VENT AIR 3C8503 - Caterpillar

The ECM activates the start relay when the key start switch is in the START position and the direction switch is in the NEUTRAL position. The ECM detects a failure in the circuit for the start relay and the electrical system. If CID 0444 or CID 0168 are present the diagnostic code must be corrected before performing the following procedure "Check the key start switch". See Troubleshooting, "Diagnostic Code List".Test Step 1. CHECK THE KEY START SWITCH IN THE START POSITION.
Make sure that a CID 0444 diagnostic code does not exist. If the diagnostic code exists, correct the failure before proceeding.
Disconnect the ECM from the machine harness.
Turn the disconnect switch to the ON position.
Turn and hold the key start switch in the START position.
At the machine harness connector for the ECM, measure the voltage between contact J2-1 (wire 307-OR(Orange)) and contact J1-70 (ground). Expected Result:The +battery voltage should be present.Results:
YES - The +battery voltage is present. Proceed to Test Step 2.
NO - The +battery voltage is NOT present. The key start switch or the machine harness (wire 307-OR(Orange)) has failed. Check the key start switch and the machine harness.Repair: If necessary, replace the key start switch and/or the machine harness.STOPTest Step 2. CHECK THE KEY START SWITCH IN THE OFF POSITION.
The ECM remains disconnected from the machine harness.
Turn the key start switch to the OFF position.
At the machine harness connector for the ECM, measure the voltage between contact J2-1 (wire 307-OR(Orange)) and contact J1-70 (ground). Expected Result:The +battery voltage should be present.Results:
YES - The +battery voltage is present. The key start switch or the machine harness (wire 307-OR(Orange)) has failed. Check the key start switch and the machine harness.Repair: If necessary, replace the key start switch and/or the machine harness.STOP
NO - The +battery voltage is NOT present. The harness circuit operates correctly. The ECM may have failed.Repair: It is unlikely that the ECM has failed. Perform these test steps again. If the cause is not found, replace the ECM. See Testing and Adjusting, "Electronic Control System (ECM) - Replace".STOP