C27 Engine for the AD55B Underground Articulated Truck Caterpillar

Use this procedure to troubleshoot any suspect problems with the coolant flow switch.

The coolant flow switch indicates coolant flow in the engine. The Electronic Control Module (ECM) warns the operator of possible engine damage. The switch uses a paddle to close the circuit. When there is enough coolant flow to move the paddle, the switch is closed.

The ECM may modify the operation of the engine in the event of loss of coolant flow. The ECM cannot determine if the switch or the associated components have failed. A problem is present when the ECM detects coolant flow and the engine is not running. A problem is present when there is coolant flow that is determined by other means and the ECM does not detect coolant flow.

Illustration 1	g01707245
Typical example (engine OFF)

Illustration 2	g01707249
Terminal locations at the P1 ECM connector for the coolant flow switch (P1-18) Sensor return (P1-44) Coolant flow switch

Illustration 3	g01155187
Terminal locations at the connector for the coolant flow switch (Terminal 1) Switch signal (Terminal 2) Return

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the ECM connectors J1/P1. Inspect the connector for the coolant flow switch. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

4. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

5. Check the customer connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).

6. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The harness and wiring are OK. Proceed to Test Step 2.

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

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Status of the Coolant Flow on the Caterpillar Electronic Technician (ET)

1. Start Cat ET.

2. Turn the keyswitch to the ON position.

3. Turn the keyswitch to the START position. Start the engine. Allow the engine to run for at least eight seconds so Cat ET can read the flow switch.

4. Observe the reading for coolant flow on Cat ET.

5. Turn the keyswitch to the OFF position.

Expected Result:

Cat ET indicates "FLOW" while the engine is on.

Results:

• OK - Cat ET indicates "FLOW" while the engine is on. The switch is OK.

  Repair: If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - Cat ET does not indicate "FLOW" while the engine is on. Proceed to Test Step 3.

Test Step 3. Create a Short Circuit Condition at the Connector of the Coolant Flow Switch

1. Disconnect the connector of the coolant flow switch.

2. Use a suitable wire jumper and connect terminal 1 to terminal 2.

3. Turn the keyswitch to the ON position.

4. Turn the keyswitch to the START position. Start the engine. Allow the engine to run for at least eight seconds so Cat ET can read the flow switch.

5. Observe the reading for coolant flow on Cat ET.

6. Remove the wire jumper.

7. Observe the reading for coolant flow on Cat ET.

8. Turn the keyswitch to the OFF position.

Expected Result:

Cat ET indicates "FLOW" while the wire jumper is installed. Cat ET indicates "NO FLOW" when the wire jumper is removed.

Results:

• OK - Cat ET indicates "FLOW" while the wire jumper is installed. Cat ET indicates "NO FLOW" when the wire jumper is removed.

  Repair: The wiring between the coolant flow switch and the ECM is OK. Temporarily replace the coolant flow switch. Verify that the problem is no longer present before you permanently install the switch.

  STOP

• Not OK - Cat ET does not indicate "FLOW" while the wire jumper is installed. Cat ET does not indicate "NO FLOW" when the wire jumper is removed. The wiring between the coolant flow switch and the ECM is suspect. Proceed to Test Step 4.

Test Step 4. Check for a Short Circuit in the Wiring Harness

1. Disconnect the connector of the coolant flow switch.

2. Disconnect ECM connector J1/P1 and ECM connector J2/P2.

3. Measure the resistance between P1-44 and every terminal on ECM connector P1 and ECM connector P2.

4. Measure the resistance between P1-44 and the engine ground.

5. Measure the resistance between P1-18 and the engine ground.

Expected Result:

The resistance is greater than 20,000 Ohms.

Results:

• OK - The resistance is greater than 20,000 Ohms. Proceed to Test Step 5.

• Not OK - The resistance is less than 20,000 Ohms. There is a short circuit condition in the harness and/or the connector.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 5. Check for an Open in the Harness

1. Disconnect the connector of the coolant flow switch.

2. Use a wire jumper and connect terminal 1 to terminal 2.

3. Measure the resistance between P1-44 and P1-18.

4. Remove the wire jumper.

Expected Result:

The resistance is less than 5 Ohms.

Results:

• OK - The resistance is less than 5 Ohms. Proceed to Test Step 6.

• Not OK - The resistance is greater than 5 Ohms. There is an open circuit condition in the connectors or the wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 6. Short the Coolant Flow Switch at the ECM Connector

1. Disconnect ECM connector J1/P1.

2. Remove the wire from P1-44 and P1-18 at the ECM connector.

3. Install a jumper wire with Deutsch sockets on each end into P1-44 and P1-18.

4. Reconnect the ECM connector.

5. Turn the keyswitch to the ON position.

6. Turn the keyswitch to the START position. Start the engine. Allow the engine to run for at least eight seconds so Cat ET can read the flow switch.

7. Observe the coolant flow status on Cat ET.

8. Turn the keyswitch to the OFF position.

9. Disconnect ECM connector J1/P1 and remove the wire jumper.

10. Return all wiring to the original configuration.

Expected Result:

Cat ET indicates "FLOW" while the wire jumper is installed.

Results:

• OK - Cat ET indicates "FLOW" while the wire jumper is installed.

  Repair: The ECM is operating correctly. Repair the connectors or wiring and/or replace the connectors or wiring between the ECM and the coolant flow switch.

  STOP

• Not OK - Cat ET does not indicate "FLOW" while the wire jumper is installed. Cat ET does not indicate the correct status of the coolant flow switch.

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

  STOP