The ECM activates the start relay when the key start switch is in the START position. The ECM detects a failure in the circuit for the start relay and the electrical system. "Check the key start switch". See Troubleshooting, "Diagnostic Code List".
Note: On machines that are equipped with the machine security system (MSS), the output for the start relay goes to the MSS. The MSS will then send an output to the start relay.
Test Step 1. CHECK THE ENGINE START INTERLOCK
Before troubleshooting the key start circuit, ensure that the engine start interlock is not preventing the starter from cranking.
- Use Caterpillar Electronic Technician (Cat® ET) to check that the following inputs are correct for engine starting.
- Security System Status is Disarmed
- Arrest/Seat Status is Arrest Down, and In Seat
- Cab Door Position is Closed
- Engine Speed Value is Zero
- Alternator 'R' Terminal Speed Value is Zero
Expected Result:
The above listed statuses and values are correct.
Results:
- YES - The engine start interlock is NOT preventing the starter from cranking. Proceed to Test Step 2.
- NO - The engine start interlock is preventing the starter from cranking.
Repair: Correct or repair the input indicated.
Note: If the engine speed sensor momentarily fails, the alternator R term becomes the back-up input for engine speed. If the alternator R term displays a value above zero, unplug the alternator connector to attain a zero value. The engine should then be able to start.STOP
Test Step 2. CHECK THE KEY START SWITCH IN THE START POSITION
- Disconnect the ECM from the machine harness.
- 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) and contact J1-13 (wire 203-BK) (ground).
Expected Result:
The +battery voltage should be present.
Results:
- YES - The +battery voltage is present. Proceed to Test Step 3.
- NO - The +battery voltage is NOT present. The key start switch or the machine harness (wire 307-OR) has failed. Check the key start switch and the machine harness.
Repair: If necessary, replace the key start switch and/or the machine harness.
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Test Step 3. 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) and contact J1-13 (wire 203-BK) (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) has failed. Check the key start switch and the machine harness.
Repair: If necessary, replace the key start switch and/or the machine harness.
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- NO - The +battery voltage is NOT present. The harness circuit operates correctly.
Repair: ECM failure is unlikely. Perform these test steps again and check for other causes that may prevent the starter from engaging.
Prior to replacing an ECM, contact your dealer Technical Communicator (TC) for possible consultation with Caterpillar. This consultation may greatly reduce repair time and expense.
If the ECM must be replaced, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".STOP