3176C, 3406E and 3456 Industrial Engines Troubleshooting – Coolant Level – Test

System Operation Description:

The most likely cause of a coolant level alarm is a low coolant level. The next likely cause of a coolant level alarm is a problem in the circuit. The least likely cause of a coolant level alarm is the engine’s Electronic Control Module (ECM).

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

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 (-Battery).

When the probe is not immersed in coolant, approximately +5 VDC is sourced to the signal wire. When this condition is detected by the ECM, an alarm for low coolant is generated.


Illustration 1 g01411138
Schematic for coolant level sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

 

  1. Remove electrical power from the ECM.


Illustration 2 g01435103
ECM
(1) J1/P1 connectors
(2) J2/P2 connectors

  1. Thoroughly inspect connectors (1) and (2). Also, thoroughly inspect any connections that are associated with the coolant level circuit. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.

Illustration 3 g01435093
J1/P1 ECM connector

(P1-2) Coolant level

(P1-29) Digital sensor return

(P1-35) +8 V digital supply

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

 

  1. Check the allen head screw on each 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.

 

  1. Restore electrical power to the ECM.

Illustration 4 g01159881
Terminal locations at the harness connector for the coolant level sensor

(Terminal A) Digital sensor supply

(Terminal B) Sensor return

(Terminal C) Sensor signal

  1. Measure the voltage between terminals A (+8 VDC) and B (return) at the harness connector for the coolant level sensor.

 

  1. 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 8.

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”.

 

  1. Disconnect the connector for the coolant level sensor.

 

  1. Restore electrical power to the ECM.

 

  1. 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. Proceed to Test Step 4. 
  • 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 (return) and C (signal) on the harness connector for the coolant level sensor.

 

  1. Monitor the status of “Coolant Level” on Cat ET while the jumper wire is installed.

 

  1. Remove the jumper wire.

 

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

     

    1. Replace the sensor.

     

    1. 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 for Opens in the Wiring

 

  1. Remove electrical power from the ECM.

 

  1. Disconnect the J1/P1 ECM connector and the connector for the coolant level sensor.

 

  1. Measure the resistance between the following terminals: 
    • P1-2 (coolant level sensor) to pin C on the connector for the coolant level sensor 

Expected Result:

The resistance indicates a short circuit.

Results:

 

  • OK – The resistance indicates a short circuit. There are no opens in the wiring. Proceed to Test Step 6. 
  • Not OK – The resistance indicates an open circuit. There is an open circuit or excessive resistance in the harness or the connectors.Repair: Repair the circuit.Verify that the repair eliminates the problem.

    STOP

Test Step 6. Check the Wiring for a Short Circuit

Note: Wiggle the harness during the following measurements in order to reveal an intermittent condition.

 

  1. Measure the resistance between the points that are listed in Table 1. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.
    Table 1
    Resistance Measurements for the Circuit for the Coolant Level Sensor
    Connector and Terminal Terminal
    P1-2 (engine coolant level) All of the other terminals on the P1 connector
    All of the terminals on the P2 connector
    Engine ground

Expected Result:

Each check of the resistance indicates an open circuit.

Results:

 

  • OK – Each check of the resistance indicates an open circuit. Proceed to Test Step 7. 
  • Not OK – At least one check of the resistance does not indicate an open circuit. There is a problem in the harness. There may be a problem in a connector.Repair: Repair the wire and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.

    STOP

Test Step 7. Create a Short Circuit at the ECM

 

  1. Remove the signal wire for the coolant level sensor from the P1-2 ECM connector.

 

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

 

  1. Restore electrical power to the ECM and monitor the status of “Coolant Level” on Cat ET.

 

  1. Connect the jumper wire to -Battery. Monitor the status of “Coolant Level” on Cat ET.

Expected Result:

The status is “Low” when the jumper wire is not connected. The status is “OK” when the jumper wire is connected to -Battery.

Results:

 

  • OK – The status is “Low” when the jumper wire is not connected. The status is “OK” when the jumper wire is connected to -Battery. 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 8. Check the 8 Volt Supply Voltage at the ECM

 

  1. Disconnect the J1/P1 ECM connector.

 

  1. 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.

 

  1. Remove the wire from terminal location P1-35 (8 V sensor supply). Install a wire jumper into the socket P1-35.

 

  1. Connect the J1/P1 ECM connector.

 

  1. Restore electrical power to the ECM.

 

  1. Measure the voltage between the wire jumper in P1-35 (8 V sensor supply) and -Battery.

 

  1. Remove electrical power from the ECM.

 

  1. 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: Verify that the return wire does not have an open circuit. If the return wire is OK, repair the supply wire.

    STOP

     

  • Not OK – The voltage measurement is not 8.0 ± 0.4 VDC.Repair: Replace the ECM. Refer to Troubleshooting, “ECM – Replace”.

    STOP

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