C18 Industrial Engine Caterpillar

Relay - Test

Usage:

C18 NBB

System Operation Description:

Use this procedure to troubleshoot the electrical system if a problem is suspected with a relay.

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Illustration 1	g01955428
Typical wiring schematic for a relay.

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Illustration 2	g01379309
Terminal locations for a typical relay

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Illustration 3	g01955434
Location of the J1/P1 and the J2/P2 ECM connectors.

Test Step 1. Test the Relay in the De-energized State

Remove the electrical power from the ECM.

Disconnect the relay from the circuit.

Verify the operation of the relay in the de-energized state.
1. Measure continuity across the following terminals of the relay:
  - Terminal 1 to terminal 3
  - Terminal 5 to terminal 2
  - Terminal 1 to terminal 4

Expected Result:

The following results were obtained:

Terminal 1 to terminal 3 indicated a short circuit.
Terminal 5 to terminal 2 indicated some measured resistance.
Terminal 1 to terminal 4 indicated an open circuit.

Results:

OK - Each measurement was correct. Proceed to Test Step 2.
Not OK - A measurement was incorrect.
Repair: Replace the relay and retest the circuit.
STOP

Test Step 2. Test the Relay in the Energized State

Verify the operation of the relay in the energized state.
1. Apply the appropriate voltage across the coil of the relay.
1. Measure continuity across the following terminals of the relay:
  - Terminal 1 to terminal 3
  - Terminal 1 to terminal 4

Expected Result:

The following results were obtained:

Terminal 1 to terminal 3 indicated an open circuit.
Terminal 1 to terminal 4 indicated a short circuit.

Results:

OK - Each measurement was correct. Proceed to Test Step 3.
Not OK - A measurement was incorrect.
Repair: Replace the relay and retest the circuit.
STOP

Test Step 3. Check the Wiring for a Short Circuit

Check the continuity of each wire on the relay connector for a short circuit.
1. Determine the routing of each individual wire from the relay connector. Disconnect any connectors. Check for continuity between the wire and every wire on the connector.
1. Measure continuity between the wire and engine ground.

Expected Result:

Each resistance measurement indicated an open circuit.

Results:

OK - Each resistance measurement indicated an open circuit. Proceed to Test Step 4.
Not OK - One of the resistance measurements indicated a short circuit.
Repair: Repair the wire or replace the wire.
STOP

Test Step 4. Check the Wiring for an Open Circuit

Check the continuity of each wire on the relay connector for an open circuit.
1. Determine the routing of each individual wire from the relay connector. Disconnect any connectors.
1. Create a short between two wires and engine ground.
1. Measure continuity between the other end of the wires.

Expected Result:

Each resistance measurement indicated a short circuit.

Results:

OK - Each resistance measurement indicated a short circuit.
Repair: The circuit appears to be operating correctly. Verify that the correct signal is being sent to the coil of the relay. Verify that the signal from the relay is getting to the driven device.
STOP
Not OK - One of the resistance measurements indicated an open circuit.
Repair: Repair the wire or replace the wire.
STOP

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