GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C-Series Medium Duty Truck B7 🢒 DTC 🢒 DTC C0269 or C0274 and C069 or C074

Circuit Description

The system relay is energized when the ignition is ON. The system relay supplies voltage to the valve solenoids and the pump motor. This voltage is referred to as the system voltage. The electronic brake control module (EBCM) microprocessor activates the valve solenoids by grounding the control circuit.

Conditions for Running the DTC
    • The ignition is ON.
    • The vehicle is experiencing an ABS event.

Conditions for Setting the DTC

C0269

The EBCM commands a dump solenoid ON for 9 consecutive seconds.

C0274

The EBCM commands an isolation solenoid ON for 120 consecutive seconds.

Action Taken When the DTC Sets
    • The EBCM disables the ABS.
    • The ABS indicator 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

If any other DTCs are set, repair those DTCs first. The most likely cause of DTC C0269 or DTC C0274 is a mechanical failure that causes a wheel to lock and remain locked. The DTCs may also set, conceivably, when the ABS is activated on surfaces that are nearly impossible to get traction on. If the DTC sets within these conditions, diagnosis of the ABS system is not necessary.

Test Description

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

  1. Using the scan tool in order to perform an ABS Function Test while applying firm and steady pressure to the brake pedal and observing how the pedal reacts determines if there is a mechanical malfunction inside the BPMV (i.e.; a dump valve stuck closed or an isolation valve stuck open).

Step

Action

Yes

No

1

Did you perform the ABS Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - ABS

2

  1. Install a scan tool.
  2. Use the scan tool in order to clear the DTCs.
  3. Use the scan tool in order to perform an ABS Function Test while applying firm and steady pressure to the brake pedal. Observe the brake pedal and ensure the pedal reacts as follows. The Time values used in the procedure below are approximate.
    4. 3.1. The pump motor activates for 0.5 seconds.
    3.2. The pedal drops to the floor for 2 seconds.
    3.3. The pedal pumps up for 2 seconds.
    3.4. The pedal drops approximately 1.25 cm (0.5 in) and then holds for 1 second.
    3.5. Steps 3.2, 3.3 and 3.4 repeat.
    3.6. Steps 3.2, 3.3 and 3.4 repeat.
    3.7. Step 3.2 repeats.
    3.8. Step 3.3 repeats.
    3.9. Step 3.2 repeats.
    3.10. Step 3.3 repeats.

Does the brake pedal react as described when the Function Test is performed?

Go to Diagnostic Aids

Go to Step 3

3

Replace the BPMV. Refer to Brake Pressure Modulator Valve Replacement .

Did you complete the replacement?

Go to Step 4

--

4

Use the scan tool in order to perform an ABS Function Test while applying firm and steady pressure to the brake pedal. Observe the brake pedal and ensure the pedal reacts as described in step 2.

Does the brake pedal react as described in step 2 when the Function Test is performed?

System OK

Go to Step 2