B0099 – Rollover Sensor (OBD2)
B0099 means "Rollover Sensor". Crash sensors in the front and sides of the car detect an impact and tell the airbag module to deploy; these codes mean a frontal, side or rollover sensor is faulty, not communicating or implausible.
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B0099 quick summary
| Fault code | B0099 |
|---|---|
| Meaning | Rollover Sensor |
| System | Body |
| Vehicles | Generic OBD2 |
| Severity | High |
| Can I drive? | The car drives normally, but some airbags may not deploy in a crash. Have it repaired as soon as possible. |
| Repair cost | €40 – €500 |
How airbag crash sensors work
Besides the acceleration sensor inside the airbag module, most cars have external crash sensors: frontal sensors near the radiator support, side sensors in the B-pillars or doors (acceleration or pressure sensors) and sometimes a rollover sensor. They allow the airbag module to detect an impact early and decide which airbags to deploy.
The airbag module checks every sensor at start-up and continuously while driving. Codes report a sensor that does not respond, a wrong signal, an internal fault or a wrong sensor fitted.
Front sensors are exposed to water and minor collisions; door sensors suffer from water in the door and damaged wiring in the door hinge. After a crash, sensors often have to be replaced even if the airbags did not deploy.
B0099 is a body code from the standard (SAE) restraint system range. Some manufacturers use their own numbering for airbag codes, so always check the text your scan tool shows for your vehicle.
Symptoms of B0099
- Airbag warning light on
- Code after a minor collision or front-end repair
- Code after door or interior work
- Water in the door or footwell
- No other symptoms
Most common causes of B0099 (most likely first)
Mechanic's Pro Tip
Crash sensors must be bolted on with the correct torque and orientation – a loose sensor or one from another model can read wrongly and set a code even though it works.
1.Damaged sensor after a minor collision
Most likely2.Water in a door or on the sensor connector
3.Broken wire in the door hinge area
4.Wrong sensor fitted or sensor not mounted tightly
5.Airbag module fault
Step-by-step diagnostic guide
- 1
Read airbag codes
Read the airbag module and identify which sensor is affected.
- 2
Disconnect safely
Disconnect the battery and wait the time specified by the manufacturer before working on airbag components.
- 3
Inspect sensor and mounting
Check the sensor for damage, correct part number and a firm mounting, and the connector for water and corrosion.
- 4
Check wiring
Check the wiring, especially in the door hinge area, for breaks.
- 5
Replace and clear
Replace the sensor with the correct part, reconnect, clear codes and confirm the warning light goes out.
Frequently asked questions
Can I keep driving with B0099?
The car drives normally, but some airbags may not deploy in a crash. Have it repaired as soon as possible.
How much does it cost to fix B0099?
Typical repair costs are 40 € – 500 €, depending on the cause and the vehicle. The most common fixes are: damaged sensor after a minor collision; water in a door or on the sensor connector; broken wire in the door hinge area. Always confirm the cause with the tests above before buying parts.
Do crash sensors need replacing after an accident?
Often yes, depending on the manufacturer's instructions, even if the airbags did not deploy.
Will the car pass inspection with this fault?
In most countries an active airbag warning light is a reason to fail the inspection.
What is the difference between B0099 and similar codes?
B0099 belongs to a group of codes for the same component that differ in the type or location of the fault: B0096 – Right Side Restraint Sensor 1; B0097 – Right Side Restraint Sensor 2; B0098 – Right Side Restraint Sensor 3; B009A – Left Side Restraint Sensor 4; B009B – Left Side Restraint Sensor 5; B009C – Left Side Restraint Sensor 6. The tests on this page apply to the whole group; the type of fault tells you where to start.
Related fault codes
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.