U0174: Perte de communication avec le capteur E du système de retenue
Que faire
The airbag warning light is on and the car's crash sensing is not working properly. It drives normally; it should not be left.
A car with this many crash sensors usually has a system most owners have never heard of: pedestrian protection. A row of sensors across the front bumper works out whether the car has struck a person rather than an object, and if it decides it has, it lifts the back of the bonnet by several centimetres to put a crushable gap between the panel and the engine underneath — or on some cars fires an airbag across the bottom of the windscreen.
With this fault, that will not happen. It is protection for somebody outside your car rather than inside it, which is exactly why it gets put off and should not be.
Two things worth knowing. Those bonnet lifters fire at speeds low enough that the impact felt minor, and once fired they are single-use devices that must be replaced — the bonnet does not simply go back down. If anyone ever suggests pushing it back into place, do not let them: it leaves the bonnet insecure at speed.
For this fault, the thing to mention is the front bumper. These sensors live in it and bumpers get replaced for parking knocks all the time. A bumper refitted with the sensor wiring left unplugged, trapped or routed wrongly is the commonest cause — so any front-end work, however cosmetic, is worth telling the garage about.
Ce que signifie ce code
A restraints system sensor has stopped being heard from. See U0170 for the one-versus-several rule and U0475 for pedestrian protection, which is what a vehicle with this many sensors is likely to be doing.
The short version, because most owners have never heard of it: a row of sensors along the front bumper beam distinguishes a person from a bollard, and when it decides the object struck was a pedestrian, the vehicle fires actuators that lift the rear of the bonnet by several centimetres — putting a crushable gap between the panel and the hard engine components underneath — or deploys an airbag across the base of the windscreen.
A silent sensor in that row means the system cannot make that decision, so it will not fire. That is a protection for somebody outside the vehicle rather than inside it, which is precisely why it gets deferred and should not be.
Two facts follow that are worth knowing before any repair is discussed.
- The bonnet lifters are single-use pyrotechnic devices, exactly like an airbag. A vehicle whose lifters have fired is not repaired by pushing the bonnet back down — that is occasionally attempted and leaves the bonnet unlatched at speed.
- They fire at speeds low enough that the impact felt minor, so a vehicle bought second-hand may have had them fired and replaced, or fired and not.
And the practical cause is the bumper, which is the most frequently replaced panel on any vehicle. Bumper covers, beams and foam are changed for parking damage constantly, and the sensor tube or its loom must be transferred, refitted correctly and not pinched. A bumper fitted with the sensor wiring trapped, mis-routed or left unplugged is the commonest reason for this family of codes at the front of a vehicle — and unlike a mis-mounted sensor, an unplugged one produces exactly this: silence.
Causes probables
Commencez ici
Moins fréquent
- Faisceau de câblage endommagé · modérée
- Calculateur d'airbags défectueux · spécialisée
Symptômes
Composants concernés
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