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

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

The coolant level sensor monitors the engine coolant level in order to warn the operator in the event that the coolant level is low.

The coolant level sensor contains no moving parts. The sensor provides the same function as a switch. The state of the switch is dependent on the capacitance value that is detected at the probe of the sensor. The sensor contains a probe that is covered with plastic.

When the sensor's probe is immersed in coolant, the sensor senses a particular capacitance. The sensor's electronics react by sinking the signal to the sensor return (ground).

The coolant level sensor requires +8 VDC to operate. This voltage is supplied to the sensor by the ECM. The voltage is supplied to terminal ( A) of the sensor. This supply voltage is also used by the coolant temperature sensor and the rack position sensor. A malfunction with the coolant level sensor or the wiring of the sensor can cause problems with these sensors. When the probe is not immersed in coolant, approximately +5 VDC is sourced to the signal wire. When this condition is detected by the Electronic Control Module (ECM), a code is activated.

Illustration 1	g01624976
Schematic for coolant level sensor

Illustration 2	g01635514
(10) +8 VDC (26) Coolant level (35) Analog return

The activation of the following code and/or a warning lamp is probably caused by a low coolant level. The next likely cause is a problem with the wiring harness, a connector, or the sensor. The least likely cause is a problem with the ECM.

Note: In order to log a fault, the sensor must detect low coolant for ten seconds.

Use this procedure in order to troubleshoot any suspect problems with the coolant level sensor(s) or with the wiring circuit.

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.

2. Thoroughly inspect the connector for the coolant level sensor and the P7 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.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Supply Voltage at the Sensor Connector

1. Disconnect the coolant level 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 terminal (A) and terminal (B) at the harness connector for the coolant level 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 3.

• 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 6.

Test Step 3. Disconnect the Coolant Level Sensor and Monitor the Status of "Coolant Level"

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

2. Disconnect the connector for the coolant level sensor.

3. Restore electrical power to the ECM.

4. Monitor the status of "Coolant Level" on Cat ET.

Expected Result:

The status changes from "OK" to "Low" when the sensor is disconnected.

Results:

• OK - The status is "Low" when the sensor is disconnected.

  Repair: The sensor is operating properly.

  STOP

• Not OK - The status is "OK" when the sensor is disconnected. Proceed to Test Step 5.

Test Step 4. Short the Harness and Monitor the Status of "Coolant Level"

1. Install a jumper wire between terminals (B) and (C) on the harness connector for the coolant level sensor.

2. Monitor the status of "Coolant Level" on Cat ET while the jumper wire is installed.

3. Remove the jumper wire.

4. Remove electrical power from the ECM.

Expected Result:

The status changes from "Low" to "OK" when the jumper wire is installed.

Results:

• OK - The status changes from "Low" to "OK" when the jumper wire is installed. The ECM and the wiring to the coolant level sensor are OK.

  Repair: Perform the following procedure:

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  Pressurized System: Hot coolant can cause serious burns. To open the cooling system filler cap, stop the engine and wait until the cooling system components are cool. Loosen the cooling system pressure cap slowly in order to relieve the pressure.

  1. Drain the coolant below the level of the coolant level sensor.

  2. Replace the sensor.

  3. Fill the cooling system according to the procedure in the Operation and Maintenance Manual. Verify that the problem is resolved.

  STOP

• Not OK - Shorting the harness does not affect the status on Cat ET. Proceed to Test Step 5.

Test Step 5. Check the Operation of the ECM

1. Fabricate a jumper wire that is long enough to provide a test circuit across the ECM connector. Crimp the connector sockets to each end of the jumper wire.

2. Remove the P14/26 signal wire from the P14 ECM connector.

3. Install one end of a jumper wire into the location for the signal wire. Ensure that the jumper wire is isolated from other wires and from engine ground.

4. Restore electrical power to the ECM and monitor the status of "Coolant Level" on Cat ET.

5. Connect the other end of the jumper wire to engine ground. Monitor the status of "Coolant Level" on Cat ET.

Expected Result:

The status is "Low" when the jumper wire is not connected to engine ground. The status is "OK" when the jumper wire is connected to engine ground.

Results:

• OK - The status is "Low" when the jumper wire is not connected. The status is "OK" when the jumper wire is connected to engine ground. The ECM is properly reading the sensor input.

  Repair: Repair the signal wire between the ECM and the connector for the sensor.

  STOP

• Not OK - The ECM is not reading the sensor input.

  Repair: Temporarily install a new ECM. Refer to Troubleshooting, "ECM - Replace".If the new ECM works correctly, verify that the problem is resolved.

  STOP

Test Step 6. 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