MAST A.-STAT. 0331954 - Caterpillar

Illustration 1 g02612741
Scraper Engine Start circuitIn order to enable the two Scraper Engine Start switches, the tractor key switch must be in the ON position. Then, the Tractor Main Relay is energized and sends power to both start switches. When either switch is held in the START position, the Scraper Engine ECM will receive +Battery power from the switch at connector contact J2-1. After one second, the ECM will check to see that the Direction switch is in the NEUTRAL position. The ECM will then energize the Start Relay signal out of contact J2-7, to energize the Start Relay. The Start Relay will send +Battery to the starting motor. The ECM software will detect a failure in the circuit for the Start Relay and the electrical system. A start signal from the cab start switch is routed through the rear switch and then to the ECM.Note: If a CID 0444 or a CID 0168 diagnostic code is active, the diagnostic code must be corrected before performing the following procedure. See Testing and Adjusting, "Troubleshooting Service Codes" for diagnostic code procedures.When the cab start switch or the rear start switch cannot crank the engine, the switches are not receiving power from the Tractor Main Relay. Investigate the Tractor Main Relay for correct operation. If the Tractor Main Relay is working correctly, check the machine harness for an open circuit in wire 128-PK.If the cab start switch cranks the scraper engine, but the rear switch does not: The rear switch is faulty, or is not receiving power from the scraper main relay.Perform the following test steps whenever the cab start switch does not crank the rear engine, but the rear switch does.Test Step 1. CHECK REAR SWITCHThe tractor key switch is in the OFF position.
Disconnect the machine harness connector from the rear start switch.
At the machine harness connector for the rear start switch, place a jumper between connector contact B (wire R737-YL) and contact B (wire 307-OR).
Turn the tractor key switch to the ON position.
Hold the cab start switch in the START position.Expected Result:The scraper engine cranks.Results:
YES - The scraper engine cranks.Repair: The rear start switch is faulty. Replace the rear start switch.STOP
NO - The scraper engine did not crank. Either the cab switch or the machine harness is faulty. Proceed to Test Step 2.Test Step 2. CHECK FRONT SWITCH AND HARNESSThe tractor key switch is in the OFF position.The rear start switch is connected to the machine harness.
At the cab start switch, disconnect the switch from the machine harness.
At the disconnected machine harness connector for the cab switch, place a jumper wire between contact 2 (wire 128-PK) and contact 3 (wire R737-YL).
Before the next step, be prepared for the scraper engine to crank. Ensure that all personal are clear before performing the next step.
Turn the tractor key switch to the ON position.Expected Result:The scraper engine cranks.Results:
YES - The scraper engine cranks. The start switch in the cab is faulty.Repair: Replace the cab start switch.STOP
NO - The scraper engine does not