Buick Regal: DTC C0126

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Refer to Diagnostic Procedure Instructions for an overview of each diagnostic category.

DTC Descriptor

DTC C0126

Brake Fluid Level Sensor Circuit

For symptom byte information refer to Symptom Byte List.

Diagnostic Fault Information

Circuit/System Description

The brake fluid level switch monitors the level of the brake fluid in the brake fluid reservoir. When the brake fluid level switch input closed, the electronic brake control module will set the DTC.

Conditions for Running the DTC

Ignition ON/Vehicle in Service Mode/Vehicle in Service Mode.

Conditions for Setting the DTC

• Low brake fluid level is detected for 5 s.
• An open is detected on the ground circuit.
• An open or short to voltage is detected on the signal circuit.

Action Taken When the DTC Sets

• The electronic brake control module disables the traction control and stability control for the duration of the ignition cycle.
• The traction control/stability control-active indicator turns ON.
• The brake warning indicator turns ON.

Conditions for Clearing the DTC

The condition for setting the DTC is no longer present.

Reference Information

Schematic Reference

Hydraulic Brake Wiring Schematics

Connector End View Reference

Component Connector End View Index

Description and Operation

Hydraulic Brake System Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference

Refer to Control Module References for scan tool information.

Circuit/System Verification

1. Verify that the brake fluid level is above the minimum level.

• If low

Refer to Brake Fluid Loss.

• Go to next step: If above minimum level

2. Refer to Circuit/System Testing.

Circuit/System Testing

1. Ignition OFF/Vehicle OFF and all vehicle systems OFF, disconnect the harness connector at the B20 Brake Fluid Level Switch. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 10 Ω between the ground circuit terminal 2 and ground.

• If 10 Ω or greater

1. Ignition OFF/Vehicle OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, repair the open/high resistance in the ground connection.

• Go to next step: If less than 10 Ω

3. Ignition ON/Vehicle in Service Mode.

4. Verify the scan tool Brake Fluid Level Sensor parameter is OK.

• If the parameter is not OK

1. Ignition OFF/Vehicle OFF/Vehicle OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
2. Test for infinite resistance between the signal circuit terminal 1 and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • If infinite resistance, replace the K17 Electronic Brake Control Module.

• Go to next step: If the parameter is OK

5. Ignition OFF/Vehicle OFF.

6. Install a 3 A fused jumper wire between the signal circuit terminal 1 and ground.

7. Ignition ON/Vehicle in Service Mode.

8. Verify the scan tool Brake Fluid Level Sensor parameter is Low.

• If the parameter is not Low

1. Ignition OFF/Vehicle OFF, disconnect the harness connector at the K17 Electronic Brake Control Module, ignition ON.
2. Test for less than 1 V between the signal circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • Go to next step: If less than 1 V.
3. Test for less than 2 Ω in the signal circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K17 Electronic Brake Control Module.

• Go to next step: If the parameter is Low

9. Test or replace the B20 Brake Fluid Level Switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Refer to Control Module References for electronic brake control module replacement, programming and setup.

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