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.

It is known that these wireless switches being used to prevent muffler damper from closing causes problems with the wireless functions of the car.

Second is if you read the above closely you notice there is a lot more going to to the EFCM to simply be switching it totally off by turning off the voltage to the controller via these wireless switch functions.

Third as data shows the effects to fuel trims going lean when damper is open at low engine loads and as GM states above the concern for exhaust valve activity.

We suggest a better method that keeps the EFCM fully functional and could be done using a normal on/off switch ( or wireless could be used) by simply cutting the vacuum hose by the firewall as shown below and inserting a electric solenoid that is switched.

This way the EFCM is functional all the time and your simply controlling when there is vacuum to control dampers in mufflers.
We suggest as shown below a solenoid that has a coil that reacts very quickly and with low current draw.