B009D: Right Side Restraints Sensor 4
What to do
Get this looked at promptly, and do not attempt it yourself. A restraint fault usually means the whole system has switched itself off, so the airbags and pretensioners may not fire in a crash — the car drives normally and is far less able to protect you. Never probe airbag wiring with a multimeter: the current an ordinary meter uses can set off the charge. Mention any door or sill damage, or a door that has been repaired or re-skinned — side sensors live inside the doors and pillars, and water reaching a sill connector is a common cause.
What this code means
The right side restraints crash sensor 4 circuit is faulty.
These are the crash sensors — the inputs that decide whether to deploy at all — and they are a different kind of component from everything else in this range.
Every other code in B00xx watches a device that fires. These watch the accelerometers that tell the module to fire it. A restraints module has its own sensor inside it, but a sensor in the middle of the car learns about an impact only once the structure has begun collapsing toward it. Remote sensors are mounted where the crash arrives first, so the decision can be made in the few milliseconds that exist.
That timing constraint is the whole design. A frontal airbag must be fully inflated about fifty milliseconds after impact; a side airbag has fifteen. A side impact leaves only the thickness of a door between the striking vehicle and the occupant, so its sensors sit in the doors, sills and pillars and must report almost instantly.
A fault here does not disable one device — it disables the decision. The module has lost part of the picture it uses to distinguish a severe crash from a pothole, so rather than risk deploying wrongly in either direction, it normally shuts the whole restraint system down.
And these sensors are the ones most often damaged by ordinary events. They live in the crumple zone and in the doors: a minor front-end knock, a door skin replaced, a kerbed sill, or water reaching a connector in a sill will all reach a crash sensor long before anything reaches an airbag.
Six side sensors per side means a long vehicle with three rows, each needing its own local detection — a strike at the third row must be sensed there, because a sensor at the B-pillar would learn about it far too late to protect anyone sitting over the rear axle.
Likely causes
Start here
- Corroded or loose connector · specialist
- Water ingress into connector · specialist
- Faulty restraints crash sensor · specialist
- Damaged wiring harness · specialist
Less common
- Faulty restraints control module · specialist
Symptoms
Components involved
Information, not instruction
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Community experience
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