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Home >> Fiat >> 2019 >> 124 Spider Classica, Automatic Trans >> Repair and Diagnosis >> Steering >> Steering Control Systems >> (Electronic Power Steering (EPS) Module - Electrical Diagnostics) >> DTC Troubleshooting >> U0121-00 Lost Communication With Anti-Lock Brake System (Abs) Control Module >> Diagnostic Test

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.
      • Go to  3.

      No 

      • Go 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.
      • Go to  7.

      No 

      • Go to  5.
  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.
      • Go to  4.

      No 

      • Go to  5.
  4. CHECK FOR PRESENCE OF SHORT CIRCUIT TO BATTERY OF THE ANTI-LOCK BRAKE SYSTEM (ABS) MODULE 
    1. Go to key-off condition.
    2. Disconnect the negative battery lead.
    3. Disconnect the Anti-lock Brake System (ABS) Module connector.
    4. Connect the negative battery lead.
    5. Go to key-on condition (engine off).
    6. Measure voltage on pins F and E of the diagnostic connector.

      Is the measured voltage 1.5 - 3.5 V?

      Yes 

      No 

      • Repair or replace the wiring between ABS Module and the rest of the system because the wiring is subject to short circuit to battery.
  5. 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.
      • Go to  6.

      No 

  6. 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.
      • Go to  7.

      No 

      • A short circuit between the CAN H and the CAN L (HS-CAN) has occurred.
      • Go to  8.
  7. CHECK FOR PRESENCE OF SHORT CIRCUIT TO GROUND ON THE ANTI-LOCK BRAKE SYSTEM (ABS) MODULE CAN LINE 
    1. Disconnect the Anti-lock Brake System (ABS) Module connector.
    2. pin C of Anti-lock Brake System (ABS) Module (wiring side) and body
    3. pin D of Anti-lock Brake System (ABS) Module (wiring side) and body

      Is short-circuit present?

      Yes 

      • Repair or replace the wiring between Anti-lock Brake System (ABS) Module and the rest of the system because the wiring is subject to short circuit to ground.

      No 

  8. CHECK FOR PRESENCE OF SHORT CIRCUIT BETWEEN THE ANTI-LOCK BRAKE SYSTEM (ABS) MODULE TERMINALS 
    1. Disconnect the ABS Module connector.
    2. Disconnect the negative battery lead.
    3. Check continuity between pin C and pin D (wiring side) of the ABS Module.

      Is short-circuit present?

      Yes 

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

      No 

  9. CHECK THAT THE ELECTRIC POWER STEERING (EPS) MODULE IS WORKING PROPERLY 
    1. Carry out the Electric Power Steering (EPS) Module error deletion procedure.
    2. Check whether the error is still present.

      Is the error still present?

      Yes 

      • Repeat the checks from Step 1.
      • Replace the Electric Power Steering (EPS) Module in accordance with the Service Information. Refer to GEAR, REMOVAL AND INSTALLATION .

      No 

      • End of diagnosis.
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