Engine Brake Switch Diagnosis 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.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Exhaust Brake Schematics | |||
1 | Did you perform the Diagnostic Starting Point - Exhaust Brake? | Go to Step 2 | |
2 |
Does the exhaust brake switch change state? | Go to Intermittent Conditions | Go to Step 3 |
3 | Does the exhaust brake switch parameter indicate ON? | Go to Step 4 | Go to Step 6 |
4 |
Does the exhaust brake switch indicate OFF? | Go to Step 13 | Go to Step 5 |
5 |
Does the test lamp illuminate? | Go to Step 11 | Go to Step 14 |
6 |
Does the exhaust brake switch indicate ON? | Go to Step 7 | Go to Step 8 |
7 |
Does the test lamp illuminate? | Go to Step 9 | Go to Step 12 |
8 | Test the exhaust brake request circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 15 | Go to Step 10 |
9 | Test for an intermittent and for a poor connection at the exhaust brake switch. 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 15 | Go to Step 13 |
10 | 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 15 | Go to Step 14 |
11 | Repair the short to ground in the exhaust brake switch request circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 15 | -- |
12 | Repair the open or high resistance in the ground circuit of the exhaust brake switch . Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 15 | -- |
13 | Replace the exhaust brake switch. Refer to Engine Brake Switch Replacement Did you complete the replacement? | Go to Step 15 | -- |
14 | Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls -- 6.6L Did you complete the replacement? | Go to Step 15 | -- |
15 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
Engine Brake Switch Diagnosis 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 ECM energizes the telltale lamp on the driver information center and the exhaust brake relay. The exhaust brake relay energizes 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.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Exhaust Brake Schematics | |||
1 | Did you perform the Diagnostic Starting Point - Exhaust Brake? | Go to Step 2 | |
2 |
Does the exhaust brake switch change state? | Go to Intermittent Conditions | Go to Step 3 |
3 | Does the exhaust brake switch parameter indicate ON? | Go to Step 4 | Go to Step 6 |
4 |
Does the exhaust brake switch indicate OFF? | Go to Step 13 | Go to Step 5 |
5 |
Does the test lamp illuminate? | Go to Step 11 | Go to Step 14 |
6 |
Does the exhaust brake switch indicate ON? | Go to Step 7 | Go to Step 8 |
7 |
Does the test lamp illuminate? | Go to Step 9 | Go to Step 12 |
8 | Test the exhaust brake request circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 15 | Go to Step 10 |
9 | Test for an intermittent and for a poor connection at the exhaust brake switch. 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 15 | Go to Step 13 |
10 | 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 15 | Go to Step 14 |
11 | Repair the short to ground in the exhaust brake switch request circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 15 | -- |
12 | Repair the open or high resistance in the ground circuit of the exhaust brake switch . Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 15 | -- |
13 | Replace the exhaust brake switch. Refer to Engine Brake Switch Replacement Did you complete the replacement? | Go to Step 15 | -- |
14 | Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 6.6L. Did you complete the replacement? | Go to Step 15 | -- |
15 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
