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

The coolant temperature sensor measures engine coolant temperature. The Electronic Control Module (ECM) uses the information to modify the engine operation for cold operation. The ECM also uses this information to alert the operator of a high coolant temperature.

The following cold start strategy is activated when the coolant temperature is below 60 °C (140 °F).

• Cold mode is deactivated if the engine has been running for five minutes.

• Cold mode is deactivated when the engine speed increases above 1200 rpm.

• The rack position is limited to 5 mm (0.20 inch) during engine start-up (0 - 500 rpm).

The coolant temperature sensor requires +8 VDC to operate. This supply voltage is also used by the coolant level sensor and the rack position sensor. A malfunction with the coolant temperature sensor or the wiring of the sensor can cause problems with these sensors.

Illustration 1	g01625463

Illustration 2	g01635493
(10) +8 VDC (20) Coolant temperature (35) Analog return

Use this procedure to troubleshoot any suspect problems with the circuit for the coolant temperature sensor.

Test Step 1. Inspect the Electrical Connectors and the Wiring Harness

1. Remove electrical power from the ECM.

2. Thoroughly inspect the connector for the coolant temperature sensor and the P12 connector. 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.

  STOP

Test Step 2. Check for Active Open or Short Diagnostic Codes

1. Connect Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Turn the engine control switch to the ON position. The engine should remain off.

3. Check for active diagnostic codes 110-03 or 110-04.

Expected Result:

There are no active diagnostic codes.

Results:

• OK - There are no active diagnostic codes. Proceed to Test Step 3.

• Not OK - The service tool shows an active 110-03 or 110-04 code.

  Repair: Refer to Troubleshooting, "Sensor Signal (Analog, Active) - Test ".

  STOP

Test Step 3. Check the Supply Voltage at the Sensor Connector

1. Disconnect the coolant temperature sensor.

2. Restore electrical power to the ECM.

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Illustration 3	g01356605
Harness connector for the coolant level sensor (A) +8 VDC (B) Return (C) Signal

3. Measure the voltage between terminals (A) and (B) at the harness connector for the coolant temperature sensor.

4. Remove electrical power from the ECM.

Expected Result:

The voltage measurement is +8.0 ± 0.4 VDC.

Results:

• OK - The voltage measurement is +8.0 ± 0.4 VDC. The supply voltage is reaching the sensor. Proceed to Test Step 5.

• Not OK - The voltage measurement is not +8.0 ± 0.4 VDC. The digital sensor supply voltage is not reaching the sensor. Proceed to Test Step 4.

Test Step 4. Check the +8 Volt Supply Voltage at the ECM

1. Disconnect the J14/P14 ECM connector.

2. Fabricate a wire jumper that is long enough to be used to measure the supply voltage at the ECM connector. Crimp a connector socket to one end of the wire.

3. Remove the wire from terminal location P14-10 (+8 V sensor supply). Install a wire jumper into the socket P14-10.

4. Connect the J14/P14 ECM connector.

5. Restore electrical power to the engine ECM.

6. Measure the voltage between the wire jumper in P14-10 (+8 V sensor supply) and engine ground.

7. Remove electrical power from the ECM.

8. Remove the wire jumper and replace all wires.

Expected Result:

The voltage measurement is +8.0 ± 0.4 VDC.

Results:

• OK - The voltage measurement is +8.0 ± 0.4 VDC. The ECM is operating correctly.

  Repair: Repair the wiring harness or replace the wiring harness.

  STOP

• Not OK - The voltage measurement is not +8.0 ± 0.4 VDC.

  Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP

Test Step 5. Check for Signal Voltage at the Sensor

1. Restore electrical power from the ECM.

2. Measure the voltage between J12/B and J12/C.

3. Remove electrical power from the ECM.

Expected Result:

The measurement should be between 0.6 VDC and 3.9 VDC.

Results:

• OK - The voltage is between 0.6 VDC and 3.9 VDC. Proceed to Test Step 6.

• NOT OK - The voltage is not present between J12/B and J12/C.

  Repair: Replace the sensor.

  STOP

Test Step 6. Check For Signal Voltage At the ECM

1. Remove electrical power from the ECM.

2. Remove the wires from P14/35 and P14/20.

3. Restore electrical power to the engine ECM.

4. Measure the voltage between wires P14/35 and P14/20.

5. Remove electrical power from the ECM.

6. Replace all wires.

Expected Result:

The measurement is between 0.6 VDC and 3.9 VDC.

Results:

• OK - The measurement is between 0.6 VDC and 3.9 VDC.

  Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP

• NOT OK - The measurement is not between 0.6 VDC and 3.9 VDC.

  Repair: Repair the wiring harness or replace the wiring harness.

  STOP