P0485 Code: Cooling Fan Power/Ground Circuit

What the P0485 code means

The electric fan pulls air through the radiator when the vehicle is moving slowly or stopped, and when the air conditioning is on. The computer turns it on with relays or with a speed control module.

The computer monitors the control circuit from its own driver transistor. The P0485 code indicates a fault in the power supply or the ground of the component. Before replacing the component, check the fuse, relay, connector and wiring, since they are the most common cause.

If the fan does not run, the engine overheats in slow traffic and the A/C cools poorly. If it runs all the time, it drains the battery. Keep an eye on the temperature gauge until it is repaired.

Check the voltage at the connector with the component running. A big drop compared with the battery means a power supply or a ground with resistance in it. Measure the voltage drop across the ground wire, which should be less than 0.2 V under load.

P0485 code symptoms

• Check engine light on.
• Overheating in traffic or when stopped.
• A/C that cools poorly when stopped.
• Fan that never shuts off.

Likely causes of the P0485 code

1. Fuse or relay blown or with worn contacts.
2. Loose or corroded ground. It adds resistance to the circuit.
3. Power wire damaged by heat or rubbing.

How to diagnose the P0485 code step by step

1. Command the component with the scan tool and check whether it responds.
2. Check the fuse and relay.
3. Measure the supply at the connector: battery voltage with the key on or when it is commanded.
4. Measure the component resistance and compare it with the manual. Also check the insulation to ground.
5. Check the control wire for continuity and for shorts.
6. Command the fan with the scan tool or by turning on the air conditioning.
7. Measure the fan current. A worn motor draws too much.
8. Check the high-current fuses.

How to fix the P0485 code

• Repair the connector, the wiring or the power supply.
• Replace the cooling fan if it does not respond with correct power and control.
• Clear the codes and verify that the monitor completes.

Technical reference data

• Typical draw: 10 to 30 A per fan.
• Maximum voltage drop on the ground wire under load: 0.2 V.
• Approximate values only: check the manufacturer data for your engine.

Brand-specific notes

On many vehicles the two-speed fan uses resistors or a PWM module that burns out when the motor wears down.

Clean the ground connection down to bare metal before you condemn the fan, since a poor ground mimics a bad motor.

Frequently asked questions about P0485