Cooling Fan Inoperative (LF1)
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Cooling Fan Inoperative (LF1)
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Circuit/System Description
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The engine cooling fan system is composed of one cooling fan, a series of 5 relays, the engine control module (ECM), and the associated wiring. The cooling fan assembly includes two individual resistors mounted to each side of the cooling fan shroud. This combination of components enables the ECM to operate the cooling fan at 3 speeds using two fan control circuits.
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The scan tool cooling fan output control operates as follows:
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Cooling Fan Relay 1 operates the fan at a low speed
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Cooling Fan Relay 2 and 3 operates the fan at a medium speed
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Cooling Fan Relay 1, 2 and 3 operates the fan 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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If the cooling fan operates at high speed when the ECM is requesting medium speed operation, test or replace the KR20E cooling fan speed control relay and X50A UBEC.
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Schematic Reference
Engine Cooling Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Cooling Fan Description and Operation (LF1)
Cooling Fan Description and Operation (LAU)
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 DTC P0480 or P0481 is not set.
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3.
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Command the cooling fan ON and OFF at low, medium, and high speed with a scan tool. The cooling fan should turn ON and OFF in each of the commanded states.
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1.
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Ignition OFF, disconnect the following relays:
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2.
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Ignition ON, verify a test lamp illuminates between the KR20C relay coil ignition voltage circuit terminal 86 and ground.
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3.
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If the test lamp does not illuminate, test the relay voltage supply circuit for an open/high resistance.
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4.
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Ignition ON, command the cooling fan ON at low speed.
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5.
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Connect a test lamp between B+ and the KR20C relay control circuit terminal 85. The test lamp should illuminate.
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6.
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Note
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The KR20C relay is controlled through the switch side of the KR20F COOL FAN 4 relay.
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If the test lamp does not illuminate, test the relay control circuit for an open/high resistance. If the circuit tests normal, test or replace the X50A underhood fuse block (UBEC).
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7.
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Ignition ON, command the cooling fan ON at high speed.
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8.
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Connect a test lamp between ground and the KR20D relay coil ignition voltage terminal 85. The test lamp should illuminate.
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9.
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Note
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The ignition voltage for the KR20D relay coil is supplied through the switch side of the KR20E COOL FAN 5 relay.
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If the test lamp does not illuminate, test or replace the X50A underhood fuse block (UBEC).
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10.
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Ignition OFF, install the previously removed KR20 cooling fan relays.
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11.
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Disconnect the harness connectors at the G10 cooling fan and both R10 cooling fan resistors.
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12.
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Test for less than 1.0Ω between the G10 engine cooling fan ground circuit terminal 1 and ground.
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13.
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If greater than the specified range, test the ground circuit for an open/high resistance.
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14.
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Ignition ON, connect a test lamp between ground and the cooling fan circuit terminals listed below. Command the cooling fan ON at High speed. The test lamp should illuminate at each terminal.
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R10R low speed cooling fan resistor terminal 1
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R10L medium speed cooling fan resistor terminal 1
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G10 cooling fan B+ supply circuit terminal 2
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15.
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If the test lamp does not illuminate, test the appropriate KR20 relay controlled output and B+ supply circuits for a short to ground or for an open/high resistance. If the circuits test normal, test or replace the appropriate KR20P, KR20C, or KR20D cooling fan relay.
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16.
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Ignition OFF, connect the harness connectors to the R10 cooling fan resistors.
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17.
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Ignition ON, connect a test lamp between ground and the G10 cooling fan B+ supply circuit terminal 2. Command the cooling fan ON at Low and Medium speed. The test lamp should illuminate as commanded in each speed.
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18.
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If the test lamp does not illuminate, test or replace the appropriate R10 cooling fan resistor.
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19.
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If all of the circuits and components test normal, test or replace the G10 cooling fan.
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1.
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Ignition OFF, disconnect the cooling fan relay.
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2.
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Test for 60-100 Ω between terminals 85 and 86.
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3.
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If not within the specified range, replace the KR20 cooling fan relay.
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4.
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Measure the resistance between the terminals listed below. The DMM should display OL.
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If not the specified range, replace the relay.
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5.
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Install a 20 A fused jumper wire between relay terminal 86 and B+. Install a jumper wire between relay terminal 85 and ground. Test for less than 2Ω between terminals 30 and 87.
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6.
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If greater than the specified range, replace the relay.
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Cool Fan 5 Printed Circuit Board Relay
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1.
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Ignition OFF, disconnect the following cooling fan relays:
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2.
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Test for 190-230 Ω between Cool Fan 3 relay terminals 85 and 86 in the UBEC.
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3.
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If not within the specified range, replace the X50A UBEC.
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4.
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Measure the resistance between the Cool Fan 3 relay terminal 86 and Cool Fan 1 relay terminal 85 at the UBEC. The DMM should display OL.
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5.
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If less than the specified range, replace the X50A UBEC.
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6.
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Connect a 3 A fused jumper wire between ground and Cool Fan 3 relay terminal 85, at the UBEC.
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7.
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Ignition ON, verify a test lamp illuminates between ground and Cool Fan 1 relay terminal 85, at the UBEC.
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8.
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If the test lamp does not illuminate, replace the X50A UBEC.
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
