SCREW 0311106 - Caterpillar

Operation Description:The power train ECM applies power to the engine overspeed indicator whenever the engine overspeed test switch is placed in test position. If the engine overspeed indicator is always ON, the harness circuit is shorted to the +battery circuit or the power train ECM has failed.Test Step 1. CHECK THE ENGINE OVERSPEED INDICATOR FOR A SHORT TO THE +BATTERY CIRCUIT
Turn the key start switch to the OFF position.
Disconnect the machine harness from the backup alarm.
Disconnect the machine harness connector J1 and machine harness connector J2 from the power train ECM.
At the machine harness connector, measure the resistance from the signal contact J2-1 (wire 918-OR) to all possible sources of the +battery circuit. Expected Result:Each resistance measurement should be greater than 5000 ohms.Results:
OK - The resistance is greater than 5000 ohms. The machine harness is correct. Proceed to test step 2.
NOT OK - The resistance is less than 5000 ohms.Repair: There is a short in the machine harness. The short is between the backup alarm signal (wire 918-OR) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness. Stop.Test Step 2. CHECK IF THE ABNORMAL CONDITION REMAINS
Inspect the harness connectors and clean the contacts of the harness connectors.
Reconnect all harness connectors.
Turn the disconnect switch and the key start switch to the ON position.
Start the engine. Expected Result:The engine overspeed indicator is always ON regardless of the position of the engine over speed test switch.Results:
YES - The engine overspeed indicator is always ON regardless of the position of the engine over speed test switch. The ECM has failed.Repair: The problem has not been corrected. It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the cause of the diagnostic code is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace". Stop.
NO - The engine overspeed indicator is not always ON regardless of the position of the engine over speed test switch. The problem does not exist at this time. The initial problem was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation. Stop.