Conditions Which Generate This Code:
Schematic of the "Alternator R-terminal"
This diagnostic code is recorded when the system voltage is less than 11 DCV and the engine is running.
Test Step 1. CHECK THE "R-TERMINAL" CIRCUIT FOR A SHORT TO GROUND.
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the J1 harness connector from the ECM.
- Measure the resistance between the "Alternator R-terminal" (wire 403-GN), and all of the contacts that are used in the J1 and J2 harness connectors.
Each resistance measurement is greater than 5 ohms.
- OK - The resistance is greater than 5 ohms. The harness is correct. Proceed to Test Step 2.
- NOT OK - The resistance is less than 5 ohms. There is a short to the wire with the low resistance measurement.
Repair: Replace the wire in the circuit for the "R-Terminal" or repair the circuit.
Test Step 2. CHECK THE ALTERNATOR OF THE MACHINE.
- Disconnect the wire (403-GN) from the alternator.
- Start the engine.
- Measure the "Alternator R-terminal" to verify that there is 11 to 32 V square-wave from 0 to 2 kHz. A steady DC voltage that is equivalent to the voltage of the battery should not be present.
The "Alternator R-terminal" should be an 11 to 32 V square-wave from 0 to 2 kHz.
- OK - The "Alternator R-terminal" is an 11 to 32 V square-wave from 0 to 2 kHz. Proceed to Test Step 3.
- NOT OK - The "Alternator R-terminal" is not an 11 to 32 V square-wave from 0 to 2 kHz.
Repair: Repair the alternator or replace the alternator.
Test Step 3. CHECK IF THE DIAGNOSTIC CODE IS STILL ACTIVE.
- Clean the contacts of the harness connectors.
- Reconnect all harness connectors.
- Turn the key start switch to the ON position and operate the machine.
- Determine if the CID 1251 FMI 04 diagnostic code is present by using the Caterpillar Electronic Technician.
A CID 1251 FMI 04 diagnostic code is present.
- YES - The problem has not been corrected. Failure of the ECM is unlikely.
Repair: If the cause of the problem is not found, contact the Technical Communicator for your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, see Troubleshooting, "Electronic Control Module (ECM) - Replace".
- 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