C121D

C121D-BRAKE PRESSURE SENSOR CIRCUIT





When Monitored:

With the ignition on.

Set Condition:

When the Anti-Lock Brake Module indicates that the Brake Pressure Sensor Signal is out of range.

Possible Causes

TERMINAL/CONNECTOR/WIRING HARNESS DAMAGE
AIR IN BRAKE SYSTEM/WORN MECHANICAL COMPONENTS
(B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT SHORTED TO VOLTAGE, ROUND, OR OPEN
(B984) BRAKE PRESSURE SENSOR RETURN CIRCUIT SHORTED TO VOLTAGE, ROUND, OR OPEN
(B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT SHORTED TO VOLTAGE, GROUND, OR OPEN
BRAKE PRESSURE SENSOR
ANTI-LOCK BRAKE MODULE

Diagnostic Test

1. CHECK FOR A DTC C121D-BRAKE PRESSURE SENSOR CIRCUIT





NOTE: This DTC must be active for the results of this test to be valid.

Turn the ignition on.

With the scan tool, read and record DTC's.

With the scan tool, read and record Freeze Fame information.

With the scan tool, erase DTC's.

Start the engine.

Depress and release the brake pedal.

With the scan tool, read and record DTC's.

Does the scan tool display: C121D-BRAKE PRESSURE SENSOR CIRCUIT?

Yes

- Go To 2

No

- Refer to the INTERMITTENT CONDITION diagnostic procedure. Testing and Inspection.
- Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

2. CHECK THE TERMINALS/CONNECTORS/WIRING HARNESS FOR DAMAGE





Check all related wiring for bruised, chafed, pierced, or partially broken wires.

Check all related connectors for broken, bent, pushed out or corroded terminals.

Were any problems found?

Yes

^ Repair as necessary.
^ Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test.

No

^ Go To 3

3. CHECK FOR AIR IN BRAKE SYSTEM AND WORN MECHANICAL COMPONENTS

NOTE: Before continuing the brake system must be bled to verify there is no air in the brake system.

NOTE: Visually inspect for worn brake linings, undersized rotors, binding or frozen calipers.

Was there any air in the brake system or base brake issues found?

Yes

^ Repair as needed.
^ Perform ABS VERIEICATION TEST - VER 1. ABS Verification Test.

No

- Go To 4

4. CHECK THE VOLTAGE ON THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT





Turn the ignition off.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition on.

Measure the voltage of the (B83) Brake Pressure Sensor Supply circuit.

Is the voltage above 4 volts?

Yes

- Go To 8

No

^ Go To 5

5. CHECK THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT FOR SIIORT TO GROUND





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition on.

Using a 12-volt test light connected to 12-volts, check the (B83) Brake Pressure Sensor Supply circuit.

Does the test light illuminate brightly?

Yes

^ Repair the (B83) Brake Pressure Sensor Supply circuit for a short to ground.
^ Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

- Go To 6

6. CHECK THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT FOR SIIORT TO VOLTAGE





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition on.

Using a 12-volt test light connected to ground, check the (B83) Brake Pressure Sensor Supply circuit.

Does the test light illuminate brightly?

Yes

^ Repair the (B 83) Brake Pressure Sensor Supply circuit for a short to voltage.
^ Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

- Go To 7

7. CHECK THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT FOR AN OPEN





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition off.

Connect a jumper wire between the (B 83) Brake Pressure Sensor Supply circuit and ground.

Using a 12-volt test light connected to 12-volts, check the (B83) Brake Pressure Sensor Supply circuit.

Does the test light illuminate brightly?

Yes

- Replace the Anti-Lock Brake Module.
- Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

- Repair the (B83) Brake Pressure Sensor Supply circuit for an open.
- Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test.

8. CHECK THE RESISTANCE TO GROUND ON THE (B984) BRAKE PRESSURE RETURN CIRCUIT





Turn the ignition off.

Disconnect the Brake Pressure Sensor harness connector.

Measure the resistance between the (B984) Brake Pressure Return Circuit and ground.

Is the resistance above 5.0 ohm?

Yes

- Go To 12

No

- Go To 9

9. CHECK THE (B984) BRAKE PRESSURE SENSOR RETURN CIRCUIT FOR SHORT TO GROUND





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Using a 12-volt test light connected to 12-volts, check the (B984) Brake Pressure Sensor Return circuit.

Does the test light illuminate brightly?

Yes

- Repair the (B984) Brake Pressure Sensor Return circuit for a short to ground.
- Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

- Go To 1O

10. CHECK THE (B984) BRAKE PRESSURE SENSOR RETURN CIRCUIT FOR SHORT TO VOLTAGE





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition on.

Using a 12-volt test light connected to ground check the (B984) Brake Pressure Sensor Return circuit.

Does the test light illuminate brightly?

Yes

^ Repair the (B984) Brake Pressure Sensor Return circuit for a short to voltage.
- Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test.

No

- Go To 11

11. CHECK THE (B984) BRAKE PRESSURE SENSOR RETURN CIRCUIT FOR AN OPEN





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition off.

Connect a jumper wire between the (B 984) Brake Pressure Sensor Return circuit and ground.

Using a 12-volt test light connected to 12-volts, check the (B984) Brake Pressure Sensor Return circuit

Does the test light illuminate brightly?

Yes

^ Replace the Anti-Lock Brake Module.
^ Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

^ Repair the (B984) Brake Pressure Sensor Return circuit for an open.
- Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test.

12. CHECK THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT OUTPUT





Turn the ignition off.

Reconnect the Anti-Lock Brake Module harness connector. Reconnect the Brake Pressure Sensor harness connector.

Start the engine.

While back probing measure the voltage of the (B84) Brake Pressure Sensor Signal circuit at the Brake Pressure Sensor harness connector while depressing and releasing the brake pedal.

Is the voltage between 0.50 volts to 4.55 volts?

Yes

^ Replace the Anti-Lock Brake Module.
^ Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

- Go To 13

13. CHECK THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO GROUND





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition off.

Using a 12-volt test light connected to 12-volts~ check the (B84) Brake Pressure Sensor Signal circuit.

Does the test light illuminate brightly?

Yes

^ Repair the (B84) Brake Pressure Sensor Signal circuit for a short to ground.
^ Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

^ Go To 14

14. CHECK THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition on.

Using a 12-volt test light connected to ground~ check the (B84) Brake Pressure Sensor Signal circuit.

Does the test light illuminate brightly?

Yes

^ Repair the (B 84) Brake Pressure Sensor Signal circuit for a short to voltage.
^ Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test.

No

^ Go To 15


15. CHECK THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT FOR AN OPEN





Turn the ignition off.

Disconnect the Anti-Lock Brake Module harness connector.

Disconnect the Brake Pressure Sensor harness connector.

Turn the ignition off.

Connect ajumper wire between the (B84) Brake Pressure Sensor Signal circuit and ground.

Using a 12-volt test light connected to 12-volts check the (B84) Brake Pressure Sensor Signal circuit.

Does the test light illuminate brightly?

Yes

^ Replace the Brake Pressure Sensor.
^ Perform ABS VLRIFICATION TEST - VER 1. ABS Verification Test.

No

^ Repair the (B 84) Brake Pressure Sensor Signal circuit for an open.
Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test.