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C121E



C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE





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.





Diagnostic Test

1. CHECK FOR A DTC C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE





NOTE: If any of the following DTC's are present they must be repaired before continuing

C122A-BRAKE PEDAL FORCE SWITCH CIRCUIT
C122B-BRAKE PEDAL FORCE SWITCH CIRCUIT PERFORMANCE
C1227-BRAKE PEDAL TRAVEL SENSOR CIRCUIT PERFORMANCE
C1228-BRAKE PEDAL TRAVEL SENSOR CIRCUIT LOW
C1229-BRAKE PEDAL TRAVEL SENSOR CIRCUIT HIGH

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: C121E-BRAKE PRESSURE SENSOR COMPARATIVE PERFORMANCE?

Yes

- Go To 2

No

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

No

- Go To 6

6. CHECK THE (B83) BRAKE PRESSURE SENSOR SUPPLY 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 (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 voltage.
- Perform ABS VERIFICATION 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.
Connect a jumper wire between the (B83) 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 VERIFICATION 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 below 5.O ohm?

Yes

- Go To 9

No

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

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





Turn the ignition off.
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 O.5O volts to 4.5 volts?

Yes

- Go To 13

No

- Go To 10

10. 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.
Connect a jumper 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

- Go To 11

No

- Repair the (B84) Brake Pressure Sensor Signal circuit for an open.
- Perform ABS VERIFICATION TEST VER 1. ABS Verification Test.

11. CHECK FOR A SHORT BETWEEN THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT AND THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT





Turn the ignition off.
Disconnect the Anti-Lock Brake Module harness connector.
Disconnect the Brake Pressure Sensor harness connector.
Measure the resistance between the (B84) Brake Pressure Sensor Signal circuit and the (B83) Brake Pressure Sensor Supply circuit.

Is the resistance below 150 ohms?

Yes

- Repair the (B83) Brake Pressure Sensor Supply and (B84) Brake Pressure Sensor Signal circuits for a short together.
- Perform ABS VERIFICATION TEST - VER 1. ABS Verification Test.

No

- Go To 12

12. CHECK FOR A SHORT BETWEEN THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT AND THE (B984) BRAKE PRESSURE SENSOR RETURN CIRCUIT





Turn the ignition off.
Disconnect the Anti-Lock Brake Module harness connector.
Disconnect the Brake Pressure Sensor harness connector.
Measure the resistance between the (B84) Brake Pressure Sensor Signal and the (B984) Brake Pressure Sensor Return circuit.

Is the resistance below 150 ohms?

Yes

- Repair the (B84) Brake Pressure Sensor Signal and (B984) Brake Pressure Sensor Return circuits for a short together.
- Perform ABS VERIFICATION TEST VER 1. ABS Verification Test

No

- Go To 13

13. CHECK THE (B121) STOP LAMP INHIBIT RELAY CONTROL OPERATION





Turn the ignition off.
Disconnect the Anti-Lock Brake Module harness connector.
Turn the ignition on.
Measure the voltage on the (B121) Stop Lamp Inhibit Relay Control circuit while depressing and releasing the brake pedal.

Does the voltage toggle from approximately 0 to 12 volts?

Yes

- Go To 14

No

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

14. CHECK THE (B137) BRAKE PEDAL TRAVEL SENSOR SIGNAL CIRCUIT VOLTAGE OUTPUT





Turn the ignition off.
Turn the ignition on.
While back probing, measure the voltage of the (B137) Brake Pedal Travel Sensor Signal circuit at the Brake Pedal Travel Sensor harness connector while depressing and releasing the brake pedal.

Is the voltage between O.15 volts to 4.85 volts?

Yes

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

No

- Replace the Brake Pedal Travel Sensor.
- Perform ABS VERIFICATION TEST VER 1. ABS Verification Test.
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