3512B Marine Auxiliary Engine Caterpillar

The Low/High Idle Switch provides the ability to control engine RPM.

Illustration 1	g00852295

Illustration 2	g00645994

Test Step 1. Check for Connector Damage

1. Turn the ECS to the OFF/RESET position.

2. Check the connectors and wiring for the following problems: damage, corrosion, abrasion and incorrect attachment.

Expected Result:

The connectors and wiring should be free of the following problems: damage, corrosion, abrasion and incorrect attachment.

Results:

• OK - The connectors and wiring are free of problems. Proceed to test step 2.

• Not OK - The connectors and wiring are not free of problems.

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

  Stop.

Test Step 2. Check the Switch on the Caterpillar Electronic Technician (ET).

1. Install the Cat ET to the service tool connector.

2. Turn the ECS to the STOP position. The engine should be OFF.

3. Operate the Low/High Idle Switch. Observe the status of the switch on the Cat ET.

Expected Result:

The parameter for the desired engine speed should change from "1800 RPM" to "LOW IDLE". The parameter for the low idle switch should change from "OFF" to "ON".

Results:

• OK - The engine speed parameter changes from "1800 RPM" to "LOW IDLE". The parameter for the low idle switch changes from "OFF" to "ON".

  Repair: The switch is operating normally. The repair is complete.

  Stop.

• Not OK - The engine speed parameter does not change from "1800 RPM" to "LOW IDLE". The parameter for the low idle switch does not change from "OFF" to "ON". Proceed to test step 3.

Test Step 3. Check the Harness.

1. Construct a jumper wire that can reach from the suspect Electronic Control Module (ECM) to the switch.

2. For the Primary ECM, connect one end of the jumper wire at P1-29. Connect the other end to the switch at pin 2.

3. For the Secondary ECM, connect one end of the jumper wire at P1-8. Connect the other end to the switch at pin 4.

4. Turn the ECS to the STOP position.

5. Change the switch position. Monitor the switch status on the Cat ET .

Expected Result:

The switch status should change.

Results:

• OK - The switch status changes. There is a problem in the wiring between P1-29 and/or P1-8 and the switch.

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

  Stop.

• Not OK - The switch status does not change. There is a problem in the harness and/or the ECM. Proceed to test step 4.

Test Step 4. Check the ECM.

1. Turn the ECS to the OFF/RESET position.

2. Use a suitable piece of wire to short the switch at the junction box.

3. Turn the ECS to the ON position. The engine should be OFF.

4. Monitor the status of the switch on the Cat ET.

Expected Result:

The status of the switch should change with the wire in place.

Results:

• OK - The status of the switch changes.

  Repair: Temporarily connect a new switch. Verify that the new switch solves the problem before you permanently install the new switch.

  Stop.

• Not OK - There is a problem in the harness between the switch and the ECM. Proceed to test step 5.

Test Step 5. Check the Harness.

1. Turn the ECS to the OFF/RESET position.

2. Construct a jumper wire that will reach from the suspect ECM to the switch contact. The Primary ECM connections should be P1-20 to pin 1 at the switch. The Secondary ECM connections should be from P1-8 to pin 4 at the switch.

3. Turn the ECS to the STOP position. The engine should be OFF.

4. Move the switch from the Low Idle position to the High Idle position.

5. Monitor the status of the switch on the Cat ET.

Expected Result:

The status of the switch should change.

Results:

• OK - The status of the switch changes. There is a problem in the wire between the switch contact and the ECM.

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

  Stop.

• Not OK - The status of the switch does not change. Proceed to test step 6.

Test Step 6. Check the Voltage.

1. Place the switch in the Low Idle position.

2. Measure the voltage at the Primary ECM between J1-20 and J1-5.

3. Measure the voltage at the Secondary ECM between J1-8 and J1-5.

Expected Result:

The voltage should be less than 0.9 VDC.

Results:

• OK - The voltage is less than 0.9 VDC.

  Repair: Replace the ECM. Perform the diagnostic procedure Troubleshooting, "Replacing the ECM".

  Stop.

• Not OK - The voltage is greater than 0.9 VDC.

  Repair: If you are troubleshooting an intermittent fault, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  Stop.