Fan Resistor / High and Low Speed ​​Relay Failure (Cooling System)

• Most affected models: C3 (generations 1 and 2), Aircross, C3 Picasso and C4 Hatch/Pallas (1.4 8v, 1.5 8v and 1.6 16v naturally aspirated engines).
• What happens: The temperature gauge on the dashboard rises rapidly to the red zone (“STOP”) when the car encounters heavy traffic, but returns to normal as soon as the vehicle picks up speed on the highway. The air conditioning may also stop cooling intermittently.

What to check:

1. The first fan speed: Start the vehicle and turn the air conditioning to maximum. The radiator fan should immediately spin at a low, quiet speed. If it remains stationary and only starts much later, making a loud noise (second speed), the resistor is damaged.
2. The resistor connector: Located on the radiator’s plastic casing itself. Disconnect it (with the engine cold) and check for any melted or oxidized pins due to exposure to moisture from the front grille.
3. Control fuse in BSM: Generally associated with low-amperage circuits that send the electrical signal to the resistor.

Solution:

• Preventive: Preventive cleaning of the connector with contact cleaner during cooling system maintenance and ensuring that the front grille is not obstructed by leaves or dirt.
• Corrective: Replacing the part known as the “Fan Resistor” or “Electric Fan Resistor.” It is a low-cost and readily available part. When replacing it, it is recommended to also replace the wiring harness connector if it shows any signs of heat fatigue, preventing the problem from recurring in a few months.