GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 Savana 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C0279

Circuit Description

The electronic brake control module (EBCM) uses the precharge pump in conjunction with the ABS pump to build hydraulic pressure for brake application during a vehicle stability enhancement system (VSES) event. Power and ground are both switched ON by the EBCM to energize the precharge pump motor.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0279 Pre-charge Pump Circuit Performance

Conditions for Running the DTC
    • The ignition is ON.
    • The precharge pump is activated during a VSES event or when the EBCM performs the power-up self-test. Refer to ABS Description and Operation for a complete description of the power-up self-test.

Conditions for Setting the DTC
    • The EBCM detects open precharge pump circuitry.
    • The EBCM detects shorted precharge pump circuitry.
    • The master cylinder pressure sensor signal does not increase sufficiently during a pressure-build event.

Action Taken When the DTC Sets
    • The EBCM disables the VSES.
    • The stability 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

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

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests if the EBCM is detecting open or shorted precharge pump motor circuitry.

    2.

  2. This step tests if the EBCM is capable of energizing the precharge pump motor.

Step

Action

Values

Yes

No

Schematic Reference: Antilock Brake System Schematics

Connector End View Reference: Antilock Brake System Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Use the scan tool to clear the DTCs.
  2. Turn OFF the ignition for 5 seconds.
  3. Turn ON the ignition.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn OFF the ignition.
  2. Disconnect the precharge pump motor harness connector.
  3. Use a connector test adapter kit to connect a test lamp between the precharge pump motor circuits.
  4. Turn ON the ignition.

Does the DTC reset?

--

Go to Step 9

Go to Step 4

4

  1. With the test lamp still connected, select the vehicle stability enhancement system (VSES) Special Functions menu on the scan tool.
  2. Select and perform the Pre-Charge Bleed.

Does the test lamp illuminate and then turn OFF when the Pre-Charge Bleed is performed?

--

Go to Step 5

Go to Step 11

5

Important: Always ensure that the master cylinder reservoir cap is in place and secure before turning ON the precharge pump.

  1. Reconnect the precharge pump motor harness connector.
  2. Use the scan tool to perform the Pre-Charge Bleed.

Does the precharge pump motor run?

--

Go to Step 6

Go to Step 8

6
  1. Observe the fluid in the master cylinder reservoir.
  2. Use the scan tool to perform the Pre-Charge Bleed.

When the precharge pump runs, can fluid be seen discharging back into the master cylinder reservoir?

--

Go to Step 13

Go to Step 7

7

Inspect the master cylinder reservoir, the brake fluid supply hose to the precharge pump inlet, and the precharge pump inlet port for any restriction that may cause the loss of fluid supply to the pump.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 15

8

Inspect for poor connections at the harness connectors of the precharge pump motor. 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 16

Go to Step 15

9

Important: Turn ON the ignition when testing for a short to voltage.

  1. Turn OFF the ignition.
  2. Disconnect the electronic brake control module (EBCM) harness connector.
  3. Test the precharge pump motor circuits for the following conditions:
    4. • An open
    • A short to ground
    • A short to voltage
    • Shorted together

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 10

10

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 16

Go to Step 13

11

Use a DMM to measure the resistance value of the precharge pump motor.

Does the resistance measure within the specified range?

0.3-1 ohms

Go to Step 12

Go to Step 14

12

Use the DMM to measure the resistance between the high side of the precharge pump motor and a good ground.

Does the resistance measure less than the specified value?

OL

Go to Step 14

Go to Step 13

13

Important: Following EBCM replacement, perform the set-up procedure for the EBCM and perform the Yaw Rate Reference Table Reset Procedure. Use the scan tool to perform the Tire Size Calibration procedure.

Replace the EBCM. Refer to Control Module References in Computer/Integrating Systems.

Did you complete the replacement?

--

Go to Step 16

--

14

Important: Following EBCM replacement, perform the set-up procedure for the EBCM and perform the Yaw Rate Reference Table Reset Procedure. Use the scan tool to perform the Tire Size Calibration procedure.

Replace the EBCM and the precharge pump assembly. Refer to Control Module References in Computer/Integrating Systems.

Did you complete the replacements?

--

Go to Step 16

--

15

Replace the precharge pump assembly. Refer to Brake Pressure Modulator Valve Pre-Charge Pump Replacement .

Did you complete the replacement?

--

Go to Step 16

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16
  1. Use the scan tool Clear All Class 2 DTCs function to clear all of the DTCs from all modules.
  2. Turn OFF the ignition for 5 seconds.
  3. Turn ON the ignition.
  4. 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