GM Service Manual Online
For 1990-2009 cars only

Exhaust Brake Indicator Lamp Inoperative 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

Go to Exhaust Brake Inoperative

2

Does the exhaust brake indicator illuminate during exhaust brake operation?

--

Go to Intermittent Conditions in Engine Controls - 6.6L

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM).
  3. Probe the exhaust brake telltale indicator lamp request circuit at the ECM harness connector with a 3-amp fused jumper wire connected to battery voltage. Refer to Wiring Repairs in Wiring Systems.

Does the exhaust brake telltale lamp illuminate?

--

Go to Step 9

Go to Step 4

4

  1. Ensure that the jumper wire remains connected.
  2. Disconnect the telltale circuit board connector. Refer to Engine Exhaust Brake Component Views .
  3. Probe the exhaust brake telltale lamp request circuit at the exhaust brake indicator lamp circuit board connector with a DMM connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.

Is the voltage displayed on the DMM more than the specified value?

10 V

Go to Step 5

Go to Step 6

5

  1. Remove the jumper wire from the ECM connector.
  2. Ensure that the ECM and the telltale circuit board remain disconnected.
  3. Measure the resistance of the exhaust brake telltale indicator lamp request circuit with a DMM. Refer to Circuit Testing in Wiring Systems.

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 in Wiring Systems.

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 in Wiring Systems.

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 in Wiring Systems.

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 in Wiring Systems.

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 in Wiring Systems.

Did you complete the repair?

--

Go to Step 13

--

11

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 13

--

12

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems 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