P0481
DTC P0480 or P0481
Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Diagnostic System Check - Vehicle
• Review Strategy Based Diagnosis for an overview of the diagnostic approach. Strategy Based Diagnosis
• Diagnostic Procedure Instructions provides an overview of each diagnostic category. Diagnostic Procedure Instructions
DTC Descriptors
DTC P0480: Cooling Fan Relay 1 Control Circuit
DTC P0481: Cooling Fan Relay 2 and 3 Control Circuit
Diagnostic Fault Information
Typical Scan Tool Data
FC Relay 1, and FC Relays 2 and 3 Ckt Open, Short Gnd, and Short Volts Test Status with component OFF
FC Relay 1, and FC Relays 2 and 3 Ckt Open, Short Gnd, and Short Volts Test Status with component ON
Circuit/System Description
The engine cooling fan system consists of a cooling fan assembly containing two electric cooling fans. The engine control module (ECM) uses two fan control circuits and a series of three relays to command the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.
Conditions for Running the DTC
• The engine speed is greater than 400 RPM.
• The ignition voltage is between 11�18 volts.
• The relay control circuit is commanded from OFF to ON, or ON to OFF.
• DTC P0480 and P0481 run continuously when the conditions above are met.
Conditions for Setting the DTC
P0480
The commanded state of the ECM driver and the actual state of the control circuit do not match for greater than 5 seconds.
P0481
The commanded state of the ECM driver and the actual state of the control circuit do not match for greater than 5 seconds.
Action Taken When the DTC Sets
DTCs P0480 and P0481 are Type B DTCs.
Conditions for Clearing the DTC
DTCs P0480 and P0481 are Type B DTCs.
Diagnostic Aids
• The ECM has the capability of providing command to the fan relays even when a scan tool output control is being used. Always refer to the fan control command parameters on the scan tool to know which fans are being commanded ON by the ECM.
• The scan tool cooling fan control function operates as follows:
- Fan Relay 1 operates both fans at a low speed
- Fan Relay 2 and 3 operates the right fan at a high speed
- Fan Relay 1, 2 and 3 operates both fans at a high speed
• 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.
Reference Information
Schematic Reference
Engine Cooling Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Connector Views
Description and Operation
Cooling Fan Description and Operation Cooling Fan Description and Operation
Electrical Information Reference
• Circuit Testing Circuit Testing
• Connector Repairs Connector Repairs
• Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Scan tool information Scan Tool Testing and Procedures
Circuit/System Verification
1. Engine operating, observe the DTC information with a scan tool. DTC P0480 or P0481 should not set.
2. Command the cooling fans ON and OFF at high speed while observing the scan tool circuit test status parameters listed below:
• FC Relay 1 Ckt Open, Short Gnd, and Short Volts Test Status
• FC Relay 2 and 3 Ckt Open, Short Gnd, and Short Volts Test Status
• The parameters should display OK or Not Run in each of the commanded states.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
1. Ignition OFF, disconnect all of the KR20 cooling fan relays.
2. Ignition ON, verify that a test lamp illuminates between ground and the relay coil ignition circuit terminal listed below:
• Fan 1 relay, terminal 86
• Fan 2 relay, terminal 86
• Fan 3 relay, terminal 85
--> If the test lamp does not illuminate, test the relay coil ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.
Note: The following tests must be performed on all three fan relay control circuits.
3. Connect the red lead of the DMM to a control circuit terminal listed below. Connect the black lead to ground. Set the DMM on the diode setting. The DMM should display OL.
• Fan 1 relay, terminal 85
• Fan 2 relay, terminal 85
• Fan 3 relay, terminal 86
--> If less than the specified range, test the appropriate relay coil control circuit for a short to ground. If the circuit tests normal, replace the K20 ECM.
Note: The following test must be performed on all three fan relay circuits.
4. Command the cooling fan relay ON and OFF with a scan tool. The DMM should transition from OL when commanded OFF to less than 1 Volts when commanded ON.
--> If the circuit voltage does not correspond to the specified values, test the control circuit for an open/high resistance or a short to voltage. If the circuit tests normal, replace the K20 ECM.
5. If all circuits test normal, test or replace the appropriate KR20 relay.
Component Testing
1. Ignition OFF, disconnect the KR20 cooling fan relay.
2. Test for 70-110 Ohms between terminals 85 and 86.
--> If not within the specified range, replace the KR20 cooling fan relay.
3. Measure the resistance between the terminals listed below. The DMM should display OL.
• 30 and 86
• 30 and 87
• 30 and 85
• 85 and 87
--> If less than the specified range, replace the KR20 cooling fan relay.
--> If less than the specified range, replace the KR20 cooling fan relay.
--> If less than the specified range, replace the KR20 cooling fan relay.
4. Test the Fan 2 relay for less than 2 Ohms between terminals 30 and 87A.
--> If greater than the specified range, replace the Fan 2 relay.
5. Connect a 20 A fused jumper wire between relay terminal 85 and B+. Connect a jumper wire between relay terminal 86 and ground. Test for less than 2 Ohms between terminals 30 and 87.
--> If greater than the specified range, replace the KR20 cooling fan relay.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
• Accessory Wiring Junction Block Replacement Accessory Wiring Junction Block Replacement
• Relay Replacement Service and Repair
• Engine Coolant Fan Motor Replacement Service and Repair
• ECM replacement Service and Repair
• ECM setup, and programming Testing and Inspection