3512 and 3516 EUI Engines for 784B, 785B, 789B and 793B Off-Highway Trucks ECM Output Circuit (Engine ON Signal) Caterpillar


ECM Output Circuit (Engine ON Signal)
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System Operation Description:

The Electronic Control Module (ECM) signals the Engine Monitoring System (EMS) that the engine is running. The ECM verifies that the engine is running by sensing engine operating conditions such as engine speed and oil pressure. The ECM turns ON the input for the EMS engine ON signal. The input for the EMS engine ON signal is a sinking driver. When the input is turned ON, current flow in the circuit illuminates the lamp for the EMS engine ON signal. The circuit for the EMS engine ON signal can be tested through the use of the diagnostic test on the AVSpare Electronic Technician (ET). The EMS engine ON signal is used to replace the signal from the fuel pressure switch on engines that were equipped with mechanical unit injectors (MUI).

Note: This feature is not present on machines that are equipped with the Vital Information Management System (VIMS).




Illustration 1g00931714

Test Step 1. Check for Connector Damage.

  1. Turn the keyswitch to the OFF position.

  1. Thoroughly inspect the ECM connector J1/P1. Thoroughly inspect the machine connector J2/P2. Inspect the operator monitor panel plug. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

  1. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

  1. Check the ECM connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).

  1. Check the customer connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).

  1. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion or of pinch points.

Results:

  • OK - The connectors and wiring are okay. Proceed to Test Step 2.

  • Not OK - The connectors and/or wiring are not okay.

    Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

    Stop.

Test Step 2. Check the Operation of the High Coolant Temperature Lamp.

  1. Connect the Cat ET to the ECM through the J31 cab service tool connector.

  1. Turn the keyswitch to the ON position. The engine should be off.

  1. Access the diagnostic test on Cat ET.

  1. Activate the override for the EMS engine ON signal.

  1. Monitor the lamp for the EMS engine ON signal.

  1. Deactivate the override for the EMS engine ON signal.

Expected Result:

The lamp for the EMS engine ON signal is not ON before the override is activated. The lamp for the EMS engine ON signal is ON after the override is activated. The lamp for the EMS engine ON signal turns OFF after the override is deactivated.

Results:

  • OK - The lamp for the EMS engine ON signal was ON during the override. The lamp for the EMS engine ON signal turned OFF after the override was deactivated.

    Repair: The lamp for the EMS engine ON signal is operating correctly.

    Stop.

  • Not OK - The lamp for the EMS engine ON signal did not turn ON. Proceed to Test Step 3.

  • Not OK - The lamp for the EMS engine ON signal turned on. The lamp for the EMS engine ON signal did not turn OFF after the override was deactivated. Proceed to Test Step 4.

Test Step 3. Check the Harness for a Short to Ground Condition.

  1. Turn the keyswitch to the OFF position.

  1. Disconnect ECM connector J1/P1.

  1. Disconnect the operator monitor panel plug.

  1. Measure the resistance between the following pins on the ECM connector:

    • P1-35 and P1-23

    • P1-35 and P1-13

    • P1-35 and P1-9

Expected Result:

The resistance is greater than 20,000 Ohms for each measurement.

Results:

  • OK - The resistance is greater than 20,000 Ohms for each measurement. Proceed to Test Step 4.

  • Not OK - The resistance is less than 20,000 Ohms for one of the measurements.

    Repair: The wire 413-BR is shorted to ground through one of the three wires in the engine harness. If the short is to wire 229-BK, wire 413-BR could be shorted to the engine block or to the chassis. If the short is not to wire 229-BK, locate the short in the engine harness or locate the short in the machine harness. Repair the connectors or wiring and/or replace the connectors or wiring.

    Stop.

Test Step 4. Check the Harness for a Short to Battery Condition.

  1. Turn the keyswitch to the OFF position.

  1. Disconnect ECM connector J1/P1.

  1. Disconnect the operator monitor panel plug.

  1. Measure the resistance between the following pins on the ECM connector:

    • P1-35 and P1-70

    • P1-35 and P1-65

    • P1-35 and P1-51

    • P1-35 and P1-37

Expected Result:

The resistance is greater than 20,000 Ohms for each measurement.

Results:

  • OK - The resistance is greater than 20,000 Ohms for each measurement. Proceed to Test Step 5.

  • Not OK - The resistance is less than 20,000 Ohms for one of the measurements.

    Repair: The wire 413-BR is shorted to power through one of the four wires in the engine harness. Locate the short in the engine harness or in the machine harness. Repair the connectors or wiring and/or replace the connectors or wiring.

    Stop.

Test Step 5. Check for an Open in the Harness.

  1. Turn the keyswitch to the OFF position.

  1. Disconnect ECM connector J1/P1.

  1. Disconnect the operator monitor panel plug.

  1. Connect a wire jumper between wire P1-35 (413-BR) and wire P1-2 (201-BK) at the operator monitor panel plug.

  1. Measure the resistance between P1-35 and P1-13 at ECM connector P1.

  1. Remove the wire jumper.

  1. Reconnect all connectors.

Expected Result:

The resistance measures less than 5 Ohms.

Results:

  • OK - The resistance is less than 5 Ohms. Proceed to Test Step 6.

  • Not OK - The resistance is more than 5 Ohms.

    Repair: There is an open or excessive resistance in the wiring and/or in the connectors between ECM connector P1 and the operator monitor panel plug. Repair the connectors or wiring and/or replace the connectors or wiring.

    Stop.

Test Step 6. Check the Voltage to the Operator Monitor Panel Plug for the EMS Engine ON Signal.

  1. Turn the keyswitch to the OFF position.

  1. Turn the keyswitch to the ON position. The engine should be off.

  1. Measure the voltage between P1-35 and P1-13 at ECM connector J1/P1.

  1. Access the diagnostic test on Cat ET.

  1. Activate the override for the EMS engine ON signal.

  1. Measure the voltage between P1-35 and P1-13 at ECM connector J1/P1.

  1. Deactivate the override for the EMS engine ON signal.

  1. Turn the keyswitch to the OFF position.

Expected Result:

The voltage is 7.5 ± 0.5 VDC when the override is OFF. The voltage is 0.5 ± 0.5 VDC when the override is ON.

Results:

  • OK - The voltage was 7.5 ± 0.5 VDC when the override was OFF. The voltage was 0.5 ± 0.5 VDC when the override was ON. There is a problem in the wiring between the ECM and the operator monitor panel plug.

    Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

    Stop.

  • Not OK - The voltage was not 7.5 ± 0.5 VDC when the override was OFF. The voltage was not 0.5 ± 0.5 VDC when the override was ON.

    Repair: The sinking driver on the ECM is not working properly. Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM" before proceeding further.

    Stop.

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