GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Corvette 🢒 Engine 🢒 Engine Exhaust 🢒 Exhaust Tail Pipe Flow Valve Mechanical System Diagnosis

Diagnostic Aids

System diagnosis includes reviewing the system Exhaust Tail Pipe Flow Control System Description and Operation . Reviewing the information will help determine when a malfunction exists. It will also help to determine if the condition described by the customer is a normal system operation. Refer to Symptoms - Engine Exhaust in order to identify the correct procedure for diagnosing the system.

A Scan Tool can be used to command the vacuum solenoid On or Off.

    • Vacuum solenoid commanded OFF
       - Engine vacuum is blocked to the exhaust flow control valves mechanically by the position of the solenoid valve.
       - Exhaust flow control valve vacuum diagrams are vented to the atmosphere mechanically due to the position of the solenoid valve.
       - Exhaust flow control valves are OPEN.
       - Exhaust gases flow through the least restrictive passage in the mufflers.
       - Exhaust gases exit all muffler tail pipes.
    • Vacuum solenoid commanded ON
       - Engine vacuum is sent to the exhaust flow control valve.
       - Both exhaust flow control valves CLOSE.
       - Exhaust gases must flow through a more restrictive passage within the mufflers.
       - Exhaust gases exit only the outboard tail pipe of each muffler.

Step

Action

Values

Yes

No

Schematic Reference: Exhaust Tail Pipe Flow Control Vacuum System

1

Did you perform the Diagnostic Starting Point - Exhaust Flow Control System?

--

Go to Step 2

Go to Diagnostic Starting Point - Exhaust Flow Control System

2

    Important: Engine is NOT running.

  1. Looking into the inboard tail pipes, verify that the exhaust flow control valves are both in the OPEN position.

    2. Caution: Refer to Exhaust Service Caution in the Preface section.

  2. Manually rotate the each valve to the closed position.
  3. Release the valves and allow spring tension to return the valves to the OPEN position.

Do both valves rotate CLOSED smoothly, without binding, and then return to the OPEN position when manual force is removed?

--

Go to Step 3

Go to Step 28

3
  1. Start the engine and allow it to idle.
  2. Verify that both exhaust flow control valves rotate to the fully CLOSED position.

Did both valves close?

--

Go to Step 4

Go to Step 6

4

Use a scan tool to command the exhaust flow control solenoid OFF.

Do both exhaust flow control valves Open?

--

Go to Step 5

Go to Step 21

5
  1. Use a scan tool to command the exhaust flow control solenoid ON.
  2. View both exhaust flow control valves from the rear of the vehicle.
  3. Have an assistant depress the accelerator pedal to the floor and immediately release the pedal.

Did the exhaust flow control valves remain fully CLOSED?

--

Go to Step 36

Go to Step 24

6
  1. Disconnect the quick connect between the vacuum check valve and the front chassis vacuum pipe, located near the brake booster.

    2. Important: If the O-ring is damaged, the exhaust tail pipe flow control vacuum check valve and hose will need to be replaced. Refer to Exhaust Tail Pipe Flow Control Vacuum Check Valve and Hose Replacement .

  2. Inspect the quick connect O-ring .
  3. Using a vacuum gage at the vacuum check valve, measure and record the vacuum signal at engine Idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 7

Go to Step 14

7

With the engine running, clamp off the rubber vacuum hose forward of the vacuum check valve.

Does the vacuum gage read steady within the specified range for 30 seconds?

16-30 in Hg (54-102 kPa)

Go to Step 8

Go to Step 29

8
  1. Remove the clamp from the vacuum hose.

    2. Important: If the O-ring is damaged, the line reservoir tank to control valve solenoid pipe will need to be replaced. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Reservoir Tank to Valve Solenoid .

  2. Disconnect the chassis rear vacuum pipe from the reservoir tank to valve solenoid pipe quick connect . Located under the vehicle at the from edge of the rear bumper.
  3. Using a vacuum gage at the chassis rear vacuum pipe, measure and record the vacuum signal at engine idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 9

Go to Step 15

9
  1. Connect chassis rear vacuum pipe from the reservoir tank to valve solenoid pipe quick connect .

    2. Important: If the O-ring is damaged, the line reservoir tank to control valve solenoid pipe will need to be replaced. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Reservoir Tank to Valve Solenoid

  2. Disconnect the vacuum pipe from the vacuum tank.
  3. Using a vacuum gage at the pipe, measure and record the vacuum signal at engine Idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 10

Go to Step 17

10
  1. Disconnect the vacuum pipe from the left flow control valve.
  2. Using a vacuum gage at the pipe, measure and record the vacuum signal at engine Idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 11

Go to Step 18

11

Using a J 35555 Metal Mityvac at the left flow control valve, apply at least 16 in Hg (54 kPa).

Does the left flow control valve close?

--

Go to Step 12

Go to Step 28

12
  1. Disconnect the vacuum pipe from the right flow control valve.
  2. Using a vacuum gage at the pipe, measure and record the vacuum signal at engine Idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 13

Go to Step 33

13

Using a J 35555 at the right flow control valve, apply at least 16 in Hg (54 kPa).

Does the right flow control valve close?

--

Go to DTC P166A

Go to Step 28

14
  1. Connect the vacuum check valve and the front chassis vacuum pipe.
  2. Disconnect the vacuum hose at the vacuum check valve.
  3. Using a vacuum gage at the vacuum hose , measure and record the vacuum signal at engine Idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 29

Go to Step 19

15
  1. Connect the vacuum hose to the vacuum check valve.

    2. Important: If the O-ring is damaged, the rear chassis vacuum pipe will need to be replaced. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Chassis Rear .

  2. Disconnect the rear chassis pipe from the reservoir tank to valve solenoid pipe, located left of the transmission.
  3. With the engine running, use a vacuum gage at the front chassis pipe, measure and record the vacuum signal at engine Idle.

Does the vacuum gage read steady within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 16

Go to Step 30

16
  1. Connect the pipes.

    2. Important: If the O-ring is damaged, the rear chassis vacuum pipe will need to be replaced. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Chassis Rear .

  2. Disconnect the quick connect in the rear chassis vacuum pipe, located above the transmission.
  3. Using a vacuum gage at the forward part of the rear chassis vacuum pipe, measure and record the vacuum signal at engine Idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 31

Go to Step 36

17
  1. Connect the quick connect.
  2. Disconnect the vacuum reservoir tank to valve solenoid from the vacuum valve solenoid.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 34

Go to Step 32

18
  1. Disconnect the chassis rear vacuum pipe from the reservoir tank to valve solenoid pipe quick connect . Located under the vehicle at the from edge of the rear bumper.
  2. Disconnect the reservoir tank to valve solenoid pipe from the vacuum solenoid.
  3. Using a J 35555 apply at least 16 in Hg to reservoir tank to valve solenoid pipe.

Can 16 in Hg of vacuum be achieved?

--

Go to Step 32

Go to Step 23

19

Check for restrictions between the intake manifold port the vacuum check valve.

Did you complete the repair?

--

Go to Step 36

Go to Step 20

20
  1. Disconnect the vacuum hose at the intake manifold.
  2. Using a vacuum gage at the intake manifold, measure and record the vacuum signal at engine Idle.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

--

Go to Diagnostic Starting Point - Engine Mechanical

21

Disconnect the vacuum pipe from the left exhaust flow control valve . The left valve will open.

Did the right exhaust flow control valve also fully OPEN?

--

Go to Step 34

Go to Step 22

22

Disconnect the vacuum pipe from the left exhaust flow control valve.

Did the both exhaust flow control valves fully OPEN?

--

Go to Step 33

Go to DTC P166A

23
  1. Disconnect the reservoir tank to flow control valves pipe from the vacuum solenoid.
  2. Using a vacuum gage , measure and record the vacuum signal at engine idle from the vacuum solenoid.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to Step 33

Go to Step 32

24
  1. Disconnect the vacuum check valve from the front chassis vacuum pipe, located near the brake booster.

    2. Important: If the O-ring is damaged, the exhaust tail pipe flow control vacuum check valve and hose will need to be replaced. Refer to Exhaust Tail Pipe Flow Control Vacuum Check Valve and Hose Replacement .

  2. Inspect the O-ring.
  3. Using a vacuum gage, measure and record the vacuum signal at engine Idle from the vacuum check valve.
  4. Clamp off the rubber hose forward of the vacuum check valve.

Does the vacuum remain steady for 30 seconds?

--

Go to Step 25

Go to Step 29

25
  1. Remove the clamp.
  2. Remove the vacuum gage.
  3. Connect Quick the vacuum check valve to front chassis pipe.
  4. Disconnect the vacuum pipe from the reservoir Tank.
  5. Using a J 35555 apply vacuum to the reservoir tank.

Does the vacuum gage read within the specified range for 30 seconds?

16-30 in Hg (54-102 kPa)

Go to Step 26

Go to Step 35

26
  1. Connect the vacuum line to the vacuum tank.
  2. Using a vacuum gage, tee into the vacuum lines at the left exhaust flow control valve.
  3. Use a scan tool to command the exhaust flow control solenoid ON.
  4. View both exhaust flow control valves from the rear of the vehicle.
  5. Have an assistant depress the accelerator pedal to the floor and immediately release the pedal.

Does the vacuum gage read within the specified range?

16-30 in Hg (54-102 kPa)

Go to DTC P166A

Go to Step 27

27

Isolate a small leak in the following locations.

    • Intake manifold to vacuum line connection
    • Quick connect connectors
    • Vacuum check valve line connectors
    • Vacuum storage tank connection
    • Vacuum solenoid connections
    • Exhaust flow control valve connections

Did you complete the repair?

--

Go to Step 36

--

28

Replace the exhaust flow control valve. Refer to Exhaust Muffler Replacement - Left Side or Exhaust Muffler Replacement - Right Side .

Did you complete the repair?

--

Go to Step 36

--

29

Replace the engine vacuum line assembly. Refer to Exhaust Tail Pipe Flow Control Vacuum Check Valve and Hose Replacement .

Did you complete the repair?

--

Go to Step 36

--

30

Replace the forward chassis vacuum line. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Chassis Front .

Did you complete the repair?

--

Go to Step 36

--

31

Replace the vacuum line between quick connect 3 and quick connect 4. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Chassis Rear .

Did you complete the repair?

--

Go to Step 36

--

32

Replace the solenoid vacuum line. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Reservoir Tank to Valve Solenoid .

Did you complete the repair?

--

Go to Step 36

--

33

Replace the vacuum line between the vacuum solenoid and exhaust flow control valves. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Replacement - Valve Solenoid to Control Valves .

Did you complete the repair?

--

Go to Step 36

--

34

Replace the vacuum solenoid. Refer to Exhaust Tail Pipe Flow Control Valve Solenoid Replacement

Did you complete the repair?

--

Go to Step 36

--

35

Replace the vacuum storage tank. Refer to Exhaust Tail Pipe Flow Valve Vacuum Pipe Reservoir Tank Replacement .

Did you complete the repair?

--

Go to Step 36

--

36

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2