What does P0480 cooling fan relay 1 control circuit mean?
Short answer: The engine computer found a problem in the circuit that controls cooling fan relay 1, such as an open, short or failed relay, which can lead to overheating or a fan that runs constantly.
Many engine computers control cooling fans through relays or a fan control module. P0480 points to the control side of relay 1, meaning the computer saw an open, short or unexpected voltage on the circuit it uses to switch the relay. Symptoms include a fan that never runs, causing overheating at idle and in traffic, or a fan that runs all the time.
Check the relay first by swapping it with an identical relay in the box or testing it on the bench. Then check the relay coil feed and the computer's command signal with a meter or scope while commanding the fan with a scan tool. Inspect the wiring and connector at the relay box and the computer for corrosion and heat damage. Some vehicles use a separate fan control module, so check service information for the circuit layout.
While the fan is inoperative, monitor coolant temperature closely. Keep hands clear of the fan, since it can start without warning even with the ignition off.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.