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Home >> Jeep >> 2005 >> Wrangler Rubicon, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 542 (Anti-Lock Brake System & Brake Controller - Electrical Diagnostics) >> DTC Troubleshooting >> Antilock Brake System & Electronic Stability Program >> C121E-Brake Pressure Sensor Comparative Performance >> Diagnostic Test

Diagnostic Test

WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
  1. 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

    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 

    1. Go To step  2).

    No 

    1. Refer ABS-INTERMITTENT CONDITION .
    2. Perform ABS VERIFICATION TEST - VER 1 .
  2. 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 

    1. Repair as necessary.
    2. Perform ABS VERIFICATION TEST - VER 1 .

    No 

    1. Go To step  3).
  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 

    1. Repair as needed.
    2. Perform ABS VERIFICATION TEST - VER 1 .

    No 

    1. Go To step  4).
  4. 4)  CHECK THE VOLTAGE ON THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT 
    Fig 1: Checking Brake Pressure Sensor Supply Circuit
    GC0026934Courtesy of DAIMLERCHRYSLER CORP.

    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 

    1. Go To step  8).

    No 

    1. Go To step  5).
  5. 5)  CHECK THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT FOR SHORT TO GROUND 
    Fig 2: Checking Brake Pressure Sensor Supply Circuit
    GC0026935Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition off.

    Disconnect the Anti-Lock Brake Module harness connector.

    Measure the resistance between ground and the (B83) Brake Pressure Sensor Supply circuit.

    Is the resistance below 5.0 ohms? 

    Yes 

    1. Repair the (B83) Brake Pressure Sensor Supply circuit for a short to ground.
    2. Perform ABS VERIFICATION TEST - VER 1 .

    No 

    1. Go To step  6).
  6. 6)  CHECK THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT FOR SHORT TO VOLTAGE 
    Fig 3: Checking Brake Pressure Sensor Supply Circuit
    GC0026936Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition on.

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

    Is there any voltage present? 

    Yes 

    1. Repair the (B83) Brake Pressure Sensor Supply circuit for a short to voltage.
    2. Perform ABS VERIFICATION TEST - VER 1 .

    No 

    1. Go To step  7).
  7. 7)  CHECK THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT FOR AN OPEN 
    Fig 4: Checking Brake Pressure Sensor Supply Circuit
    GC0026937Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition off.

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

    Is the resistance below 5.0 ohms? 

    Yes 

    1. Replace the Anti-Lock Brake Module in accordance with the Service Information.
    2. Perform ABS VERIFICATION TEST - VER 1 .

    No 

    1. Repair the (B83) Brake Pressure Sensor Supply circuit for an open.
    2. Perform ABS VERIFICATION TEST - VER 1 .
  8. 8)  CHECK THE RESISTANCE TO GROUND ON THE (B986) BRAKE PRESSURE RETURN CIRCUIT 
    Fig 5: Checking Brake Pressure Sensor Return Circuit
    GC0026938Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition off.

    Measure the resistance between the (B986) Brake Pressure Return circuit and ground.

    Is the resistance below 5.0 ohms? 

    Yes 

    1. Go To step  9).

    No 

    1. Repair the (B986) Brake Pressure Return circuit for an open.
    2. Perform ABS VERIFICATION TEST - VER 1 .
  9. 9)  CHECK THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT OUTPUT 
    Fig 6: Checking Brake Pressure Sensor Signal Circuit
    GC0026942Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition off.

    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 

    1. Go To step  13).

    No 

    1. Go To step  10).
  10. 10)  CHECK THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT FOR AN OPEN 
    Fig 7: Checking Brake Pressure Sensor Signal Circuit
    GC0026945Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition off.

    Disconnect the Anti-Lock Brake Module harness connector.

    Disconnect the Brake Pressure Sensor harness connector.

    Measure the resistance of the (B84) Brake Pressure Sensor Signal circuit.

    Is the resistance below 5.0 ohms? 

    Yes 

    1. Go To step  11).

    No 

    1. Repair the (B84) Brake Pressure Sensor Signal circuit for an open.
    2. Perform ABS VERIFICATION TEST - VER 1 .
  11. 11)  CHECK FOR A SHORT BETWEEN THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT AND THE (B83) BRAKE PRESSURE SENSOR SUPPLY CIRCUIT 
    Fig 8: Checking Brake Pressure Sensor Signal Circuit & Supply Circuit
    GC0026947Courtesy of DAIMLERCHRYSLER CORP.

    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 

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

    No 

    1. Go To step  12).
  12. 12)  CHECK FOR A SHORT BETWEEN THE (B84) BRAKE PRESSURE SENSOR SIGNAL CIRCUIT AND THE (B986) BRAKE PRESSURE SENSOR RETURN CIRCUIT 
    Fig 9: Checking Brake Pressure Sensor Signal Circuit & Return Circuit
    GC0026948Courtesy of DAIMLERCHRYSLER CORP.

    Measure the resistance between the (B84) Brake Pressure Sensor Signal and the (B986) Brake Pressure Sensor Return circuit.

    Is the resistance below 150 ohms? 

    Yes 

    1. Repair the (B84) Brake Pressure Sensor Signal and (B986) Brake Pressure Sensor Return circuits for a short together.
    2. Perform ABS VERIFICATION TEST - VER 1 .

    No 

    1. Go To step  13).
  13. 13)  CHECK THE (B45) STOP LAMP INHIBIT RELAY CONTROL OPERATION  
    Fig 10: Checking Stop Lamp Inhibit Relay Control Circuit
    GC0026949Courtesy of DAIMLERCHRYSLER CORP.

    Turn the ignition off.

    Disconnect the Anti-Lock Brake Module harness connector.

    Turn the ignition on.

    Measure the voltage on the (B45) Stop Lamp Inhibit Relay Control circuit while depressing and releasing the brake pedal.

    Does the voltage toggle from approximately 0 to 12 volts? 

    Yes 

    1. Replace the Anti-Lock Brake Module in accordance with the Service Information.
    2. Perform ABS VERIFICATION TEST - VER 1 .

    No 

    1. Repair as needed.
    2. Perform ABS VERIFICATION TEST - VER 1 .
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