26SI Series Alternator – Electronic Control Module (ECM) – Replace

Prior to the replacement of the ECM, ensure that replacement is absolutely necessary. The ECM is seldom the cause of a failure. Always check that power is available to all of the contacts of the ECM that are marked with “+ Battery” and “Key switch”. Continue ONLY if all other attempts to isolate the problem have failed. Always consult your dealership’s technical communicator for possible consultation with Caterpillar. This consultation may greatly reduce the time required for a repair.


  1. Disable the supply voltage to the system. Confirm there is no voltage present at the PL1000T connector.
  1. Disconnect the system harness from the PL1000T.
  1. Remove the PL1000T.
  1. Make sure that the replacement PL1000T is the correct part number.
  1. Install the replacement PL1000T according to the procedures in Special Instruction, REHS2125.
  1. Verify that the ECM operates correctly.