Exhaust Brake Always On 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 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 - Engine Exhaust Brake? | Go to Step 2 | |
2 | Operate the vehicle and engage the exhaust brake. Does the exhaust brake operate normally? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
3 |
Does the exhaust brake actuator cycle ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 4 |
4 |
Does the exhaust brake actuator piston move to the open position? | Go to Step 5 | Go to Step 7 |
5 | Probe the exhaust brake request circuit of the exhaust brake relay harness connector with a test lamp connected to a good ground. Does the test lamp illuminate? | Go to Step 6 | Go to Step 15 |
6 |
Does the test lamp illuminate? | Go to Step 12 | Go to Step 17 |
7 |
Caution: Refer to Eye Protection Caution in the Preface section.
Does the exhaust brake move to the open position? | Go to Step 10 | Go to Step 8 |
8 |
Caution: Refer to Hot Exhaust System Caution in the Preface section.
Does the exhaust brake move without resistance? | Go to Step 9 | Go to Step 14 |
9 |
Caution: Refer to Eye Protection Caution in the Preface section.
Does the exhaust brake rotate to the open position? | Go to Step 11 | Go to Step 13 |
10 | Test for a short to voltage on the exhaust brake actuator control solenoid (EBACS) valve voltage supply circuit. Refer to Wiring Repairs . Did you find and correct the condition? | Go to Step 18 | Go to Step 11 |
11 | Inspect for a collapsed or restricted air line between the EBACS valve and the exhaust brake. Did you find and correct the condition? | Go to Step 18 | Go to Step 16 |
12 | Repair the short to voltage on the exhaust brake request circuit. Refer to Wiring Repairs . Did you complete the repair? | Go to Step 18 | -- |
13 | Replace the exhaust brake actuator. Refer to Engine Brake Actuator Replacement . Did you complete the replacement? | Go to Step 18 | -- |
14 |
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 18 | -- |
15 | Replace the exhaust brake relay. Refer to Engine Exhaust Brake Component Views . Did you complete the replacement? | Go to Step 18 | -- |
16 |
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 18 | -- |
17 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 18 | -- |
18 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 |
