What does it mean?
This is a generic powertrain diagnostic trouble code (DTC), meaning it covers all makes/models from 1996 onward. However, specific troubleshooting steps vary by vehicle.
If your vehicle’s check engine light comes on and after retrieving the code you find P0481 displayed, it refers to the engine cooling fan circuit. This is a generic code applying to all OBD-II vehicles.
While driving, sufficient air passes through the radiator to effectively cool the engine. When you stop the car, no air flows through the radiator and the engine temperature begins to rise.
The PCM detects the engine temperature increase via the Coolant Temperature Sensor located near the thermostat. When the temperature reaches approximately 223°F (the exact value depends on make/model/engine), the PCM commands the cooling fan relay to activate the fan by providing ground to the relay.
There’s a problem in this circuit causing the fan not to operate, allowing the engine to overheat when stationary or at low speeds. When the PCM attempts to activate the fan and detects that the command and result don’t match, the code is set.
NOTE: P0481 refers to the primary circuit, while P0480 and P0482 relate to the same issue but concern different fan speed relays.
Symptoms
Symptoms may include:
Check engine light illumination with P0481 code stored
Engine temperature rising when vehicle is stopped and idlingPotential Causes
Causes of this DTC may include:
Faulty cooling fan control relay 2
Open or shorted cooling fan control relay harness
Poor electrical connections in the circuit
Faulty cooling fan 2
Defective coolant temperature sensor
Open or shorted cooling fan harness
Poor electrical connection in cooling fan circuit
Intake Air Temperature (IAT) sensor failure
Air conditioning selector
A/C refrigerant pressure sensor
Vehicle Speed Sensor (VSS)Diagnostic and Repair Procedures
It’s always wise to consult Technical Service Bulletins for your specific vehicle to see what types of complaints have been submitted regarding this code. Search using your preferred search engine for “technical service bulletins for…” Look for the code and manufacturer-recommended repair type. This is also good practice before purchasing a vehicle.
Many vehicles have two engine fans – one for engine cooling and a second for A/C condenser cooling and additional engine cooling.
The fan not in front of the A/C condenser is the primary cooling fan and should be the initial focus. Additionally, many vehicles have multi-speed fans requiring up to three fan speed relays for low, medium, and high speeds.
Open the hood and perform a visual inspection. Check the fan and ensure there are no obstructions in front of the radiator blocking airflow. Spin the fan with your finger (ensure vehicle and ignition are off). If it doesn’t spin, the fan bearings are seized and the fan is bad.
Check the electrical connection to the fan. Separate the connector and look for corrosion or bent pins. Repair if necessary and use dielectric grease on the terminals.
Open the fuse box and inspect the cooling fan relay fuses. If they’re good, remove the cooling fan relays. The underside of the fuse box cover usually indicates locations, otherwise check the owner’s manual.
The vehicle PCM’s function is to act as ground for operating components, not to provide power. Fan relays are essentially remote light switches. The fan and other devices draw too much amperage to be safely located in the cockpit, so they’re kept under the hood.
A constant battery power supply is present on one terminal of each relay. This powers the fan when the circuit is closed. A switched terminal will only be hot when the key is activated. The ground terminal of this circuit is used when the PCM wants to activate the relay by grounding it.
Look at the circuit diagram on the side of the relay. Identify the simple open and closed circuit. Check for constant battery power at the positive terminal in the relay block. The opposite side goes to the fan. Use a test light to locate the hot terminal.
Jump the battery terminal to the fan harness terminal and the fan should operate. If not, disconnect the fan connection at the fan and using an ohmmeter, check continuity between the fan side of the relay terminal and the fan connector. If there’s continuity, the fan is bad. Otherwise, the harness between the fuse block and fan is faulty.
If the fan operated, check the relays. Look at the side of the relay for the switched power terminal or simply turn the key. Check terminals for additional power supply and identify their locations on the relay.
Jump the battery positive terminal from the first test with this switched terminal and place an additional jumper from the relay ground terminal to ground. The switch should click on. Use an ohmmeter to verify that the constant battery terminal and fan harness terminal have continuity, meaning the circuit is closed.
If the circuit didn’t close or the relay didn’t click, the relay is bad. Check all relays similarly to ensure they all function.
If there was no switched power to the relay, the ignition switch is suspect.
If these prove good, check the CTS with an ohmmeter. Remove the connector. Let the engine cool and set the ohmmeter to the 200,000 ohm scale. Probe the sensor terminals.
The reading will be approximately 2.5. For accurate readings, consult a service manual. Precision isn’t necessary as all sensors may differ – you just want to know if it’s working. Reconnect it and warm up the engine.
Stop the engine and pull the CTS plug again. Check it with the ohmmeter – there should be a significant resistance change, otherwise the sensor is bad.
If the above procedure didn’t find a failure, the likely cause is either a poor connection to the PCM or the PCM itself. Don’t proceed further without consulting your service manual. Disconnecting the PCM can cause programming loss and the vehicle may not start unless towed to the dealer for reprogramming.
P0481 Cooling Fan Relay 2 Control Circuit
Posted by