GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Chevrolet T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC C0272

Circuit Description

The electronic brake control module (EBCM) monitors the HydroMax assist relay and the HydroMax motor for electrical continuity.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The EBCM detects open Hydromax assist relay contacts while the relay is energized.

OR:

The EBCM detects an open Hydromax pump motor or pump motor circuit.

Action Taken When the DTC Sets
    • The service brake soon indicator turns ON.
    • A fast rate audible chime turns ON.

Conditions for Clearing the DTC

The conditions for setting the DTC are no longer present.

Diagnostic Aids
    • Check the following Underhood Fuse Block fuses for an open. The ABS-2 Fuse 40A, ABS-3 Fuse 40A, and ABS-1 Fuse 40A. These are all EBCM power supply circuits. Refer to Power Distribution Schematics .
    • Test the following Underhood Fuse Block EBCM power supply circuits for a short to ground, or open/high resistance. Circuit 1642 battery positive voltage, circuit 42 battery positive voltage circuit 442 battery positive voltage. Refer to Power Distribution Schematics .
    •  Inspect the 10A Hydromax fuse for an open.
    • Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to Testing for Electrical Intermittents , Testing for Intermittent Conditions and Poor Connections , Wiring Repairs and Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Listen for an audible click when the brake pedal is pressed and released.

    2.

  2. This step tests whether or not the EBCM is able to energize the hydromax relay.

    3.

  3. This step tests for voltage supplied to the hydromax pump motor when the hydromax relay is energized.

Step

Action

Yes

No

Schematic Reference: Brake Warning System Schematics

1

Did you perform the Hydraulic Brake Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Hydraulic Brakes

2
  1. Use a scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC set?

Go to Step 3

Go to Diagnostic Aids

3

Press the brake pedal.

Does the hydromax pump motor run when the brake is applied?

Go to Step 14

Go to Step 4

4

Press and release the brake pedal several times.

Does the hydromax relay click each time the brake pedal is pressed and released?

Go to Step 7

Go to Step 5

5

  1. Disconnect the hydromax relay harness connector.
  2. Connect a test lamp between the hydromax brake switch signal circuit and the brake booster fluid flow switch signal circuit.
  3. Press the brake pedal.

Does the test lamp illuminate when the brake pedal is pressed?

Go to Step 12

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Disconnect the EBCM harness connector.
  3. Test the hydromax brake switch signal circuit and the brake booster fluid flow switch signal 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 17

Go to Step 15

7

  1. Disconnect the hydromax pump motor harness connector.
  2. Connect a test lamp across the hydromax pump motor harness connector.
  3. Press the brake pedal.

Does the test lamp illuminate when the brake pedal is pressed?

Go to Step 10

Go to Step 8

8

Test the battery positive voltage circuit to the hydromax relay 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 17

Go to Step 9

9

Test the brake booster pump motor supply voltage circuit and the hydromax pump motor ground circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 12

10

Inspect for poor connections at the harness connector of the hydromax pump motor. 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 17

Go to Step 11

11

Replace the hydromax pump motor. Refer to Power Brake Booster Pump Replacement .

Did you complete the replacement?

Go to Step 17

--

12

Inspect for poor connections at the harness connector of the hydromax 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 17

Go to Step 13

13

Replace the hydromax relay.

Did you complete the replacement?

Go to Step 17

--

14

Turn the ignition off and test the hydromax motor feedback circuit for an open between terminal 10 of the EBCM connector and terminal A of the pump motor connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 17

Go to Step 15

15

Inspect for poor connections at the harness connector of 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 17

Go to Step 16

16

Important: Following EBCM replacement, use the scan tool to perform the Tire Size/Wheel Base Calibration procedure.

Replace the EBCM. Refer to Electronic Brake Control Module Replacement in Antilock Brake System.

Did you complete the replacement?

Go to Step 17

--

17
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 3

System OK