3412, 3412C, and 3412E Generator Set Engines Caterpillar

The idle/rated switch allows the operator to maintain the engine at low idle. This is allowed after sufficient oil pressure has been obtained. Idle mode is activated by an open circuit at the idle/rated Input to the ECM. Rated mode is selected by connecting the idle/rated input to ground. The idle/rated input should measure approximately 24 VDC at P14-17. The switch input is open at this time. When the switch is closed, the voltage will be less than .5 VDC.

Use this procedure to troubleshoot the electrical system if a problem is suspected with the circuit for the idle/rated switch.

Illustration 1	g01627553

Illustration 2	g01635735
(17) Idle/Rated switch

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.

2. Thoroughly inspect the P17/J17 connector for the idle/rated switch. Inspect the ECM connector J14/P14. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the coolant level sensor.

4. Check the allen head screw on the ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

Expected Result:

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

Results:

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

• Not OK - There is a problem with the connectors and/or the wiring.

  Repair: Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Switch Status with an Electronic Service Tool

1. Turn the engine control switch to the OFF position.

2. Connect Caterpillar Electronic Technician (ET) to the service tool connector.

3. Turn the engine control switch to the ON position. The engine should remain in the OFF position.

4. Observe the status of the idle/rated switch on Cat ET. Operate the idle/rated switch and observe the status.

Expected Result:

The status of the idle/rated switch should read "Idle" when the switch is open. The status of the idle/rated switch should read "Rated" when the switch is closed.

Results:

• OK -

  Repair: The idle/rated switch is functioning properly. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• NOT OK - The status of the idle/rated switch does not read "Idle" when the switch is open. The status of the idle/rated switch does not read "Rated" when the switch is closed. Proceed to Test Step 3.

Test Step 3. Short the Switch Inputs at the Switch

1. Turn the engine control switch to the OFF position.

2. Disconnect the wires from the idle/rated switch.

3. Turn the engine control switch to the ON position. The engine should remain in the OFF position.

4. Connect and disconnect the wires for the idle/rated switch. Observe the status on Cat ET.

Expected Result:

The status of the idle/rated switch reads "Idle" when the wires are disconnected. The status of the idle/rated switch reads "Rated" when the wires are shorted.

Results:

• OK - The status of the Idle/Rated Switch reads "Idle" when the wires are disconnected. The status of the idle/rated switch reads "Rated" when the wires are shorted.

  Repair: Check the switch terminals for corrosion or damage. If there is no corrosion or damage, replace the idle/rated switch.

  STOP

• NOT OK - The status of the idle/rated switch does not read "Idle" when the wires are disconnected. The status of the idle/rated switch does not read "Rated" when the wires are shorted. Proceed to Test Step 4.

Test Step 4. Check for Engine Ground at the Switch

1. Disconnect the -Battery wire at the idle/rated switch.

2. Measure the resistance between the- battery wire and engine ground.

Expected Result:

The resistance measures less than 10 Ohms.

Results:

• OK - The resistance measures less than 10 Ohms. Proceed to Test Step 5.

• NOT OK - The resistance measures more than 10 Ohms.

  Repair: There is an open in the harness. Repair the harness or replace the harness.

  STOP

Test Step 5. Check the Resistance through the Harness

1. Disconnect the wires from the idle/rated switch. Connect the two wires together without the switch.

2. Disconnect J14/P14.

3. Measure the resistance between P14-17 and P14-21.

Expected Result:

The resistance measures less than 10 Ohms.

Results:

• OK - The resistance measures less than 10 Ohms. Proceed to Test Step 6.

• NOT OK - The resistance measures more than 10 Ohms.

  Repair: There is a open in the harness. Repair the harness or replace the harness.

  STOP

Test Step 6. Check For Shorts In The Harness.

1. Disconnect the wires for the idle/rated switch.

   Note: The wires should be isolated from each other. The wires should not be allowed to come in contact with the engine ground.

2. Disconnect J14/P14.

3. Measure the resistance betweenP14-17 and P14-21.

Expected Result:

The resistance measures more than 20,000 Ohms.

Results:

• OK - The resistance measures more than 20,000 Ohms. Proceed to Test Step 7.

• NOT OK - The resistance measures less than 20,000 Ohms.

  Repair: There is a short in the harness. Repair the harness or replace the harness.

  STOP

Test Step 7. Short the Switch Input at the ECM

1. Turn the engine control switch to the OFFposition.

2. Remove wire C418-WH from connector P14-17.

3. Turn the engine control switch to the ON position. Observe the status on Cat ET.

4. Turn the engine control switch to the OFF position. Observe the status on the Cat ET.

5. Insert a wire with a "Deutsch" socket terminal into P14-17. Connect the other end to engine ground.

6. Turn the engine control switch to the ON position. Observe the status on Cat ET.

7. Turn the engine control switch to the OFF position. Observe the status on Cat ET.

Expected Result:

The status of the idle/rated switch reads "Idle" when the wire is disconnected. The status of the idle/rated switch reads "Rated" when the wire is connected.

Results:

• OK - The status of the idle/rated switch reads "Idle" when the wire is disconnected. The status of the idle/rated switch reads "Rated" when the wire is connected.

  Repair: The harness is faulty. Repair the harness or replace the harness.

  STOP

• NOT OK - The ECM is not reading the signal. Replace the ECM. STOP