Vanne de dérivation du circuit de refroidissement défectueuse

The valve that routes coolant around the radiator during warm-up has failed or stuck.

It exists because a cold engine is an inefficient and dirty one. Oil is thick, clearances are wrong, and the catalyst is not lit — so the fastest possible warm-up is worth real fuel and real emissions. The bypass valve achieves it by keeping coolant away from the radiator entirely until the engine is up to temperature, so the small volume in the block heats quickly rather than the whole system heating slowly.

Which direction it sticks decides the symptom, and one of them is effectively invisible. Stuck in bypass, the engine warms fast and then keeps warming — the temperature gauge climbs, and the driver notices. Stuck open to the radiator, the engine simply never warms properly: slower warm-up, worse economy, a heater that takes forever to produce heat, and no warning for weeks. That second one is the common failure and the one nobody reports, because a car that is merely slow to warm up does not feel broken.

A valve fails by sticking, so the position feedback is what finds it. A control circuit that tests good proves the command was sent, not that anything moved — which is why these valves carry a position sensor and why a performance code matters more here than a circuit code.

Ask which way the symptoms point — slow to warm, or running hot — because they indicate opposite stuck positions and different repairs.