LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Fiat >> 2017 >> 124 Spider Classica, Automatic Trans >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Exterior Lights >> (Adaptive Front Lighting System Module - Electrical Diagnostics) >> DTC Troubleshooting >> U0140-00 Lost Communication With Body Control Module (BCM) >> Diagnostic Test
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Test

  1. CHECK FOR PRESENCE OF SHORT CIRCUIT TO BATTERY ON THE CAN H (HS-CAN) LINE 
    1. Measure the voltage between pin F of the diagnostic connector (CAN H line) and body.

      Is a voltage of 12 V measured?

      Yes 

      • Short circuit to battery has occurred on the CAN H line.
      • Move on to  3.

      No 

      • Move on to  2.
  2. CHECK FOR PRESENCE OF SHORT CIRCUIT TO GROUND ON THE CAN H (HS-CAN) LINE 
    1. Measure the voltage between pin E of the diagnostic connector (CAN L line) and ground.

      Is voltage higher than 0 V?

      Yes 

      • Short circuit to ground has occurred on the CAN L line.
      • Move on to  5.

      No 

      • Move on to  8.
  3. CHECK FOR PRESENCE OF SHORT CIRCUIT TO BATTERY ON THE HS-CAN LINE 
    1. Pin F of the diagnostic connector (CAN H line) and body
    2. Pin E of the diagnostic connector (CAN L line) and body

      Is a voltage of 12 V measured between any one of these pins?

      Yes 

      • Short circuit to battery has occurred on the HS-CAN line.
      • Move on to  4.

      No 

      • Move on to  6.
  4. CHECK FOR PRESENCE OF SHORT CIRCUIT TO BATTERY ON THE CAN LINE BETWEEN BODY COMPUTER MODULE AND INSTRUMENT PANEL MODULE 
    1. Go to key-off condition.
    2. Disconnect the negative battery lead.
    3. Disconnect the Body Computer Module.
    4. Connect the negative battery lead.
    5. Measure voltage between pins E and F of the diagnostic connector.

      Is the measured voltage 1.5 - 3.5 V?

      Yes 

      • Move on to  5.

      No 

      • Repair or replace the wiring between Body Computer Module and the rest of the system because the wiring is subject to short circuit to battery.
  5. CHECK FOR PRESENCE OF SHORT CIRCUIT TO BATTERY ON THE CAN LINE BETWEEN ENGINE CONTROL MODULE AND BODY COMPUTER MODULE 
    1. Measure voltage on pin AK and pin AL (connector B) of the Engine Control Module.

      Is the measured voltage 1.5 - 3.5 V?

      Yes 

      • Replace the Body Computer Module because subject to short circuit to battery.
      • If the DTC occurs again, move on to  12.

      No 

      • Repair or replace the wiring between Body Computer Module and the rest of the system because the wiring is subject to short circuit to battery.
  6. CHECK FOR PRESENCE OF OPEN CIRCUIT ON THE HS-CAN LINE 
    1. Pin F of the diagnostic connector (CAN H line) and body
    2. Pin E of the diagnostic connector (CAN L line) and body

      Is the voltage between the terminals the same?

      Yes 

      • Short circuit has occurred between the terminals of the HS-CAN line.
      • Move on to  7.

      No 

      • Check the electric connections again.
      • Replace the Body Computer Module if the DTC occurs again.
  7. CHECK FOR PRESENCE OF FAULT ON THE HS-CAN LINE CIRCUIT 
    1. Pin F of the diagnostic connector (CAN H line) and body
    2. Pin E of the diagnostic connector (CAN L line) and body

      Does the voltage between the pins correspond to 0V?

      Yes 

      • Short circuit to ground has occurred on the CAN H (HS-CAN) line.
      • Move on to  8.

      No 

      • A short circuit between the CAN H and the CAN L (HS-CAN) has occurred.
      • Move on to  10.
  8. CHECK FOR PRESENCE OF SHORT CIRCUIT TO GROUND BETWEEN BODY COMPUTER MODULE AND INSTRUMENT PANEL MODULE 
    1. Go to key-off condition.
    2. Disconnect the negative battery lead.
    3. Disconnect the Body Computer Module.
    4. Pin F of the diagnostic connector and body
    5. Pin E of the diagnostic connector and body

      Is short-circuit present?

      Yes 

      • Repair or replace the wiring between Body Computer Module and the rest of the system because the wiring is subject to short circuit to ground.

      No 

      • Move on to  9.
  9. CHECK FOR THE PRESENCE OF SHORT CIRCUIT TO GROUND ON THE BODY COMPUTER MODULE CAN LINE 
    1. PIN C (connector C) of the Body Computer Module and the body
    2. PIN D (connector C) of the Body Computer Module and the body

      Is short-circuit present?

      Yes 

      • Replace the Body Computer Module because subject to short circuit to ground.
      • If the DTC occurs again, move on to  12.

      No 

      • Repair or replace the wiring between Engine Control Module and the rest of the system because the wiring is subject to short circuit to between the terminals.
  10. CHECK FOR PRESENCE OF SHORT CIRCUIT BETWEEN TERMINALS BETWEEN BODY COMPUTER MODULE AND INSTRUMENT PANEL MODULE 
    1. Go to key-off condition.
    2. Disconnect the negative battery lead.
    3. Disconnect pins C and D (connector C) and pins D and C (connector B) of Body Computer Module.
    4. Connect the negative battery lead.
    5. Go to key-on condition (engine off or on).
    6. Measure voltage on pins F and E of the diagnostic connector.

      Is voltage on pins F and E of the diagnostic connector the same?

      Yes 

      • Repair or replace the wiring between Body Computer Module and the rest of the system because the wiring is subject to short circuit to between the terminals.

      No 

      • Move on to  11.
  11. CHECK FOR PRESENCE OF SHORT CIRCUIT BETWEEN THE BODY COMPUTER MODULE TERMINALS 
    1. Go to key-off condition.
    2. Disconnect the negative battery lead.
    3. Check continuity between pin C and pin D (connector C) of the Body Computer Module.

      Is short-circuit present?

      Yes 

      • Replace the Body Computer Module because subject to short circuit to between the terminals.
      • If the DTC occurs again, move on to  12.

      No 

      • Repair or replace the wiring between Body Computer Module and the rest of the system because the wiring is subject to short circuit to between the terminals.
  12. CHECK THAT THE SELF-ADAPTIVE HEADLIGHT MODULE IS WORKING PROPERLY 
    1. Carry out the Self-Adaptive Headlight Module DTC deletion procedure.
    2. Check whether the DTC is still present.

      Is the DTC still present?

      Yes 

      • Repeat the checks from  1.
      • Replace the Self-Adaptive Headlight Module if the DTC occurs again.

      No 

      • End of diagnosis.
scientia non olet · About LEMON Manuals