problem.

 

Hi All,
Well its been a while but we are still working on this problem. After going through your suggestions, and what we had already done, we decided to buy a YAW sensor (apparently they can't be tested) and see if that fixed the problem. Well it sort of has. Apparently the sensor has to be dead level and dead straight ??? and even a few degrees out will make it play up. The mechanic has been trialling the position of the sensor and I took the car out last weekend and could only get the front wheel to grab once while going quite agressively through some corners. When it did grab it was only very slight and my passenger didn't even feel it. I knew what I was looking for, so I felt it. So, here is my next question.
I know what the idea of the Active Handling is, but when should it actually cut in? i.e. should it have actually cut in when it did or shouldn't it have done what it did? I have never driven the car agressively so am not sure when the AH should cut in.
Thanks in advance.

 

George

ANY,,, false sensor output can cause this issue. The sensors that you need to be looking at are:

-Wheel Speed Sensors (X4)
- Steering Wheel Position Sensor (SWPS)
- Accelerometer
- Yaw sensor.

Any sensor that reports an angular error signal OR slip / excessive wheel speed, will cause the EBTCM to modulate the brakes to keep the car on the drivers desired course (Steering Wheel Input) If the steering wheel sensor is reporting an error signal when your pointing STRAIGHT, the EBTCM/AH will respond with braking commands.

BC

The FIRST sensor that I would have suspected would have been the SWPS as it has the most reported issues. Sure YAW sensors go bad but,,, not all that often.

 

It actually sounds as if your active handling is working properly.

 

Have already replaced the SWPS and made no difference.

 

Mr's Curlee and Dearborn know far more about this system than I do and I'm getting in on this quite late in the hunt but I love a problem.

If I read it correctly, the original post mentioned the problem only occurs when cornering to the left. This brings to mind an asymmetrical event which may be the result of the SWPS thinking it is further left than center (or vice versa) when the steering wheel is dead center. Could this be a simple calibration issue?

 

Better late then never. I appreciate all the help and advice I am getting.
The problem actually is with any corner, left or right. I can get it to play up if I go into a corner (either side) at moderate speed. I may not necessarily brake before entering the corner. If I go slowly into the corner, everything is fine and no brake grabbing. I have already replaced the SWPS but I remember when the mechanic did it he stated that to set it you had to drive in a straight line for quite a few kilometres. I'm wondering as I write this if it is a possibility that it hasn't been calibrated correctly.
Also, after replacing the YAW sensor, the mechanic spent a lot of time trying to get the position of it right. Many times he would take the car for a test drive and it would behave itself for say 3 corners and then on the 4th one it would play up. He hasn't been able to find anywhere in the workshop manuals just how it should be positioned in the car.
Thanks for your interest guys.

George.

 

Since my earlier post I've learned the SWPS is self centering and would warn you if it were unable to. So it's unlikely that's the issue.



I've spent some more time looking at the Active Handling Option and discovered the system engages a caliper only when it senses "yaw rate error".

It turns out the EBTCM calculates yaw rate two different ways: "actual" using the yaw rate sensor, and "desired" using an indirect method involving the lateral accelerometer, the SWPS, and the wheel speed sensors at each wheel. The "yaw rate error" is the difference between the actual and desired rates.

If the actual yaw rate is less than desired yaw rate, the system identifies an "understeer" situation and pulses the inside front brake.

If however, actual yaw rate is greater than desired yaw rate the system identifies an "oversteer" situation and pulses the inside rear brake.

Since your car always seems to grab a front brake it is consistently identifying "understeer". Understeer happens when the outer front wheel starts to push, or slip slightly. You mentioned a U-turn could trigger your AH. A "brisk" U-turn is an understeer event.

This has already been suggested by Bill Dearborn in post #23 but I'll mention it again. Test the full range of the system. Drive the car to a very large empty parking lot where you can really test the active handling. Make the car understeer with a fast sweep making the front outer wheel push. Do left and right turns. The inner front wheel should grab as understeer develops. Then make the car oversteer left and right with a hard turn and aggressive acceleration. A wet rainy day is ideal! The inner rear wheel should grab if the system is working properly.

Also, try using the active handling system without the ABS/AT and see if there is any difference. By holding down the disengage button for 5 seconds you'll get a message saying "Competitive Driving Mode Engaged". It just means AH is on and ABS/AT is off.

If there is still a problem it's likely the car is confused from driving on the wrong side of the road. Try driving on the right for a while and see if the problem clears up.

Seriously George, do let us know how your tests go.

Crate.

 

Thanks for all this.
I have the car booked in next week so will print this out and give it to the mechanic. I am going to take the car to the people who convert them to right hand drive so am hopeful they will know about this problem.
Will keep you all posted.

George.