FILM-INFORMATION 3226274 - Caterpillar

open circuit is a failure of an electrical circuit. The failure results in no flow of electrical current or reduced flow of electrical current in the circuit.An open circuit can be caused by a break in a circuit wire or by an internal problem in a component. An open circuit can be caused by a poor connection or a failed connection in one of the electrical connectors that is used in a circuit.The following procedure checks for an open or a poor connection in a circuit.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 battery disconnect switch to the OFF position.
Disconnect the harness connector from the component. Disconnect the harness connector for 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, 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: Examine all of the harness connectors that are used in the circuit that was checked. Verify that each connection point is clean, dry, and in good condition. Repair or replace any faulty connectors that are found in the circuit. For more information on how to inspect the harness connectors and what conditions to look for when checking a connector, refer to the Testing and Adjusting, "Electrical Connector - Inspect" section in this manual.Stop.When the resistance of a good circuit is measured between one end of a wire and the other end of the wire, less than 5.0 ohms of resistance is expected. A circuit that is completely open due to a broken wire or no connection in a connector will measure greater than 5000 ohms of resistance.A circuit that is not entirely open may allow some current to pass through. However, limited current will pass that allows the circuit to function. This condition can be caused by a wire that is partially broken, but still is intact enough to allow a small amount of current to pass. Partial breaks in a wire are difficult to diagnose because a resistance measurement may check OK through the section of wire that is still intact. When a partial break is suspected in a wire, the load current through the circuit should be checked to verify that the correct amount of current is present.A resistance measurement that is greater than 5.0 ohms and less than 5000 ohms is due to a poor connection in a circuit connector. The connector contacts may be corroded due to moisture that has entered the connector body. A connector pin or socket may not