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Coolant flow switch (1) Flow switch assembly (2) PaddleThe coolant flow switch is a normally open switch. The contacts of flow switch assembly (1) close as coolant flow from the engine flows across paddle (2) of the switch. The Electronic Control Module (ECM) monitors the status of the coolant flow switch during engine operation. If the ECM detects a loss of coolant flow in the engine during operation, a signal will be sent in order to alert the operator of the condition.The status of the "Engine Coolant Flow" can be monitored using Cat® Electronic Technician (ET) in order to determine the state of the coolant flow switch.
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Schematic for the coolant flow switchTest Step 1. Verify that the Coolant Level is Correct
Ensure that the coolant level for the engine is correct. Refer to Operation and Maintenance Manual, "Cooling System Coolant Level - Check" for more information.Expected Result:The coolant level is OK.Results:
OK - The coolant level is OK. Proceed to Test Step 2.
Not OK - The coolant level is low.Repair: Diagnose the reason for a low coolant level.Refer to Systems Operation/Testing and Adjusting, "Cooling System" for more information.Verify that the repair eliminates the problem.STOPTest Step 2. Inspect the Electrical Connectors and the Wiring
Remove electrical power from the engine ECM.
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Typical left side engine view (3) J1/P1 ECM connectors
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Typical right side engine view (4) Coolant flow switch
Thoroughly inspect connectors (3) and the connectors for switch (4) . Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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Terminal locations at the P1 ECM connector for the coolant flow switch (P1-45) Coolant flow switch
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Terminal locations at the connector for the coolant flow switch (Terminal 1) Switch signal (Terminal 2) Return
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.Expected Result:All connectors, pins, and sockets are inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points. All connections and grounds are tight and free of corrosion.Results:
OK - The harness and wiring are OK. Proceed to Test Step 3.
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 coupled.Verify that the repair eliminates the problem.STOPTest Step 3. Use Cat ET to Monitor the Switch Status
Connect Cat ET to the service tool connector.
Restore electrical power to the engine ECM.
Observe the status for "Engine Coolant Flow" on the Cat ET.
Turn the keyswitch to the START position. Start the engine.
Again, observe the status for "Engine Coolant Flow" on the Cat ET.
Turn the keyswitch to the OFF position.Expected Result:Cat ET indicates "NO FLOW" while the engine is not running. Cat ET indicates "FLOW" while the engine is running.Results:
OK - Cat ET indicates "NO FLOW" while the engine is not running. Cat ET indicates "FLOW" while the engine is running.Repair: The switch is operating correctly at this time. There may be an intermittent problem with the switch or the switch circuit. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - Cat ET does not indicate "NO FLOW" while the engine is not running. Cat ET does not indicate "FLOW" while the engine is running. Cat ET does not indicate the correct status for the coolant flow switch. Proceed to test step 4.Test Step 4. Create a Short at the Connector for the Coolant Flow Switch
Disconnect the connector for the coolant flow switch.
Fabricate a jumper wire that is long enough to create a short at the harness connector for the coolant flow switch. Crimp connector pins to each end of the jumper wire.
Install the jumper wire to the terminals of the harness connector of the coolant level switch.
Turn the keyswitch to the ON position.
Observe the status of "Engine Coolant Flow" on Cat ET.
Turn the keyswitch to the OFF position. Restore the wiring to the original configuration.Expected Result:The status indicates "FLOW" with the jumper wire in place.Results:
OK - The status indicates "FLOW" with the jumper wire in place. The ECM and the wiring are operating correctly. Proceed to Test Step 5.
Not OK - The status indicates "NO FLOW" with the jumper wire in place. There is a problem in the harness between the ECM and the connector for the coolant flow switch. There may be a problem with the ECM. Proceed to Test Step 6.Test Step 5. Check the Coolant Flow Switch
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.
Drain the engine coolant to a level that is below the coolant flow switch.
Remove the coolant flow switch from the engine.