Wiring Harness (Short Circuit) - Test
A short circuit is a failure of an electrical circuit that results in undesired electrical current. Usually, a short circuit is a bypass of the circuit across a load. For example, a short across the wires in a circuit for a lamp produces too much current in the wires but no current is felt at the lamp. The lamp is shorted out. The resistance in a normal circuit can vary, but the resistance between a particular circuit and other unrelated circuits is always greater than 5000 ohms. The following procedure explains the test for a short circuit:
Reference: For a complete electrical schematic, refer to Electrical System Schematic for the genset that is being serviced.
TEST FOR A SHORT CIRCUIT.
- Identify the connectors and the wire numbers of the suspect circuits. Use the Electrical System Schematic of the genset 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 the harness connector for the ECM, place one of the multimeter probes on the contact of the suspect wire.
- Use the other multimeter probe to check the resistance across all other contacts in the connector(s) of the ECM and frame ground.
Expected Result: The resistance is greater than 5000 ohms for all the measurements.
OK - The resistance is greater than 5000 ohms for all of the measurements. The harness circuits are correct.
Stop.
NOT OK - The resistance is less than 5000 ohms. There is a short in the harness of the generator set. The short is between the suspect wire and the wire with the lowest resistance measurement.
Repair: Repair the harness of the generator set or replace the harness of the generator set.
Stop.
Caterpillar Information System:
EMCP4.1/EMCP4.2 Diagnostic Capabilities
EMCP4.1/EMCP4.2 Diagnostic Trouble Code List
EMCP4.1/EMCP4.2 Engine Cooldown Warning
EMCP4.1/EMCP4.2 Engine Overcrank Warning
EMCP4.1/EMCP4.2 Engine Overspeed Warning
EMCP4.1/EMCP4.2 Engine Speed Warning
EMCP4.1/EMCP4.2 Engine Underspeed Warning
EMCP4.1/EMCP4.2 Generator Control Not in Automatic Warning
EMCP4.1/EMCP4.2 Generator Output Sensing Circuit Fault
EMCP4.1/EMCP4.2 Generator Overcurrent Warning
EMCP4.1/EMCP4.2 Generator Overfrequency Warning
EMCP4.1/EMCP4.2 Generator Overvoltage Warning
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