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

Circuit Description

The system relay supplies battery voltage to all six valve solenoids. The EBCM applies the ground(s) needed for solenoid activation. The low side of each solenoid coil has a feedback circuit to the EBCM. When the relay is commanded off, feedback voltage is low. When the relay is commanded on and the solenoid is commanded off, feedback voltage is high.

Conditions for Running the DTC
    • The ignition is ON.
    • The vehicle speed is greater than 6 km/h (4 mph).

Conditions for Setting the DTC

C0265

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

C0266

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

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

Conditions for Clearing the DTC
    • The condition(s) responsible for setting the DTC is no longer present.
    • A scan tool is used 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. Refer to Testing for Intermittent Conditions and Poor Connections , Wiring Repairs and Connector Repairs in Wiring Systems.

C0266

An intermittent DTC C0266 can be set by several different internal EBCM problems. Replace the EBCM if DTC C0266 continues to set intermittently.

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 system 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 Function 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 from the EBCM, the harness connector which contains the battery positive voltage circuit.
  3. Connect a test lamp between the battery positive voltage circuit (at the harness connector) 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

Important: Use the scan tool in order to perform the Tire Size Calibration procedure.

Replace the 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 DTC.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK