GM Service Manual Online
For 1990-2009 cars only

Object Number: 323446  Size: MF
ABS Components
Antilock Brake System Schematics

Circuit Description (DTC C0265/C0266)

The pump motor relay supplies power to all eight solenoid coils (four isolation solenoid coils and four dump solenoid coils) and the pump motor when the ABS is required. The relay and the eight solenoid coils are located within the EBCM.

Conditions for Setting the DTC (DTC C0265)

    • The EBCM microprocessor commands the relay on
    • Low voltage exists on all eight solenoid driver circuits when high voltage is expected (the solenoid is not energized)

Conditions for Setting the DTC (DTC C0266)

    • The ABS bulb check is complete
    • High voltage exists on the eight solenoid circuits when all are expected to be low (the relay is not commanded on)

Action Taken When the DTC Sets

    • The ABS indicator lamp turns on
    • The ABS disables

DTCs C0265-C0266 are Ignition Latched DTCs, which indicates that the above actions remain true until the ignition is turned to OFF (even if the cause of the DTC is intermittent).

Conditions for Clearing the DTC

    • Repair the conditions responsible for setting the DTC
    • Use the Scan Tool Clear DTCs function

Diagnostic Aids (DTC C0265)

DTC C0265 usually sets because of an open relay coil or non-closable relay contacts. The relay is located within the EBCM. The relay is not serviceable. If the test does not repair the DTC, then replace the EBCM.

If DTC C0265 appears with other DTCs repair the other DTCs first. Clear all DTCs. Then run three function tests with the Scan Tool . Refer to this diagnostic chart if DTC C0265 resets.

Diagnostic Aids (DTC C0266)

DTC C0266 usually sets when the relay contacts are stuck closed. The relay is located within the EBCM. The relay is not serviceable. If the test does not repair the DTC, then replace the EBCM.

Test Description

The numbers below refer to the steps in the diagnostic table:

  1. This step checks the resistance of the ground circuit.

  2. This step checks the ignition voltage available to the EBCM.

Step

Action

Value(s)

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check

2

  1. Turn the ignition to OFF.
  2. Disconnect the 2-way EBCM harness connector from the EBCM.
  3. Inspect the connector for damage or corrosion that could cause a loss of power to the EBCM.

Is the connector in good condition?

--

Go to Step 3

Go to Step 7

3

Using the J 39200 , measure the resistance between terminal 2 of the 2-way EBCM harness connector and ground.

Is the resistance measurement within the specified range?

0-2 ohms

Go to Step  4

Go to Step 8

4

  1. Turn the ignition switch to RUN.
  2. Using a J 39200 , measure the voltage between terminal 1 of the 2-way EBCM harness connector and ground

Is the voltage measured equal to or greater than the specified value?

10 V

Go to Step 6

Go to Step 5

5

Inspect the 60-amp ABS MaxiFuse®.

Is the fuse open?

--

Go to Step 10

Go to Step 11

6

  1. Inspect the 2-way EBCM harness connector for poor terminal contact or corrosion. Inspect CKT 142 and CKT 150 for damage that may result in an open circuit. Repair damage if evident. Replace the terminals if poor contact or corrosion exists.
  2. Reconnect all the connectors.
  3. Using the Scan Tool clear all DTCs.
  4. Test drive the vehicle above 16 km/h (10 mph).
  5. Stop the vehicle and cycle the key on and off, drive the vehicle for an additional mile.

Does the DTC set as a current DTC?

--

Go to Step 9

Go to Diagnostic Aids

7

Repair the 2-way EBCM harness connector if necessary.

Refer to Connector Repairs .

Is the repair complete?

--

Go to Diagnostic System Check

--

8

Repair the open or the high resistance in CKT 150.

Refer to Wiring Repairs .

Is the repair complete?

--

Go to Diagnostic System Check

--

9

Replace the EBCM.

Refer to Electronic Brake Control Module Replacement .

Is the repair complete?

--

Go to Diagnostic System Check

--

10

Repair the short to ground in CKT 142.

Refer to Wiring Repairs .

Is the repair complete?

--

Go to Diagnostic System Check

--

11

Repair the open or high resistance in CKT 142.

Refer to Wiring Repairs .

Is the repair complete?

--

Go to Diagnostic System Check

--