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 System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
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 Step 3 | |
3 | Does the exhaust brake indicator illuminate during exhaust brake operation? | Go to Intermittent Conditions in Engine Controls - 7.8L | Go to Step 4 |
4 |
Does the test lamp illuminate when the exhaust brake is commanded ON? | Go to Step 5 | Go to Step 7 |
5 | Probe the ground circuit of the exhaust brake indicator in the telltale circuit board with a test lamp connected to battery voltage. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | Go to Step 6 | Go to Step 8 |
6 | Test for an intermittent and for a poor connection at the telltale circuit board. 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 10 | Go to Step 9 |
7 | Repair the open or high resistance in the EBACS valve voltage supply circuit between the splice and the telltale lamp circuit board. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 10 | -- |
8 | Repair the open or high resistance in the ground circuit of the exhaust brake indicator lamp. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 10 | -- |
9 | Replace the telltale circuit board. Refer to Telltale Circuit Board Replacement in Instrument Panel, Gages, and Console. Did you complete the replacement? | Go to Step 10 | -- |
10 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
