3126B Petroleum Engine Caterpillar

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

The engine coolant level sensor provides a means of monitoring the engine coolant level in order to warn the operator in the event that the coolant level is low. The engine coolant level sensor is usually located in the top tank of the radiator. The sensor should be immersed in coolant at all times.

When the sensor is immersed in coolant, an internal switch is closed. When the internal switch closes, the signal for the engine coolant level is grounded through the sensor return. The Electronic Control Module (ECM) detects the grounded signal on the input for the engine coolant level. If the signal is not present, an event code is generated.

Verify that the coolant level has been programmed to "Installed" on the configuration screen on the Caterpillar Electronic Technician (ET). If the coolant level is not programmed, Cat ET will display "Not Installed" for the parameter.

Illustration 1	g00806192
Schematic for coolant level sensor

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The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere.

Test Step 1. 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. Stop the engine. Allow the engine to cool.

2. Check the coolant level. Refer to the engine's Operation and Maintenance Manual for the proper procedure.

Expected Result:

The coolant level is low.

Results:

• OK - The coolant level is low.

  Repair: Add coolant according to the procedure in the Operation and Maintenance Manual. Identify the source of the coolant leak and fix the problem. Verify that the original problem is resolved.

  STOP

• Not OK - The coolant is at the proper level. Proceed to Test Step 2.

Test Step 2. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.

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Illustration 2	g01146374
Left side engine view (typical example) (1) J1/P1 ECM connector

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Illustration 3	g01146383
Left side engine view (typical example) (2) P61 Customer connector

2. Thoroughly inspect connectors (1) and (2). Inspect the J800/P800 connectors for the engine coolant level sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 4	g01128767
P1 terminals that are associated with the engine coolant level sensor (P1-3) Digital return (P1-4) +8 V Digital supply (P1-46) Engine coolant level

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Illustration 5	g01119200
J61 and P61 terminals that are associated with the engine coolant level sensor (8) +8 V Digital supply (15) Digital return (36) Engine coolant level

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector, the customer connector, and the sensor connector that is associated with the circuit for the engine coolant level sensor.

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

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 3.

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

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly connected. Verify that the original problem is resolved.

  STOP

Test Step 3. Short the Harness and Monitor the Status of the "Coolant Level"

1. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Disconnect the J800/P800 connectors for the engine coolant level sensor.

3. Install a jumper wire between P800-B (digital return) and P800-C (coolant level sensor).

4. Turn the keyswitch to the ON position.

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

6. Turn the keyswitch to the OFF position.

7. Remove the jumper wire.

8. Connect the J800/P800 connectors.

Expected Result:

The status of the "Coolant Level" is "OK" when the jumper wire is installed.

Results:

• OK - The status of the "Coolant Level" is "OK" when the jumper wire is installed. The ECM, the signal wire, and the return wire are OK. Proceed to Test Step 4.

• Not OK - The status of the "Coolant Level" is not "OK" when the jumper wire is installed. Proceed to Test Step 5.

Test Step 4. Check the Supply Voltage at the Sensor Connector

1. Disconnect the J800/P800 connectors.

2. Turn the keyswitch to the ON position.

3. Measure the voltage between terminals P800-A (+8 V digital supply) and P800-B (digital return) at the harness connector for the engine coolant level sensor.

4. Turn the keyswitch to the OFF position.

Expected Result:

The voltage between terminals A (+8 V digital supply) and B (digital return) is 8.0 ± 0.4 VDC.

Results:

• OK - The supply voltage is reaching the sensor.

  Repair: Replace the engine coolant level sensor. Verify that the original problem is resolved.

  STOP

• Not OK - The supply voltage is not reaching the sensor.

  Repair: Refer to Troubleshooting, "Digital Sensor Supply Circuit - Test" for the appropriate troubleshooting procedure.

  STOP

Test Step 5. Create a Short Circuit at the ECM P1 Connector

1. Remove terminals P1-3 and P1-46. Install a jumper wire into open terminals P1-3 and P1-46.

2. Turn the keyswitch to the ON position and monitor the status of "Coolant Level" on Cat ET while the jumper wire is installed.

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

4. Turn the keyswitch to the OFF position.

Expected Result:

The status of the switch is "OK" when the jumper wire is connected. The status of the switch is "Low" when the jumper wire is not connected.

Results:

• OK - The status of the switch is "OK" when the jumper wire is connected. The status of the switch is "Low" when the jumper wire is not connected. The ECM is properly reading the switch input. However, the ECM did not detect the jumper wire at the sensor connector. There is a problem with the wiring. There may be a problem with a connector.

  Repair: Repair the wiring and/or the connector. Replace parts, if necessary. Verify that the original problem is resolved.

  STOP

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

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the original problem is resolved.

  STOP