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.
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This step determines if there is an air leak causing the air pump to run continuously.
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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.
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This step determines if there is a leak in the exhaust brake system after the EBACS valve.
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This step determines if the ECM is receiving the request from the exhaust brake switch on the instrument panel.
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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 System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls |
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 | Go to Step 3 |
Turn ON the ignition, with the engine OFF. Does the auxiliary air compressor run constantly? | Go to Step 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 |
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 | |
Does the exhaust brake switch change state? | Go to Step 8 | ||
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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 | ||
9 |
Caution: Refer to Safety Glasses and Compressed Air Caution in the Preface section.
Does the exhaust brake close? | Go to Step 34 | Go to Step 10 |
10 |
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.
Does the exhaust brake move without resistance? | Go to Step 12 | Go to Step 32 |
12 |
Did you find and correct the condition? | Go to Step 38 | Go to Step 31 |
13 |
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 |
Does the test lamp illuminate? | Go to Step 16 | Go to Step 28 |
16 |
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 |
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 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 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 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. 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 |
