GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 GMC C Pickup - 2WD 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C0265 or C0266 and C065 C066 EBCM Relay Circuit

Circuit Description

The EBCM internal relay supplies battery voltage to all six valve solenoids and the pump motor. The low side of each solenoid coil has a feedback circuit to the EBCM microprocessor. When the relay is commanded off, the feedback voltage is low. When the relay is commanded on, the feedback voltage is high.

Conditions for Running the DTC
    • The ignition is ON.
    • The ABS bulb check is complete.
    • The vehicle is moving at a speed greater than 5 km/h (3 mph).

Conditions for Setting the DTC

C0265

The EBCM microprocessor detects low feedback voltage from all of the valve solenoids when the relay is commanded on.

C0266

The EBCM microprocessor detects high feedback voltage from all of the valve solenoids when the relay is commanded off.

Action Taken When the DTC Sets
    • The ABS and BRAKE indicators are commanded on.
    • The ABS and DRP are disabled for the remainder of the ignition cycle.
    • The EBCM aborts all other self-tests for components that are powered by the relay (DTC C0265 only).

Conditions for Clearing the DTC
    • Repair the condition(s) responsible for setting the DTC.
    • Use a scan tool in order to clear the DTC.

Diagnostic Aids

C0265

An intermittent DTC C0265 may be caused by a problem in the battery positive voltage circuit wiring or connection to the EBCM.

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Inspect for the following:

    • Backed out terminals
    • Improper mating
    • Broken locks
    • Corrosion
    • Improperly formed or damaged terminals
    • Poor terminal-to-wiring connections
    • Physically damaged wiring
    • Wiring broken inside the insulation

C0266

An intermittent DTC C0266 can be set by a number of internal EBCM problems. If DTC C0266 continues to set intermittently, replace the EBCM.

Test Description

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

  1. This step tests if the battery positive voltage circuit can supply adequate power to the EBCM internal relay.

Step

Action

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the ABS Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check

2
  1. Use a scan tool in order to clear the DTC(s).
  2. Use the scan tool in order to perform an ABS Relay Test.

Does DTC C0266 set?

Go to Step 7

Go to Step 3

3

Does DTC C0265 set?

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn the ignition OFF.
  2. Disconnect connector C2 from the EBCM.
  3. Connect a test lamp between the battery positive voltage circuit at connector C2 and a good ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 5

5

Repair the open in the battery positive voltage circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

--

6

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 8

Go to Step 7

7

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

Important: Perform the Tire Size Calibration procedure. Refer to Scan Tool Diagnostics

Did you complete the replacement?

Go to Step 8

--

8
  1. Use a scan tool in order to clear the DTC.
  2. Use the scan tool in order to perform an ABS Relay Test.

Does the DTC set?

Go to Step 4

System OK