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DIAGNOSTIC TEST - NON-eBOOSTER BRAKE SYSTEM - PCM

PRELIMINARY DIAGNOSTIC CHECKS 

  1. Check the tire and wheel sizes. Mismatched tires and wheels can cause rationality DTCs to set.
  2. Check for any Service Bulletins, Star On-line Cases or ECU flash updates that apply for the DTC or symptom.
  3. Check for any Battery voltage DTCs in the BSCM. Low Battery voltage can cause DTCs.
  4. Circuit faults should typically be diagnosed before rationality/performance faults.

BRAKE PEDAL POSITION SENSOR CIRCUIT FAULTS (P057C, P057D): TECH TIP:  Typical three wire sensors must have voltage present on the 5-Volt Supply circuit to function properly. No voltage on the 5-Volt Supply circuit can cause the sensor to react one of two ways, depending on the type of sensor being used. The first is the sensor signal voltage can be stuck mid range (2.4-2.6 volts), and not change which can cause a performance fault. The second is the signal voltage can be stuck low (0 volts) since the ECU is using a pull-down signal.

  1. Check the sensor harness connector for proper connection at the BPP Sensor. Verify that the connector is completely plugged in and properly locked prior to disconnecting for testing. Disconnect the BPP Sensor harness connector and check for any pushed out, damaged, corroded or spread terminals.
  2. Measure the voltage on the 5-Volt Supply circuit with the ignition on. The voltage should measure above 4.9 volts.
    1. If voltage is present, continue to step 3.
    2. If no voltage is present at the harness connector, repair the 5-Volt Supply circuit for an open or high resistance.
  3. This step is designed to determine if the fault is being caused by a faulty sensor. Connect the special tool # 2064100081, (Electrical Test Lead Kit) to the BPP Sensor signal and 5-Volt Supply circuit at the BPP Sensor harness connector. A fused jumper can also be used for this step. Move the switch on the Electrical Test Lead Kit to the CLOSED position while either monitoring the voltage or fault screen on the scan tool. The voltage should read 5.0v if available, or the circuit high fault should be active. Next, connect the leads between the signal circuit and the sensor circuit at the BPP Sensor harness connector. The voltage should read 0v if available, or the circuit low fault should be active.
    NOTE:

    Since the BSCM uses a pull down signal, simply disconnecting the sensor harness connector should also give the same results.

    1. If the voltage or faults appear as described above, the BPP Sensor is most likely faulty.
    2. If the voltage remains at 0v and only the circuit low fault is active, continue to step 4.
  4. Disconnect the BSCM harness connector to isolate the circuits and check the sensor signal circuit for continuity to both chassis ground and the sensor ground circuit.
    1. If there is continuity to either, repair the signal circuit for a short to chassis ground or the sensor ground circuit.
    2. If the signal circuit is not shorted, continue to step 5.
  5. Measure the resistance of the sensor signal and sensor ground circuits. Typically the circuit resistance should be less than 5.0 Ohms.
    1. If there is an open or high resistance in either circuit, repair the signal circuit for an open or high resistance.
    2. If the temp sensor signal and ground circuits test good, use the wiring information to check all related harness connectors for pushed out, spread, corroded or dirty terminals before condemning BSCM. If no issues are found, replace the BSCM in accordance with the service information.

PCM SYSTEM PERFORMANCE FAULTS (P057B, C053D, C10F5):  The signal performance faults set when one of the following signals received from the BSCM is irrational when compared to the others. The rationality checks are only done during a driver initiated braking event, not during an autonomous braking event.

The Master Cylinder Pressure Sensor is internal to the Hydraulic Control Unit (HCU). The Brake Torque signal is calculated by the BSCM. The calculation is based on the sum of the hydraulic pressure to the calipers in all four hydraulic circuits. If one of these signals is irrational, the HCU or BSCM are likely faulty.

  1. If the P057B fault is present, perform the circuit fault diagnostics for the BPP Sensor before continuing to step 2.
  2. Verify the BSCM is mounted correctly to the HCU. Next, remove the BSCM and inspect the terminals for signs of damage (pushed out, spread, corroded or dirty terminals).
    • If the BSCM terminals appear damaged, repair the terminals or replace the BSCM in accordance with the Service Information.
    • If the BSCM and terminals appear good, replace the eBooster assembly in accordance with the Service Information.
    NOTE:

    The HCU and BSCM are separate components, but may be required to be replaced as an Integrated Control Unit (ICU) for a period of time on some vehicles. If the BSCM is suspected to be the failure, always check to confirm if the BSCM can be replaced separately. If the HCU is suspected, the entire ICU should be replaced.

PCM IMPLAUSIBLE DATA FAULT (U11BF):  The lost brake signal fault sets when the BSCM detects a fault against the Brake Pedal Pressure Sensor and has no rational signal to send to the PCM.

  1. There should be a circuit fault set in the PCM, BSCM or both. Perform the circuit fault diagnostics for the BPP Sensor before continuing to step 2.
  2. Verify the BSCM is mounted correctly to the HCU. Next, remove the BSCM and inspect the terminals for signs of damage (pushed out, spread, corroded or dirty terminals).
    • If the BSCM terminals appear damaged, repair the terminals or replace the BSCM in accordance with the Service Information.
    • If the BSCM and terminals appear good, replace the HCU in accordance with the Service Information.
    NOTE:

    The HCU and BSCM are separate components, but may be required to be replaced as an Integrated Control Unit (ICU) for a period of time on some vehicles. If the BSCM is suspected to be the failure, always check to confirm if the BSCM can be replaced separately. If the HCU is suspected, the entire ICU should be replaced.

PCM IMPLAUSIBLE DATA FAULT (U0418):  The implausible data fault sets when the BSCM detects a fault against the Master Cylinder Pressure Sensor and has no rational signal to send to the PCM.

  1. Verify the BSCM is mounted correctly to the HCU. Next, remove the BSCM and inspect the terminals for signs of damage (pushed out, spread, corroded or dirty terminals).
    • If the BSCM terminals appear damaged, repair the terminals or replace the BSCM in accordance with the Service Information.
    • If the BSCM and terminals appear good, replace the HCU in accordance with the Service Information.
    NOTE:

    The HCU and BSCM are separate components, but may be required to be replaced as an Integrated Control Unit (ICU) for a period of time on some vehicles. If the BSCM is suspected to be the failure, always check to confirm if the BSCM can be replaced separately. If the HCU is suspected, the entire ICU should be replaced.

PCM LOSS OF COMMUNICATION FAULTS (U0121, U0129):  The U0121 fault sets when the PCM does not receive the Brake Pedal Position Sensor signal message from the BSCM and the U0129 fault sets when the PCM does not receive the Master Cylinder Pressure Sensor signal message. Perform the following diagnostic checks for the Brake System Control Module:

  1. Check for any Service Bulletins, Star On-line Cases, PCM or BSCM flash updates that apply for the DTC or symptom.
  2. Check for any Battery voltage DTCs in the BSCM. Low Battery voltage can cause a DTC.
  3. Verify the vehicle modules are configured correctly. An incorrect configuration can cause a Loss of Communication fault.
  4. Using the wiring information as a guide, check the fuse or fuses that supply power to BSCM. Verify the fuse(s) are not open and has a good connection with the terminals in the PDC
    1. If the fuse(s) are good, continue testing in step 5.
    2. If a fuse is open, check the supply circuit for a short to ground before replacing the fuse.
  5. Disconnect the BSCM harness connector and load test the Battery Supply and Ignition circuits.
    1. A load test is used to determine if a circuit is capable of carrying the amperage needed to perform properly. The 3156 bulb in the load tool illustrated, is a simple but effective method of testing circuit functionality. A 3156 Bulb has approximately 6.0 Ohms of resistance when the bulb is powered and draws approximately 2.0 amps of current. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool and for additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to: CIRCUIT LOAD TESTING PROCEDURES .
    2. To verify that there is no resistance in the circuit being tested, perform a simple voltage drop test across the 3156 bulb of the load test tool. The voltage drop across the bulb should be equal to the voltage reading across the Battery terminals if there is no resistance in the circuit being tested.
      • If either circuit fails the load testing, repair the resistance in the circuit. If the fuse that supplies power to the module is open or damaged
      • If both circuits pass the load test, continue testing in step 6.
  6. Load test the BSCM Ground circuit.
    1. If the ground circuit fails load testing, repair the BSCM chassis ground.
    2. If the ground circuit tests good, continue testing in step 7.
    GC0174957Courtesy of CHRYSLER GROUP, LLC
    GC0174938Courtesy of CHRYSLER GROUP, LLC
  7. Check the voltage on the CAN Bus (+) and CAN Bus (-) circuits at the BSCM. Typically the CAN Bus (+) voltage should be approximately 2.6v and CAN Bus (-) voltage should be approximately 2.4v.
    1. If the voltage readings do not match the values given above, check the suspect circuit for opens or shorts.
      NOTE:

      A short in a Bus circuit would likely cause a Bus Performance fault or affect several modules. If only one module has Loss of Communication faults logged against it due to a wiring issue, it would likely be due to an open in a Bus circuit in the module harness connector or the wiring leading to that module.

    2. If both voltage readings match the values given, the BSCM is likely faulty. Use the wiring information to check all related harness connectors for pushed out, spread, corroded or dirty terminals before condemning the BSCM. To check for an intermittent condition, connect a lab scope to both circuits at the BSCM connector and wiggle test to the wiring harnesses monitoring for a drop in either Bus circuit. If no issues are found, replace the BSCM in accordance with the service information.

The HCU and BSCM are separate components, but may be required to be replaced as an Integrated Control Unit (ICU) for a period of time on some vehicles. If the BSCM is suspected to be the failure, always check to verify if the BSCM can be replaced separately. If the HCU is suspected, the entire ICU should be replaced.

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