CARRIER 1T0226 - Caterpillar

Machine ECM
The following is a list of Diagnostic Trouble Codes (DTCs) that are associated with the relays related to the Machine ECM.
Table 1
Machine ECM (MID 299)
DTC Code Description System Response
781-3 Lighting Relay : Voltage Above Normal Related lighting system will be ON continuously.
781-6 Lighting Relay : Current Above Normal Related lighting system will be ON continuously.
2912-3 Front Wiper Speed Control Relay : Voltage Above Normal Wiper system will not function.
2912-6 Front Wiper Speed Control Relay : Current Above Normal Wiper system will not function.
3634-3 Boom Light Relay : Voltage Above Normal Related lighting system will be ON continuously.
3634-6 Boom Light Relay : Current Above Normal Related lighting system will be ON continuously. Possible Causes for an FMI 3 Diagnostic code are:
The ground wire is open.
The signal wire is permanently open.
The signal wire is permanently closed.
The indicator lamp has failed.
The Switch Panel has failed. This situation is unlikely.Possible Causes for an FMI 6 Diagnostic code are:
A short to ground exists.
The indicator lamp has failed.
The Switch Panel has failed. This situation is unlikely.
Illustration 1 g03453634
Schematic of the relay circuits associated with the Switch Panel
Note: The diagram above is a simplified schematics of the Machine ECM and the Switch Panel connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest revision of Electrical Schematic, UENR2487 (374F) or Electrical Schematic, UENR2489 (390F) for the complete schematic.Diagnostic Trouble Code Procedure
Note: Prior to beginning this procedure, inspect the harness connectors that are involved in this circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure, and in good condition. Check the wiring harness for pinch points or abrasions. Look for and repair areas that indicate wires are exposed. If a problem with a connection is found, correct the problem and verify that the diagnostic code is active before performing a troubleshooting procedure.
Table 2
Troubleshooting Test Steps Values Results
1. Identify Active FMI Code Associated With Relay Circuit
Code present. FMI 3 diagnostic code, proceed to Test Step 2.
FMI 6 diagnostic code, proceed to Test Step 3.
Begin Process For FMI 3 Troubleshooting HERE
2. Check The Machine Harness For A Short
A. Turn key start switch and disconnect switch OFF.
B. Disconnect harness connection at relay.
C. If relay connected to ECM, disconnect J1 and J2 connectors from ECM. If relay connected to Switch Panel, disconnect all switch panel connectors.
D. Measure resistance of relay signal contact to all J1 and J2 connectors, if relay is wired directly to Machine ECM. If relay is wired directly to switch panel, measure resistance of relay contact to all switch panel connectors.
Each reading greater than 5K Ω. OK - All resistance measurements are greater than 5K Ω.
Proceed to Test Step 5.
NOT OK - One or more readings are less than 5 Ω.
Repair - A short exists between the signal contact and the circuit with the low resistance. Repair or replace the machine harness.
Note: A resistance that is greater than 5 Ω but