An open is a failure of an electrical circuit that results in no flow of electrical current. An open circuit can be 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:
ReferenceFor a complete electrical schematic, refer to Electrical System Schematic for the machine that is being serviced.
TEST FOR AN OPEN CIRCUIT.
- Identify the connectors and the wire numbers of the suspect circuits. Use the Electrical System Schematic of the machine to identify the circuits.
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the component and the ECM from the wiring harness.
- At one of the disconnected harness connections, place a jumper wire from the contact of the suspect wire to frame ground.
- At the other connector of the machine harness, use a multimeter 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.
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.