Cooling Fan Always On (LDK, LHU, LBW, or LAU)
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Cooling Fan Always On (LDK, LHU, LBW, or LAU)
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Circuit/System Description
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The engine cooling fan system is composed of two fans, 7 relays, the engine control module (ECM), and the associated wiring. Each fan assembly includes one resistor, which enables the ECM to operate the engine cooling fans at 3 speeds using two control circuits. The ECM activates the applicable relay by grounding the control circuit with a solid state device called a driver. Each driver is equipped with a feedback circuit that is pulled-up to a voltage. The ECM can determine if the control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage. The cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G106.
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The scan tool cooling fan output control operates as follows:
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Cooling Fan Relay 1 operates both fans at a medium speed
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Cooling Fan Relay 2 and 3 operates both fans at a low speed
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Cooling Fan Relay 1, 2 and 3 operates both fans at a high speed
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When disconnecting or removing fuses and relays from a fuse block, always inspect the component electrical terminals for corrosion and the correct orientation in the fuse block. Test the mating electrical terminals for tightness.
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Schematic Reference
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation (LHU/A20NFT, LAU/A28NER)
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
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Circuit/System Verification
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1.
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Ignition ON, observe the DTC information with a scan tool. Verify that DTCs P0480, P0481, P0691, P0692, P0693 or P0694 are not set.
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3.
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Ignition ON, observe the scan tool Cooling Fan Relay 1 and Cooling Fan Relays 2 and 3 Command parameters. The parameters should display OFF.
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4.
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Ignition ON, observe that the fans are not ON.
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Both Fans ON
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1.
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Ignition OFF, disconnect the KR20F cooling fan relay.
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2.
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Ignition ON, verify that the cooling fans are not ON.
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3.
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If the fans are OFF, test or replace KR20F relay.
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4.
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Ignition OFF, disconnect the KR20C cooling fan low speed relay.
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5.
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Ignition ON, verify that the cooling fans are not ON.
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6.
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If the fans are OFF, test or replace KR20C relay.
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7.
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Ignition OFF, disconnect the KR20M cooling fan left medium speed relay.
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8.
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If the fans continue to operate, test the circuits listed below for:
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A short to ground in the KR20F relay switched control circuit for the X70 under hood relay block.
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A short to voltage in KR20C relay switched output circuit.
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A short to voltage in KR20M relay switched output circuit.
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9.
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If all circuits test normal, test or replace the KR20M relay.
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One Fan ON
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1.
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Ignition OFF, disconnect the KR20D cooling fan high speed relay.
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2.
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Ignition ON, verify that the cooling fan is not ON.
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3.
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If the fan is OFF, test or replace KR20D relay.
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4.
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Ignition OFF, disconnect the KR20N cooling fan right medium speed relay.
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5.
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Ignition ON, verify that the cooling fan is not ON.
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6.
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If the fan continues to operate, test the circuits listed below for:
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A short to voltage in KR20D relay switched output circuit.
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A short to voltage in KR20N relay switched output circuit.
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7.
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If all circuits test normal, test or replace the KR20N relay.
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Relay Replacement (Attached to Wire Harness)
