336E H Excavator Caterpillar

Relay - Test

Usage:

Machine ECM

The following is a list of Diagnostic Trouble Codes (DTCs) that are associated with the relays related to the Machine ECM.

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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.

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Illustration 1	g03154336
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, UENR2694 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.

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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 less than 5K Ω would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. Proceed to Test Step 5.
Begin Process For FMI 6 Troubleshooting HERE
3. Check The Relay. A. Key start switch and disconnect switch OFF. B. Disconnect the relay from the wiring harness. C. Review the electrical schematic (above) to identify the input and output wires from the coil of the relay. D. Use a multimeter to measure the resistance across the coil of the relay.	The resistance of the coil is less than 50 Ω.	OK - The resistance is less than 50 Ω. Proceed to Test Step 4.. NOT OK - The resistance is greater than 5K Ω. The relay has failed Note: A resistance that is greater than 50 Ω but less than 5K Ω would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. Repair - Replace the relay. Proceed to Test Step 5.
4. Check Machine Harness For A Short To Ground A. Machine harness remains disconnected from relay. B. Turn key start switch and disconnect switch OFF. C. Disconnect harness connectors from ECM (or switch panel). D. At harness connector for ECM, measure resistance between lamp relay contact and all ground contacts.	Each reading greater than 5K Ω.	OK - All machine harness readings are correct. Proceed to Test Step 5. NOT OK - A short circuit exists in machine harness. Repair: The short is between the lamp contact for the relay and the circuit with the low resistance. Repair or replace the machine harness. Note: A resistance that is greater than 5 Ω but less than 5K Ω would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. Proceed to Test Step 5.
5. Check If The Diagnostic Code Remains. A. Turn key switch and disconnect switch ON. B. Clear all diagnostic codes. C. Operate the machine. D. Stop machine and engage parking brake. E. Check if diagnostic code is active.	Diagnostic code is no longer present.	OK - Diagnostic code does not exist at this time. Initial diagnostic code may have been caused by poor electrical connection or short at one of the harness connections. Resume machine operation. STOP NOT OK - Diagnostic trouble code has not been corrected. If the diagnostic code has not been corrected after performing the procedure a second time, the ECM (or Switch Panel) may require replacement. Prior to replacing this component, always contact the Technical Communication at your dealership for possible consultation with Caterpillar. This consultation may greatly effect repair time. Follow the steps in Troubleshooting, "Electronic Control Module (ECM) - Replace" if the ECM needs to be replaced. STOP