GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Brakes 🢒 Hydraulic Brakes 🢒 DTC C0286 or C086

Circuit Description

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

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0286 Fluid Flow Switch Circuit High

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The EBCM detects an open fluid flow switch for 4.4 seconds.

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 and you use the scan tool Clear DTCs function.

Diagnostic Aids
    • This DTC may be caused by a fluid flow switch that sticks open intermittently.
    • The ground circuit 151 of the park brake booster fluid flow switch should be checked for an intermittent or an open.
    • Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to the following:
       -  Testing for Electrical Intermittents
       -  Testing for Intermittent Conditions and Poor Connections
       -  Wiring Repairs
       -  Connector Repairs

Step

Action

Yes

No

Schematic Reference: Brake Warning System Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Use a scan tool to clear the DTCs.
  2. Start the engine and allow the engine to idle for 10 seconds.
  3. Turn OFF the ignition for 10 seconds.
  4. Turn ON the ignition.

Does the DTC set?

Go to Step 3

Go to Diagnostic Aids

3
  1. Use a scan tool to clear the DTC.
  2. Disconnect the fluid flow switch harness connector.
  3. Connect a test lamp between the hydromax brake switch signal circuit and a good ground.
  4. Start the engine and while allowing the engine to idle, observe the test lamp.

Does the test lamp blink ON and OFF?

Go to Step 4

Go to Step 6

4

Inspect for poor connections at the harness connector of the fluid flow switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 5

5

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

Did you complete the replacement?

Go to Step 8

--

6

Test the brake booster fluid flow switch signal circuit for an open between the fluid flow switch harness connector and the nearest splice. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 7

7

Replace the electronic brake control module (EBCM). Refer to Electronic Brake Control Module Replacement .

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