GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Exhaust 🢒 Exhaust Brake Inoperative

Exhaust Brake Inoperative with RPO LG4 or LF8

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 (DIC) 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 determines 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 (I/P).

    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: Exhaust System Schematics

1

Did you perform the Diagnostic Starting Point - Engine 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 Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

Turn ON the ignition, with the engine OFF.

Does the auxiliary air compressor run constantly?

Go to Auxiliary Air Compressor Always On

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

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 .

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 .

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 .

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 .

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 EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

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 .

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 .

Did you find and correct the condition?

Go to Step 38

Go to Testing for Intermittent Conditions and Poor Connections

27

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

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 .

Did you complete the repair?

Go to Step 38

--

29

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

Did you complete the repair?

Go to Step 38

--

30

Replace the exhaust brake relay.

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 .

Did you complete the replacement?

Go to Step 38

--

37

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

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 or LMM

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Typical Scan Tool Data

Exhaust Brake Switch

Circuit

Normal Range

Short to Ground

Open

Short to Voltage

Operating Conditions: Ignition ON, Engine OFF, Switch ON

Exhaust Brake Switch Signal

ON

ON

OFF

OFF¹

Ground

--

ON

OFF

OFF²

¹ When shorted to voltage, circuit will go open when switch is turned ON.

² When shorted to voltage, the weakest circuit will go open.

Circuit/System 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 commands the turbocharger vane position to maximum boost for exhaust brake operation. Any malfunction of the Turbocharger or related engine controls hardware will set a powertrain DTC. If the exhaust brake does not function properly and there are no DTCs, the exhaust brake switch and related circuit should be diagnosed.

Reference Information

Schematic Reference

Exhaust System Schematics

Connector End View Reference

Engine Control Module Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Circuit/System Verification
  1. Turn ON the ignition with the engine OFF.
  2. Turn the exhaust brake switch ON and OFF while observing the Exhaust Brake Switch parameter on the scan tool.
    3. ⇒The exhaust brake switch parameter should toggle ON and OFF as the switch is turned ON and OFF.

Circuit/System Testing
  1. Turn ON the ignition with the engine OFF.
  2. Turn the exhaust brake switch ON and OFF while observing the Exhaust Brake Switch parameter on the scan tool.
    3. ⇒If the Exhaust Brake Switch parameter indicates ON all of the time, test the exhaust brake switch signal circuit for an open, or a faulty switch.
  3. Disconnect the exhaust brake switch and jumper the exhaust brake switch signal circuit to ground with a fused jumper.
    4. ⇒If the Exhaust Brake Switch parameter indicates ON when the circuit is jumpered, test the exhaust brake switch ground circuit for an open, or a faulty exhaust brake switch.
    ⇒If the Exhaust Brake Switch parameter indicates OFF when the circuit is jumpered, test the exhaust brake switch signal circuit for an open, short to voltage, or fault ECM.

Component Testing
  1. Remove the exhaust brake switch from the vehicle.
  2. With a DMM, measure for no resistance between the ground and signal pins of the switch when the switch is in the ON position.
    3. ⇒If the switch has more than 0 ohm resistance when the switch is ON, replace the switch.
  3. With a DMM, measure for infinite resistance between the ground and signal pins of the switch when the switch is in the OFF position.
    4. ⇒If the switch has low resistance when the switch is OFF, replace the switch.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Engine Brake Switch Replacement
    •  Control Module References for ECM replacement, setup, and programming