Exhaust Brake Indicator Lamp Inoperative with RPO LLY
Diagnostic Fault Information
Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit/System Description
Ground is supplied to the exhaust brake indicator lamp. The engine control module (ECM) turns the lamp ON by supplying power to the lamp supply circuit.
Reference Information
Schematic Reference
Engine Exhaust Brake Schematics
Connector End View Reference
Engine Control Module Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
The exhaust brake lamp should turn ON when the exhaust brake is active, and turn OFF when the exhaust brake is not active.
Circuit/System Testing
Disconnect the ECM and jumper the exhaust brake lamp voltage circuit to voltage through a fused jumper.
| ⇒ | If the jumper fuse opens, repair the short to ground in the voltage supply circuit. |
| ⇒ | If the lamp illuminates, replace the ECM. |
| ⇒ | If the lamp does not illuminate, test the voltage and ground circuits of the exhaust brake indicator lamp for an open, or a faulty indicator bulb. |
Repair Instructions
Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM and instrument panel cluster (IPC) replacement, setup, and programming
Exhaust Brake Indicator Lamp Inoperative 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 ECM energizes the telltale lamp on the driver information center (DIC). 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 | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Exhaust Brake Schematics | ||||
1 | 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 2 | |
2 | Does the exhaust brake indicator illuminate during exhaust brake operation? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
3 |
Does the exhaust brake telltale lamp illuminate? | -- | Go to Step 9 | Go to Step 4 |
4 |
Is the voltage displayed on the DMM more than the specified value? | 10 V | Go to Step 5 | Go to Step 6 |
5 |
Is the resistance displayed on the DMM more than the specified value? | 5 ohms | Go to Step 10 | Go to Step 8 |
6 | Test the exhaust brake telltale indicator lamp request circuit for an open, high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 7 |
7 | Test the exhaust brake telltale indicator lamp ground circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8 |
8 | 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 . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 |
9 | 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 13 | Go to Step 12 |
10 | Repair the high resistance in the exhaust brake telltale indicator lamp request circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 13 | -- |
11 | Replace the telltale circuit board. Refer to Telltale Circuit Board Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 13 | -- |
13 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2 |
