Technical Description of OBD-II Trouble Code
Control Circuit for Cooling Fan Relay 2
What does that signify?
This is a generic diagnostic trouble code (DTC) for powertrain issues, which applies to all makes and models manufactured from 1996 onwards. However, the specific troubleshooting steps may vary depending on the vehicle.
If the check engine light in your vehicle illuminates and you retrieve the code P0481, it indicates a problem with the engine cooling fan circuit. This code is applicable to all OBD II vehicles (on board diagnostics).
While driving, the engine is effectively cooled by a sufficient amount of air passing through the radiator. However, when the car comes to a stop, no air flows through the radiator, causing the engine temperature to rise.
The powertrain control module (PCM) detects the increase in engine temperature through the coolant temperature sensor (CTS) located near the thermostat. When the temperature reaches approximately 223 degrees F (specific value depends on the make, model, and engine), the PCM commands the cooling fan relay to activate the fan by providing a ground connection to the relay.
A problem within this circuit prevents the fan from operating, leading to engine overheating while the vehicle is stationary or moving at a slow speed. When the PCM attempts to activate the fan and detects a mismatch between the command and the result, it sets the P0481 code.
NOTE: Although P0481 refers to the basic circuit, codes P0480 and P0482 indicate the same problem but with different fan speed relays.
Symptoms
The symptoms may include:
Potential Causes
The potential causes for this DTC may include:
Diagnostic and Repair Procedures
It is always advisable to check the technical service bulletins (TSB) related to this code for your specific vehicle. These bulletins provide information on common complaints received by the dealer service department and the manufacturer’s recommended repairs. You can search for TSBs using your preferred search engine by entering “technical service bulletins for [your vehicle model].” This is also a good practice before purchasing a vehicle.
Many vehicles have two engine fans – one for engine cooling and the other for cooling the air conditioning condenser and providing additional cooling for the engine.
The main cooling fan, which is not located in front of the air conditioning condenser, should be the primary focus for inspection. Additionally, some vehicles have multi-speed fans that require up to three fan speed relays for low, medium, and high speeds.
Perform a visual inspection by opening the hood. Check for any obstructions in front of the radiator that may block airflow. Spin the fan with your finger (ensure that the vehicle and key are turned off). If the fan does not spin, it indicates that the fan bearings are worn out and the fan needs to be replaced.
Inspect the electrical connection at the fan. Disconnect the connector and look for any corrosion or bent pins. Repair if necessary and apply dielectric grease to the terminals.
Open the fuse block and examine the cooling fan relay fuses. If they are in good condition, remove the cooling fan relays. The bottom of the fuse block lid usually indicates their placement, but if not, refer to the owner’s manual.
It is important to note that the vehicle’s PCM functions as a ground to operate components, rather than supplying power. The fan relays act as remote light switches. Since the fan and other components draw too much amperage to be safe in the cockpit, they are located under the hood.
Each relay in the fuse block has a constant power supply from the battery on one terminal. This terminal activates the fan when the circuit is closed. Another terminal receives power only when the key is turned on. The negative terminal in this circuit is used by the PCM to activate the relay by grounding it.
Refer to the circuit diagram displayed on the side of the relay. Look for a simple open and shut circuit. Verify the constant power supply from the battery positive terminal in the relay block. The opposite side of the circuit connects to the fan. Use a test light to identify the hot terminal.
Jump the battery terminal to the fan harness terminal, and the fan should start operating. If it does not, disconnect the fan connection at the fan and use an ohmmeter to check the continuity between the fan side of the relay terminal and the connector at the fan. If there is continuity, it indicates a faulty fan. If there is no continuity, it suggests a faulty harness between the fuse block and the fan.
If the fan operates, check the relays. Look for the switched power terminal on the side of the relay or simply turn the key on. Check the terminals for an additional power terminal and determine its location on the relay.
Jump the battery plus terminal from the first test with this switched terminal, and connect an additional jumper from the negative terminal on the relay to ground. The switch should click on. Use an ohmmeter to test the continuity between the constant battery terminal and the fan harness terminal, indicating that the circuit has closed.
If the circuit does not close or the relay does not click, it indicates a faulty relay. Repeat the same testing procedure for all the relays to ensure they are all functioning properly.
If there is no switched power at the relay, suspect a problem with the ignition switch.
If all the relays prove to be good, check the coolant temperature sensor (CTS) using an ohmmeter. Disconnect the connector and allow the engine to cool down. Set the ohmmeter to the 200,000 scale and probe the sensor terminals.
The reading should be approximately 2.5. For precise readings, consult a service manual. Accuracy is not crucial as different sensors may have varying readings. The goal is to determine if the sensor is functioning. Reconnect the sensor and warm up the engine.
Turn off the engine and disconnect the CTS plug again. Check it with the ohmmeter, and there should be a significant change in resistance. If there is no change, it indicates a faulty sensor.
If the above procedures do not identify any failures, there is a possibility of a poor connection to the PCM or a faulty PCM itself. Do not proceed further without consulting the service manual. Disconnecting the PCM could result in loss of programming, and the vehicle may not start unless it is towed to the dealer for reprogramming.
