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:
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests if the EBCM is detecting open or shorted precharge pump motor circuitry.
-
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? | -- | Go to Step 2 | |||||||||
2 |
Does the DTC reset? | -- | Go to Step 3 | Go to Diagnostic Aids | ||||||||
Does the DTC reset? | -- | Go to Step 9 | Go to Step 4 | |||||||||
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.
Does the precharge pump motor run? | -- | Go to Step 6 | Go to Step 8 | ||||||||
6 |
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 . 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.
Refer to Circuit Testing and Wiring Repairs . 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 . 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 . 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 . 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 | -- | ||||||||
16 |
Does the DTC reset? | -- | Go to Step 3 | System OK | ||||||||
