GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Brakes 🢒 Hydraulic Brakes 🢒 DTC C0285

Circuit Description

The electronic brake control module (EBCM) monitors the function of the brake fluid flow switch to assure that the switch opens and closes properly.

Conditions for Running the DTC
    • The ignition is ON.
    • The EBCM has received a serial data message from the powertrain control module (PCM) indicating that the engine is running.

Conditions for Setting the DTC

The EBCM detects a closed brake fluid flow switch for greater than 1.6 seconds.

Action Taken When the DTC Sets
    • The brake warning 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 and you use the scan tool Clear DTCs function.

Diagnostic Aids

Ensure the power steering fluid is full and that the power steering belt is in good condition with proper tension. Any failure in the power steering system which effects steering or brake assist may cause this DTC to set.

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , Testing for Electrical Intermittents and to Wiring Repairs in Wiring Systems.

Test Description

The number below refers to the step number on the diagnostic table.

  1. If DTC C0285 does not set, DTC C0286 will set after the ignition is switched OFF. After the vehicle is repaired, use the scan tool to clear this DTC.

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

Ensure the power brake system is operating properly by performing the Brake Assist System Diagnosis .

Did you find and correct the condition?

Go to Step 8

Go to Step 4

4

  1. Use a scan tool in order to clear the DTC.
  2. Disconnect the hydromax flow switch harness connector.
  3. Start the engine and allow the engine to idle for 10 seconds.

Does DTC C0285 reset?

Go to Step 6

Go to Step 5

5

Replace the hydromax flow switch. Refer to Fluid Flow Switch Replacement .

Did you complete the replacement?

Go to Step 8

--

6
  1. Turn OFF the ignition.
  2. Disconnect the EBCM harness connector.
  3. Test the brake booster fluid flow switch signal circuit for the following.
    4. • A short to ground
    • A short to the hydromax flow switch ground circuit
    • 

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 7

7

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 8

--

8
  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