26SI Series Alternator – MID 122 – CID 1251 – FMI 03

Conditions Which Generate This Code:

The Product Link module tracks the machine operating hours for reporting to the office. The Alternator R-Terminal signal is used to detect when the machine is operating. If the input continually receives a voltage signal that is above normal, then machine operation cannot be detected. If the input continually receives a voltage signal that is above normal, the reported Service Meter Hours (SMU) would be inaccurate.

Test Step 1. CHECK THE R-TERMINAL CABLING FOR SHORT TO BATTERY.

  1. Disconnect the Product Link cable (P1) from the Product Link module.
  1. Measure the resistance from the Alternator R-terminal input J1-4 (403MC9-GN-18 to battery (J1-1).

Expected Result:

The resistance should be greater than 5000 ohms.

Results:

  • OK – The Product Link harness is likely correct. Proceed to Test Step 2.

  • NOT OK – The Product Link cable has a probable short to battery.

    Repair: Repair the cable and verify that the fault has been removed.

    STOP

Test Step 2. CHECK THE PRODUCT LINK HARNESS FOR A SHORT TO A VOLTAGE SOURCE.

  1. Disconnect the Product Link cable (P1) from the Product Link module.
  1. Start the engine.
  1. Measure the Alternator R-Terminal input (J1-4) to verify that there is an 11 VDC to 32 VDC square-wave from 0 kHz to 2 kHz. Also, a steady DC voltage equivalent to the battery should be present.

Expected Result:

The Alternator R-Terminal input does not measure at a steady DC voltage equivalent to the battery voltage.

Results:

  • OK – The signal is an 11 VDC to 32 VDC square-wave from 0kHz to 2 kHz or a steady DC voltage equivalent to the battery present. The Product Link harness is likely not faulty. Proceed to Test Step 3.

  • NOT OK – The Product Link cable has a possible short to a DC voltage source other than battery voltage.

    Repair: Repair the cable and verify that the fault has been removed.

    STOP

Test Step 3. CHECK THE MACHINE ALTERNATOR.

  1. Disconnect the Product Link machine cable from the alternator.
  1. Start the engine.
  1. Measure the Alternator R-Terminal to verify that there is 11 VDC to 32 VDC square-wave from 0 kHz to 2 kHz. There should not be a steady DC voltage equivalent to the battery present.

Expected Result:

The alternator R-Terminal should be an 11 VDC to 32 VDC square-wave from 0 kHz to 2 kHz.

Results:

  • OK – The alternator R-Terminal is an 11 VDC to 32 VDC square-wave from 0 kHz to 2 kHz. Proceed to Test Step 4.

  • NOT OK – The alternator R-Terminal is not an 11 VDC to 32 VDC square-wave from 0 kHz to 2 kHz.

    Repair: Repair the alternator or replace the alternator.

    STOP

Test Step 4. CHECK IF THE DIAGNOSTIC CODE IS STILL ACTIVE.

  1. Clean the contacts of the harness connectors.
  1. Reconnect all harness connectors.
  1. Turn the key start switch to the ON position and operate the machine.
  1. Determine if “CID 1251 FMI 03” diagnostic code is present by using the Caterpillar Electronic Technician (Cat ET).

Expected Result:

A “CID 1251 FMI 03” diagnostic code is present.

Results:

  • YES – The problem has not been corrected. It is unlikely that the ECM is faulty.

    Repair: Perform this diagnostic test procedure again. If the cause of the diagnostic code is not found, replace the Product Link ECM. Before replacing the Product Link, contact your Caterpillar Technical Communicator. Refer to Systems Operation, Troubleshooting, Testing and Adjusting, “Electronic Control Module (ECM) – Replace”.

    STOP

  • NO – The diagnostic code is NOT present. The problem does not exist at this time. The initial problem was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.STOP
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