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P0480 Diagnostic and Fix for 2003 Monte Carlo: Fan Relay, Sensor, and Wiring Issues

Model: 2003 Monte Carlo Fault Code: P0480 Posted: 2017-05-18 13:31

I own a 2003 Monte Carlo with the check engine light on. I recently received a P0480 diagnostic code indicating an issue with the fan control circuit. I replaced the thermostat sensor, which temporarily cleared the code, but it returned shortly after. The cooling fans activate only at idle and when engine temperature reaches approximately 185–190°F. The vehicle does not overheat, and the system appears to be functioning normally. However, when I took it back to AutoZone, they confirmed the same P0480 code. I suspect a relay or wiring issue in the underhood fan control circuit.

Related fault codes

P0480

Comments (7)

Anonymous 2017-05-18 14:04

The P0480 code is related to Fan Relay Circuit #1, not the temperature sensor. Check the underhood fuse box — specifically, the 25-amp fan control #1 fuse and the corresponding relay. There are two fuse boxes: one on top and one at the bottom of the engine bay. Your owner's manual will provide detailed diagrams if you're having trouble locating these components. AutoZone sells replacement parts for this issue.

Anonymous 2017-05-19 10:43

I replaced the fan relay, but the P0480 code persists.

Anonymous 2017-05-21 08:58

Have you checked the fuses? A digital multimeter (DVOM) and wiring diagram are essential tools to verify voltage and circuit continuity. Use them to test the green wire for proper signal from the Powertrain Control Module (PCM).

Anonymous 2017-05-21 12:04

Yes, I've checked all fuses — they are in good condition. What is a DVOM and how do I use a wiring diagram?

Anonymous 2017-05-21 15:02

The P0480 code suggests the PCM isn't detecting correct voltage on the green wire. Confirm that the two wires you identified have proper 12V supply (with no open circuits). Try swapping Relay #1 with Relay #2 — if the code clears, it confirms a faulty relay. Also, ensure there are no aftermarket systems like remote starters or alarms interfering with the fan control circuit.

Anonymous 2019-07-13 08:09

Are both cooling fans supposed to activate simultaneously? I've checked fuses and relays and replaced the fan assembly — only the driver's side fan operates. The passenger-side fan does not turn on at all.

Anonymous 2019-07-13 09:56

Initially, both fans operate slowly; as engine temperature rises, they switch to high speed. However, only one fan (driver’s side) activates fully. Check the circuit for Fan Control #2 and #3 — verify fuses and relays in that path. A faulty connection here could cause partial operation or code persistence.