GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Exhaust 🢒 Exhaust Brake Inoperative

Exhaust Brake Inoperative Without RPO LLY

Circuit Description

The exhaust brake system is used to provide additional braking when the vehicle is decelerating. The engine control module (ECM) controls exhaust brake operation based on various sensor inputs. The ECM energizes the exhaust brake relay for exhaust brake operation. On vehicles with an antilock brake system (ABS), the electronic brake control module (EBCM) controls the exhaust brake relay ground circuit to prevent exhaust brake operation when the ABS is active.

The exhaust brake relay energizes the telltale lamp on the driver information center and the exhaust brake actuator control solenoid (EBACS) valve. The EBACS valve allows compressed air from the auxiliary air system to move the exhaust brake actuator, rotating the exhaust brake to the closed position. When the air is released, a spring in the actuator returns the exhaust brake to the open position.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if there is an air leak causing the air pump to run continuously.

    2.

  2. This step determined if the problem is in the exhaust brake control circuits. If the telltale illuminates, the ECM is energizing the exhaust brake relay.

    3.

  3. This step determines if there is a leak in the exhaust brake system after the EBACS valve.

    4.

  4. This step determines if the ECM is receiving the request from the exhaust brake switch on the instrument panel.

    5.

  5. This step determines whether the air pump is operating, or if there is a blockage in the air lines to the exhaust brake.

Step

Action

Yes

No

Schematic Reference: Engine Exhaust Brake Schematics

1

Did you perform the Diagnostic Starting Point - Exhaust Brake?

Go to Step 2

Go to Diagnostic Starting Point - Engine Exhaust Brake

2

Drive the vehicle and engage the exhaust brake under normal exhaust brake operating conditions.

Does the exhaust brake engage when commanded ON during normal operation?

Go to Intermittent Conditions in Engine Controls - 6.6L (LB7)

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Does the auxiliary air compressor run constantly?

Go to Auxiliary Air Compressor Always On in Air Compressor - Auxiliary

Go to Step 4

4

Command the exhaust brake ON and OFF with a scan tool.

Does the exhaust brake indicator on the instrument panel turn ON and OFF when commanded?

Go to Step 5

Go to Step 15

5

Command the exhaust brake ON and OFF with a scan tool.

Does the exhaust brake actuator control solenoid (EBACS) valve click?

Go to Step 6

Go to Step 13

6

Command the exhaust brake ON and OFF with a scan tool.

Does air leak out of the exhaust brake air system when the exhaust brake is commanded ON?

Go to Step 35

Go to Step 7

7
  1. Observe the exhaust brake switch parameter with a scan tool.
  2. Turn the exhaust brake switch ON and OFF.

Does the exhaust brake switch change state?

Go to Step 8

Go to Engine Brake Switch Diagnosis

8

Caution: Refer to Eye Protection Caution in the Preface section.

Pull the auxiliary air tank drain valve open.

Does air come out under pressure?

Go to Step 9

Go to Auxiliary Air Compressor Inoperative in Air Compressor - Auxiliary

9

Caution: Refer to Safety Glasses and Compressed Air Caution in the Preface section.

  1. Turn OFF the ignition.
  2. Disconnect the auxiliary air compressor harness connector. Refer to Auxiliary Air Compressor Replacement .
  3. Discharge the air from the air tank.
  4. Disconnect the air line from the input side of the EBACS valve.
  5. Apply 724-827 kPa (105-125 psi) air pressure to the EBACS valve.
  6. Command the exhaust brake ON with a scan tool.

Does the exhaust brake close?

Go to Step 34

Go to Step 10

10
  1. Remove the compressed air from the exhaust brake actuator control valve.
  2. Disconnect the output air line from the EBACS valve.
  3. Apply 724-827 kPa (105-125 psi) air pressure to the input side of the EBACS valve.
  4. Command the exhaust brake ON with a scan tool.

Does air flow through the EBACS valve?

Go to Step 11

Go to Step 33

11

Caution: Refer to Hot Exhaust System Caution in the Preface section.

  1. Disconnect the exhaust brake from the exhaust brake actuator.
  2. Attempt to rotate the exhaust brake open and closed.

Does the exhaust brake move without resistance?

Go to Step 12

Go to Step 32

12
  1. Inspect the air line between the EBACS valve and the exhaust brake actuator for a restriction.
  2. Repair as necessary.

Did you find and correct the condition?

Go to Step 38

Go to Step 31

13
  1. Disconnect the EBACS valve.
  2. Turn ON the ignition, with the engine OFF.
  3. Connect a test lamp between the voltage supply circuit of the EBACS valve and the ground circuit of the EBACS valve.
  4. Command the exhaust brake ON and OFF with a scan tool.

Does the test lamp turn ON and OFF when commanded with a scan tool?

Go to Step 22

Go to Step 14

14

Probe the ground circuit of the EBACS valve harness connector with a test lamp connected to battery voltage.

Does the test lamp illuminate?

Go to Step 26

Go to Step 29

15
  1. Remove the exhaust brake relay.
  2. Probe the ignition 1 voltage circuit with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 16

Go to Step 28

16
  1. Probe the exhaust brake request circuit with a test lamp connected to a good ground.
  2. Command the exhaust brake ON with a scan tool.

Does the test lamp illuminate when commanded with a scan tool?

Go to Step 17

Go to Step 20

17

Probe the exhaust brake relay ground circuit with a test lamp connected to battery voltage.

Does the test lamp illuminate?

Go to Step 19

Go to Step 18

18

Does the vehicle have antilock brakes?

Go to Step 21

Go to Step 27

19
  1. Turn ON the ignition, with the engine OFF.
  2. Connect a 20-amp fused jumper wire between the ignition 1 voltage circuit of the exhaust brake relay harness connector and the voltage supply circuit of the exhaust brake relay harness connector.
  3. Observe the exhaust brake indicator on the instrument panel. Refer to Indicator/Warning Message Description and Operation in Instrument Panel, Gages, and Console.

Does the indicator illuminate?

Go to Step 23

Go to Step 26

20

Test the exhaust brake request circuit between the exhaust brake relay and the engine control module (ECM) for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 25

21

Test the antilock brake system (ABS) active circuit between the electronic brake control module (EBCM) and the exhaust brake relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 24

22

Test for an intermittent and for a poor connection at the EBACS valve. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 33

23

Test for an intermittent and for a poor connection at the exhaust brake relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 30

24

Test for an intermittent and for a poor connection at the electronic brake control module (EBCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 36

25

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 37

26

Repair the open in the EBACS valve voltage supply circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 38

--

27

Repair the open in the exhaust brake relay ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 38

--

28

Repair the open in the exhaust brake relay ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 38

--

29

Repair the open in the EBACS valve ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 38

--

30

Replace the exhaust brake relay. Refer to Engine Exhaust Brake Component Views .

Did you complete the replacement?

Go to Step 38

--

31

Replace the exhaust brake actuator. Refer to Engine Brake Actuator Replacement .

Did you complete the replacement?

Go to Step 38

--

32

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

Replace the exhaust brake. Refer to Engine Brake Replacement .

Did you complete the replacement?

Go to Step 38

--

33

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

Replace the EBACS valve. Refer to Exhaust Brake Actuator Control Solenoid Valve Replacement .

Did you complete the replacement?

Go to Step 38

--

34

Caution: Refer to Eye Protection Caution in the Preface section.

Replace the air line between the exhaust brake solenoid and the air tank.

Did you complete the replacement?

Go to Step 38

--

35

Caution: Refer to Eye Protection Caution in the Preface section.

Replace the leaking component.

Did you complete the replacement?

Go to Step 38

--

36

Replace the EBCM. Refer to Electronic Brake Control Module Replacement in Antilock Brake System.

Did you complete the replacement?

Go to Step 38

--

37

Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 6.6L (LB7).

Did you complete the replacement?

Go to Step 38

--

38

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2

Exhaust Brake Inoperative with RPO LLY

Circuit Description

The exhaust brake system is used to provide additional braking when the vehicle is decelerating. The engine control module (ECM) controls exhaust brake operation based on various sensor inputs. The ECM energizes the exhaust brake relay for exhaust brake operation. On vehicles with an antilock brake system (ABS), the electronic brake control module (EBCM) controls the exhaust brake relay ground circuit to prevent exhaust brake operation when the ABS is active.

The exhaust brake relay energizes the exhaust brake actuator control solenoid (EBACS) valve. The ECM energizes the telltale lamp on the driver information center when the exhaust brake system is active. The EBACS valve allows compressed air from the auxiliary air system to move the exhaust brake actuator, rotating the exhaust brake to the closed position. When the air is released, a spring in the actuator returns the exhaust brake to the open position.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if there is an air leak causing the air pump to run continuously.

    2.

  2. This step determined if the problem is in the exhaust brake control circuits. If the telltale illuminates, the ECM is energizing the exhaust brake relay.

    3.

  3. This step determines if there is a leak in the exhaust brake system after the EBACS valve.

    4.

  4. This step determines if the ECM is receiving the request from the exhaust brake switch on the instrument panel.

    5.

  5. This step determines whether the air pump is operating, or if there is a blockage in the air lines to the exhaust brake.

Step

Action

Yes

No

Schematic Reference: Engine Exhaust Brake Schematics

1

Did you perform the Diagnostic Starting Point - Exhaust Brake?

Go to Step 2

Go to Diagnostic Starting Point - Engine Exhaust Brake

2

Drive the vehicle and engage the exhaust brake under normal exhaust brake operating conditions.

Does the exhaust brake engage when commanded ON during normal operation?

Go to Intermittent Conditions in Engine Controls - 6.6L (LLY)

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Does the auxiliary air compressor run constantly?

Go to Auxiliary Air Compressor Always On in Air Compressor - Auxiliary

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Perform a visual and physical inspection of all of the exhaust brake components for the following conditions:
    3. • Loose electrical connections
    • Loose air line connections
    • Pinched, collapsed, or misrouted air lines
    • Road damaged, cut, split, or leaking air lines
    • Disconnected or damaged linkage

Did you find and correct the condition?

Go to Step 38

Go to Step 5

5

Command the exhaust brake ON and OFF with a scan tool.

Does the exhaust brake actuator control solenoid (EBACS) valve click?

Go to Step 6

Go to Step 13

6

Command the exhaust brake ON and OFF with a scan tool.

Does air leak out of the exhaust brake air system when the exhaust brake is commanded ON?

Go to Step 35

Go to Step 7

7
  1. Observe the exhaust brake switch parameter with a scan tool.
  2. Turn the exhaust brake switch ON and OFF.

Does the exhaust brake switch change state?

Go to Step 8

Go to Engine Brake Switch Diagnosis

8

Caution: Refer to Eye Protection Caution in the Preface section.

Pull the auxiliary air tank drain valve open.

Does air come out under pressure?

Go to Step 9

Go to Auxiliary Air Compressor Inoperative in Air Compressor - Auxiliary

9

Caution: Refer to Safety Glasses and Compressed Air Caution in the Preface section.

  1. Turn OFF the ignition.
  2. Disconnect the auxiliary air compressor harness connector. Refer to Auxiliary Air Compressor Replacement .
  3. Discharge the air from the air tank.
  4. Disconnect the air line from the input side of the EBACS valve.
  5. Apply 724-827 kPa (105-125 psi) air pressure to the EBACS valve.
  6. Command the exhaust brake ON with a scan tool.

Does the exhaust brake close?

Go to Step 34

Go to Step 10

10
  1. Remove the compressed air from the exhaust brake actuator control valve.
  2. Disconnect the output air line from the EBACS valve.
  3. Apply 724-827 kPa (105-125 psi) air pressure to the input side of the EBACS valve.
  4. Command the exhaust brake ON with a scan tool.

Does air flow through the EBACS valve?

Go to Step 11

Go to Step 33

11

Caution: Refer to Hot Exhaust System Caution in the Preface section.

  1. Disconnect the exhaust brake from the exhaust brake actuator.
  2. Attempt to rotate the exhaust brake open and closed.

Does the exhaust brake move without resistance?

Go to Step 12

Go to Step 32

12
  1. Inspect the air line between the EBACS valve and the exhaust brake actuator for a restriction.
  2. Repair as necessary.

Did you find and correct the condition?

Go to Step 38

Go to Step 31

13
  1. Disconnect the EBACS valve.
  2. Turn ON the ignition, with the engine OFF.
  3. Connect a test lamp between the voltage supply circuit of the EBACS valve and the ground circuit of the EBACS valve.
  4. Command the exhaust brake ON and OFF with a scan tool.

Does the test lamp turn ON and OFF when commanded with a scan tool?

Go to Step 22

Go to Step 14

14

Probe the ground circuit of the EBACS valve harness connector with a test lamp connected to battery voltage.

Does the test lamp illuminate?

Go to Step 15

Go to Step 29

15
  1. Remove the exhaust brake relay.
  2. Probe the ignition 1 voltage circuit with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 16

Go to Step 28

16
  1. Probe the exhaust brake request circuit with a test lamp connected to a good ground.
  2. Command the exhaust brake ON with a scan tool.

Does the test lamp illuminate when commanded with a scan tool?

Go to Step 17

Go to Step 20

17

Probe the exhaust brake relay ground circuit with a test lamp connected to battery voltage.

Does the test lamp illuminate?

Go to Step 19

Go to Step 18

18

Does the vehicle have antilock brakes?

Go to Step 21

Go to Step 27

19
  1. Turn ON the ignition, with the engine OFF.
  2. Connect the EBACS valve.
  3. Connect a 20-amp fused jumper wire between the ignition 1 voltage circuit of the exhaust brake relay harness connector and the voltage supply circuit of the exhaust brake relay harness connector.

Does the exhaust brake operate?

Go to Step 23

Go to Step 26

20

Test the exhaust brake request circuit between the exhaust brake relay and the engine control module (ECM) for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 25

21

Test the antilock brake system (ABS) active circuit between the electronic brake control module (EBCM) and the exhaust brake relay for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 24

22

Test for an intermittent and for a poor connection at the EBACS valve. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 33

23

Test for an intermittent and for a poor connection at the exhaust brake relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 30

24

Test for an intermittent and for a poor connection at the electronic brake control module (EBCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 36

25

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Step 37

26

Test for an open circuit in the EBACS valve voltage supply circuit. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 38

Go to Intermittent Conditions in Engine Controls - 6.6L (LLY)

27

Repair the open in the exhaust brake relay ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 38

--

28

Repair the open in the exhaust brake relay ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 38

--

29

Repair the open in the EBACS valve ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 38

--

30

Replace the exhaust brake relay. Refer to Engine Exhaust Brake Component Views .

Did you complete the replacement?

Go to Step 38

--

31

Replace the exhaust brake actuator. Refer to Engine Brake Actuator Replacement .

Did you complete the replacement?

Go to Step 38

--

32

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

Replace the exhaust brake. Refer to Engine Brake Replacement .

Did you complete the replacement?

Go to Step 38

--

33

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

Replace the EBACS valve. Refer to Exhaust Brake Actuator Control Solenoid Valve Replacement .

Did you complete the replacement?

Go to Step 38

--

34

Caution: Refer to Eye Protection Caution in the Preface section.

Replace the air line between the exhaust brake solenoid and the air tank.

Did you complete the replacement?

Go to Step 38

--

35

Caution: Refer to Eye Protection Caution in the Preface section.

Replace the leaking component.

Did you complete the replacement?

Go to Step 38

--

36

Replace the EBCM. Refer to Electronic Brake Control Module Replacement in Antilock Brake System.

Did you complete the replacement?

Go to Step 38

--

37

Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 6.6L (LB7).

Did you complete the replacement?

Go to Step 38

--

38

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2