C18 Marine Auxiliary 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 is located on the expansion tank.

Illustration 1	g01150024
Components of the coolant level sensor (1) Sensor (2) Sensor probe (brass dowel) (3) Plastic cover

Coolant level sensor (1) 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 (2) that is covered with plastic (3).

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).

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), an event code is activated.

Prior to troubleshooting any problems with the coolant level sensor, use Caterpillar Electronic Technician (ET) to check the installation status for the sensor. The coolant level sensor's configuration parameter must be set to "Installed" in order for the ECM to monitor the signal from the sensor.

The activation of an event 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.

Illustration 2	g01365215
Schematic for coolant level sensor

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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.

Test Step 1. Verify that the "Coolant Level Sensor" Parameter is Programmed Correctly

1. Remove electrical power from the ECM.

2. Connect the Cat ET to the service tool connector.

3. Restore electrical power to the ECM.

4. Establish communication with the ECM.

5. Verify that the "Coolant Level Sensor" parameter is programmed to "Installed".

6. Remove electrical power from the ECM.

Expected Result:

The "Coolant Level Sensor" parameter is programmed to "Installed".

Results:

• OK - The "Coolant Level Sensor" parameter is programmed correctly. Proceed to Test Step 2.

• Not OK - The "Coolant Level Sensor" parameter is not programmed correctly.

  Repair: Program the "Coolant Level Sensor" parameter to "Installed".

  Verify that the repair eliminates the problem.

  STOP

Test Step 2. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.
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   Illustration 3	g01365227
   Location of the coolant level sensor (typical left front engine view) (4) Coolant level sensor

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   Illustration 4	g01365249
   Location of the ECM connectors (typical engine view) (5) J2/P2 connectors

2. Thoroughly inspect the connectors for sensor (4). Also, thoroughly inspect ECM connectors (5). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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   Illustration 5	g01365250
   Terminal locations at the P2 ECM connector for the coolant level sensor (P2-29) Digital sensor supply (P2-49) Coolant level (P2-92) Sensor return

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   Illustration 6	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

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 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 or of pinch points.

Results:

• OK - The harnesses and the wiring appear to be OK. Proceed to Test Step 3.

• 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 3. Check the Supply Voltage at the Sensor Connector

1. Disconnect the coolant level sensor at the sensor connector.

2. Restore electrical power to the ECM.

3. Measure the voltage between terminals A (digital sensor supply) and B (sensor return) 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 4.

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

  Repair: The digital sensor supply voltage is not reaching the sensor. There is a problem in the circuit for the digital sensor supply. Refer to Troubleshooting, "Sensor Supply - Test".

  STOP

Test Step 4. Check the Coolant Level

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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. Remove electrical power from the ECM.

   Note: Allow the engine to cool prior to removal of the cooling system pressure cap.

2. Check the coolant level. Refer to the Operation and Maintenance Manual for the proper procedure to check the coolant level.

Expected Result:

The coolant is at the proper level.

Results:

• OK - The coolant is at the proper level. Proceed to Test Step 5.

• Not OK - The coolant level is low.

  Repair: Add coolant according to the procedure in the Operation and Maintenance Manual.

  There may be a leak in the cooling system. Identify the source of the coolant leak. Repair the leak.

  STOP

Test Step 5. Disconnect the Coolant Level Sensor and Monitor the Status for "Coolant Level"

1. Disconnect the harness connector for the coolant level sensor.

2. Restore electrical power to the ECM.

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

   Note: Wait at least 30 seconds for activation of the status indicator.

4. Remove electrical power from the ECM.

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. There may be a problem with the coolant level sensor. Proceed to Test Step 6.

• Not OK - The status is "OK" when the sensor is disconnected. The problem is between the ECM and the harness connector. There may be a problem with the ECM. Proceed to Test Step 7.

Test Step 6. Short the Signal Wire to Ground and Monitor the Status for "Coolant Level"

1. Remove electrical power from the ECM.

2. Fabricate a jumper wire that is long enough to create a short circuit between two terminals at the coolant level sensor's harness connector. Crimp connector pins to each end of the jumper wire.

3. Install the jumper wire between terminals B (sensor return) and C (sensor signal) on the harness side of the connector for the coolant level sensor.

4. Restore electrical power to the ECM.

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

   Note: Wait at least 30 seconds for activation of the status indicator.

6. Remove electrical power from the ECM.

7. Remove the jumper wire. Connect the harness connector for the coolant level sensor.

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 harness 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. Restore electrical power to the ECM.

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

     Note: Wait at least 30 seconds for activation of the status indicator.

  4. Remove electrical power from the ECM.
  If the status of the "Coolant Level" is "OK", replace the sensor.

  If the status for the coolant level is "LOW", the circuit for the coolant level sensor is OK. There may be an intermittent problem in the harness or in a connector. Fill the cooling system according to the procedure in the Operation and Maintenance Manual. Return the engine to service. If an intermittent electrical problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for troubleshooting information.

  STOP

• Not OK - Shorting the harness does not affect the status on Cat ET. The problem is between the ECM and the harness connector. There may be a problem with the ECM. Proceed to Test Step 7.

Test Step 7. Check the Wiring Harness for an Open Circuit

1. Remove electrical power from the ECM.

2. Disconnect the J2/P2 ECM connector and the connector for the coolant level sensor.

3. Fabricate a jumper wire that is long enough to provide a test circuit between the ECM connector and the sensor connector. Crimp a connector pin to one end of the jumper wire.

4. Install the jumper wire's connector pin into terminal C on the harness side of the connector for the coolant level sensor.

5. Measure the resistance between terminal P2-39 and the loose end of the jumper wire.

   The correct resistance measurement is a short circuit.

Remove the jumper wire. Leave the sensor connector disconnected.

Expected Result:

The measurement indicates that a short circuit exists for the signal wire.

Results:

• OK - The measurement indicated a short circuit. There is not an open circuit in the harness wire for the sensor signal. Proceed to Test Step 8.

• Not OK - The measurement did not indicate a short circuit.

  Repair: There is an open circuit or excessive resistance in the harness or the connectors. Repair the wire and/or the connector, when possible. Replace damaged parts, if necessary.

  STOP

Test Step 8. Check the Harness Wiring for a Short Circuit

1. Remove electrical power from the ECM.

2. Disconnect the J1/P1 and the J2/P2 ECM connectors. Also, disconnect the connector for the coolant level sensor.

3. Measure the resistance between the points that are listed in Table 1.

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

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   Table 1

   Resistance Measurements for the Coolant Level Circuit
   Connector and Terminal	Terminal
   P2-39 (Coolant level)	All of the terminals on the P1 connector
   	All of the other terminals on the P2 connector
   	Engine ground stud

Expected Result:

Each check of the resistance indicates an open circuit.

Results:

• OK - Each check of the resistance indicates an open circuit. There is not a short circuit to another wire in the harness. Proceed to Test Step 9.

• Not OK - At least one check of the resistance does not indicate an open circuit. There is a short to another wire in the harness. The problem may be with a connector.

  Repair: Repair the wire and/or the connector, when possible. Replace damaged parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 9. 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 connector sockets to each end of the jumper wire.

2. Use a wire removal tool to remove the wires from terminal locations P2-92 (sensor return) and P2-49 (coolant level). Install the jumper wire into these terminal locations.

3. Restore electrical power to the ECM.

4. Use Cat ET to monitor the status for "Coolant Level". Use a wire removal tool to remove the jumper wire and check the status again.

   Note: Wait at least 30 seconds for activation of the status indicator.

5. Remove electrical power from the ECM.

Restore all wiring to the original configuration.

Expected Result:

The status is "LOW" when the jumper wire is not connected. The status is "OK" when the jumper wire is connected.

Results:

• OK - The status is "LOW" when the jumper wire is not connected. The status is "OK" when the jumper wire is connected.

  Repair: The ECM is properly reading the switch input. There may be an intermittent problem in the harness or in a connector. If an intermittent electrical problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for troubleshooting information.

  STOP

• Not OK - The status is "LOW" when the jumper wire is connected.

  Repair: The ECM is not reading the switch input. Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP