CT660 CX31 and CX31 HT On Highway Truck Power Train Electronic Control System Caterpillar

An open is a failure of an electrical circuit that results in no flow of electrical current. An open circuit is usually caused by failed electrical wires or a poor connection of electrical connectors. If an electrical wire or a connection is broken, the flow of electrical current through the circuit is interrupted. A normally closed circuit will have less than 5 ohms of resistance. The following procedure explains the test for an open circuit:

Reference: For a complete electrical schematic, refer to Electrical System Schematic for the machine that is being serviced.

TEST FOR AN OPEN CIRCUIT.

1. Identify the connectors and the wire numbers of the suspect circuits. Use the Electrical System Schematic of the machine to identify the circuits.

2. Turn the key start switch and the disconnect switch to the OFF position.

3. Disconnect the component and the ECU from the wiring harness.

4. At one of the disconnected harness connections, place a jumper wire from the contact of the suspect wire to frame ground.

5. At the other connector of the machine harness, use the multimeter probes to measure the resistance from the contact of the suspect wire to frame ground.

   Expected Result: The resistance is less than 5 ohms.

   OK - The resistance is less than 5 ohms. The harness circuit is correct.

   Stop.

   NOT OK - The resistance is greater than 5000 ohms. There is an open in the machine harness.

   Repair: Repair the machine harness or replace the machine harness.

   Stop.