What does it do and how does it work?
What do I look for as far as clutch, tire spin, brakes?
Thank you

 

Comp mode turns off Traction Control and increases the size of the dead band in the active handling algorithms in the Electronic Brake Control Module. The result is the driver can slide the car around more in a turn before active handling activates. It also causes the muffler valves to open at 3000 rpm instead of 3500 rpm.

If you don't know how active handling operates it basically works to reduce over or under steer in various situations. It uses inputs from the steering, yaw and lateral G sensors to calculate which front brake to apply to yaw the car in the direction the driver is turning the steering wheel. If the car is under steering it will drag the inside front brake and if it is over steering it will drag the outside front brake.

You can burn the rear tires off the car while in comp mode. The clutch isn't involved unless you use your foot to involve it.

From the GM FSM description of Active Handling:

Vehicle Stability Enhancement System (VSES)
The vehicle stability enhancement system (VSES) adds an additional level of vehicle control to the EBCM.

Yaw rate is the rate of rotation about the vehicle's vertical axis. The VSES is activated when the EBCM determines that the desired yaw rate does not match the actual yaw rate as measured by the yaw rate sensor.

The desired yaw rate is calculated from the following parameters:
• The position of the steering wheel
• The speed of the vehicle
• The lateral, or sideways acceleration of the vehicle

The difference between the desired yaw rate and the actual yaw rate is the yaw rate error, which is a measurement of oversteer or understeer. If the yaw rate error becomes too large, the EBCM attempts to correct the vehicle's yaw motion by applying differential braking to the appropriate wheel. The amount of differential braking applied to the left or right front wheel is based on both the yaw rate error and side slip rate error.

The VSES activations generally occur during aggressive driving, in turns or on bumpy roads without much use of the accelerator pedal. When braking during VSES activation, the pedal pulsations feel different than the ABS pedal pulsations. The brake pedal pulsates at a higher frequency during VSES activation.

Exhaust Tail Pipe Flow Control System Description and Operation
The Exhaust Flow Control (EFC) System enhances engine performance. The system has 2 modes of operation:

• Normal

• Competition

Normal Mode
When the vehicle is stationary with the engine running the exhaust flow control module (EFCM) commands the vacuum solenoid On, which supplies engine vacuum to both exhaust flow control valves. This causes the valves to close, diverting exhaust flow through a baffled path inside the mufflers. As vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3500 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open, diverting exhaust flow through an un-baffled path inside the mufflers, thus enhancing engine performance.

Competition Mode
When traction control is driver disabled, vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3000 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open; diverting exhaust flow through an un-baffled path inside the mufflers more frequently and at lower engine speeds.

The system also delays exhaust valve activity during wide-open throttle acceleration to inhibit exhaust valve actuation when the accelerator pedal is released and reapplied while shifting gears.

The EFCM has the ability to detect electrical malfunctions within the system. Any electrical malfunction detected will cause the system to be disabled and increased exhaust audibility.

The system uses the engine control module (ECM), body control module (BCM), electronic brake control module (EBCM), EFCM, exhaust flow control valve vacuum solenoid, vacuum reservoir, vacuum lines, 2 exhaust flow control valves and the serial data circuit to perform the system functions.

Bill

 

Excellent info from Bill about the system!!

Just to add a little bit more - there are 4 modes available by pushing the button on the console:

1. Default mode when you start the car is TC and AH full on
   
   
2. One push of the button - TC is off
   
   
3. Two quick pushes of the button - TC off, AH in Comp mode
   
   
4. A long push and hold of the button - TC off, AH completely off

I never turn anything off when driving on the street - absolutely no need to turn off stuff that might help if you hit a bunch of sand or gravel a truck dropped in the street, or a patch of oil that leaked out of somebody's junker.

I run Comp or AH completely off when running roadcourse track day events.

I don't drag race, but if I did I'd simply turn off TC - I'd leave AH full on to help keep me off the wall or out of the other lane if the rear end came loose.

Even with AH full on you can spin the car - AH can't overcome the laws of physics!! You can spin out in Comp mode too (hmmm....how do I know that??).

So...for street driving, everything is full on for me!

Bob

 

[QUOTE=Bill Dearborn;1583905496]Comp mode turns off Traction Control and increases the size of the dead band in the active handling algorithms in the Electronic Brake Control Module. The result is the driver can slide the car around more in a turn before active handling activates. It also causes the muffler valves to open at 3000 rpm instead of 3500 rpm.

If you don't know how active handling operates it basically works to reduce over or under steer in various situations. It uses inputs from the steering, yaw and lateral G sensors to calculate which front brake to apply to yaw the car in the direction the driver is turning the steering wheel. If the car is under steering it will drag the inside front brake and if it is over steering it will drag the outside front brake.

You can burn the rear tires off the car while in comp mode. The clutch isn't involved unless you use your foot to involve it.

From the GM FSM description of Active Handling:

Vehicle Stability Enhancement System (VSES)
The vehicle stability enhancement system (VSES) adds an additional level of vehicle control to the EBCM.

Yaw rate is the rate of rotation about the vehicle's vertical axis. The VSES is activated when the EBCM determines that the desired yaw rate does not match the actual yaw rate as measured by the yaw rate sensor.

The desired yaw rate is calculated from the following parameters:
• The position of the steering wheel
• The speed of the vehicle
• The lateral, or sideways acceleration of the vehicle

The difference between the desired yaw rate and the actual yaw rate is the yaw rate error, which is a measurement of oversteer or understeer. If the yaw rate error becomes too large, the EBCM attempts to correct the vehicle's yaw motion by applying differential braking to the appropriate wheel. The amount of differential braking applied to the left or right front wheel is based on both the yaw rate error and side slip rate error.

The VSES activations generally occur during aggressive driving, in turns or on bumpy roads without much use of the accelerator pedal. When braking during VSES activation, the pedal pulsations feel different than the ABS pedal pulsations. The brake pedal pulsates at a higher frequency during VSES activation.

Exhaust Tail Pipe Flow Control System Description and Operation
The Exhaust Flow Control (EFC) System enhances engine performance. The system has 2 modes of operation:

• Normal

• Competition

Normal Mode
When the vehicle is stationary with the engine running the exhaust flow control module (EFCM) commands the vacuum solenoid On, which supplies engine vacuum to both exhaust flow control valves. This causes the valves to close, diverting exhaust flow through a baffled path inside the mufflers. As vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3500 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open, diverting exhaust flow through an un-baffled path inside the mufflers, thus enhancing engine performance.

Competition Mode
When traction control is driver disabled, vehicle speed increases, throttle position reaches 25 percent or greater and engine speed reaches 3000 RPM, the EFCM commands the vacuum solenoid off. This causes the valves to open; diverting exhaust flow through an un-baffled path inside the mufflers more frequently and at lower engine speeds.

The system also delays exhaust valve activity during wide-open throttle acceleration to inhibit exhaust valve actuation when the accelerator pedal is released and reapplied while shifting gears.

The EFCM has the ability to detect electrical malfunctions within the system. Any electrical malfunction detected will cause the system to be disabled and increased exhaust audibility.

The system uses the engine control module (ECM), body control module (BCM), electronic brake control module (EBCM), EFCM, exhaust flow control valve vacuum solenoid, vacuum reservoir, vacuum lines, 2 exhaust flow control valves and the serial data circuit to perform the system functions.

Bill[/QUOTE

Thank You Bill,
Does the comp mode do anything to the clutch pedal as i noticed it was not popping back?

 

It doesn't do anything to the clutch pedal. Totally separate subsystem.

Bill

 

Steering feel changes with vehicle speed along with some other variables. From the GM FSM:

Variable Effort Steering System Description and Operation
The Variable Effort Steering (VES) system, or MAGNASTEER II® varies the amount of effort required to steer the vehicle as vehicle speed changes or lateral acceleration occurs. At low speeds, the system provides minimal steering effort for easy turning and parking maneuvers. At high speeds, the system provides firmer steering (road feel) and directional stability. When the system senses lateral acceleration, steering becomes firmer to reduce oversteering. The Electronic Brake Control Module (EBCM) controls a bi-directional magnetic rotary actuator located in the steering rack and pinion. The EBCM varies the steering assist by adjusting the current flow through the actuator. The actuator adjusts the amount of power steering assist to achieve a given level of effort to steer the vehicle. The VES system accomplishes this by adding or subtracting torque on the input shaft to the rack and pinion. The main component of the system is an electromagnetic actuator, which consists of a multiple-pole ring-style permanent magnet, a pole piece, and an electromagnetic coil assembly. The VES system uses the Antilock Brake System (ABS) wheel speed sensor inputs to determine vehicle speed. When the EBCM senses vehicle speed, it commands a current to the actuator that is most appropriate for each speed. The system also uses inputs such as Handwheel position, wheelbase, understeer coefficient and steering ratio to calculate lateral acceleration. The EBCM commands current from negative two amps to positive three amps to the actuator, which is polarized. At low speeds, a negative current is commanded, which assists steering. At medium speeds, no current is commanded and steering is assisted by hydraulics only. At high speeds, a positive current is commanded, which creates steering resistance. Ignition voltage and ground are provided through the EBCM. The EBCM has the ability to detect malfunctions in the actuator or the circuitry to the actuator. Any malfunctions detected will cause the system to ramp to zero amps and steering will be assisted by hydraulics only.


It doesn't specifically state that anything changes when using comp mode but you do see where the EBCM uses the same parameters used for the AH function in determining when to reduce/increase steering effort.

Bill

 

In comp mode i feel that my car is slower at the start and also throttle response is slower for some reason. is this normal? Its just at the start then later it is normal.

 

Does any of this apply to the A6 cars (VES, etc.)? I take it the A6 cars don't have a competition mode?

 

If AH isn't active it will not slow the car. When it is active it can slow the car when a brake is applied or it decides to request lower torque.

A6 cars have Comp Mode as well. To get Comp Mode push the button twice. One push turns off TC, the second push puts the car in Comp Mode and if you push and hold the button for a while AH and TC are both turned off.

Bill

 

Thanks Bill, that is the best explanation of the active handling, comp. & traction control modes I have seen to date. Certainly much better than the GM information in the owners manual.

 

Thank you Bill. I agree with jstewart. I haven't seen a more thorough explanation of things that I didn't even know existed!

 

I agree with all, this was the best explanation and now just have to find someplace to practice everything!
And buy a set of new tires when we are done!!
Thank you Bill

 

As in the pedal staying on the floor? Search for slave cylinder

 

Rtfm

 

Problem is they have to have the manual. This info isn't in the owners manual but is in the service manual.

Bill