OBD-II trouble code
B0090: Left Frontal Restraints Sensor (Subfault)
The airbag/SRS control module detected a fault in the left frontal restraints (impact) sensor circuit. Frontal airbag timing on that side may be affected, so this needs prompt professional attention.
Quick facts
- System
- Body
- Category
- Airbag / SRS Restraints
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $700
- DIY difficulty
- Shop recommended
What does B0090 mean?
B0090 is a body (B) code stored by the airbag control module. Its SAE-generic definition is 'Left Frontal Restraints Sensor,' referring to one of the forward-mounted impact (crash) sensors that tell the module a frontal collision is occurring on the left side of the vehicle. These sensors — often called front or forward crash sensors — are typically mounted low on the radiator support, front rails, or behind the front bumper, and their signal helps the module decide how and when to fire the frontal airbags and pretensioners.
The module sets B0090 when that sensor's circuit reads out of range — open, shorted, or with resistance outside the narrow band these safety circuits demand — or when the sensor stops reporting valid data. Because a frontal impact sensor lives at the very front of the car, its wiring and connector are exposed to moisture, road spray, salt, and minor front-end impacts, which is why connector corrosion and harness damage are among the most common causes. As with all B-codes, confirm the exact definition and sensor location against your make's service data.
This is a supplemental restraint fault, not a driveability fault: the vehicle drives normally, but frontal airbag deployment timing on the affected side may be compromised in a crash, and airbag circuits carry a small risk of unintended deployment when mishandled. SRS diagnosis and repair should be performed by a qualified technician who can safely disable the system, and the fault should not be left unrepaired.
Common causes
- Corroded, wet, or loose connector at the front impact sensor
- Damaged wiring in the front harness (road debris, salt, or minor front-end impact)
- Failed left frontal impact/crash sensor
- Prior front-end collision or bumper/radiator-support repair that disturbed the sensor
- Sensor replaced but not the correct part, or not properly mounted
- Faulty airbag/SRS control module
Symptoms
- Airbag / SRS warning light on
- Stored B0090 fault in the restraints module
- No effect on engine or driving performance
- Possible additional side or frontal restraint-sensor codes stored alongside it
Diagnostic steps
- 1.Use a scan tool that can access the airbag/SRS module and record B0090 and any companion restraint-sensor codes.
- 2.Confirm the exact sensor location for the specific make and model, since front impact sensors are mounted differently across manufacturers.
- 3.With the system safely disabled per service procedure, inspect the front impact-sensor connector and harness for corrosion, moisture, or impact damage.
- 4.Pay attention to the area behind the bumper and on the radiator support/front rails, where these sensors and their connectors are exposed to the elements.
- 5.Measure the sensor circuit's resistance against specification to separate a wiring fault from a failed sensor.
- 6.If the sensor was recently replaced, verify it is the correct part, correctly torqued, and fully seated (mounting affects the signal).
- 7.Repair wiring/connector faults or replace the indicated sensor, then clear codes and confirm the SRS light stays off.
Repair cost
$100 – $700
A connector or wiring repair can be modest, while replacing a front impact sensor commonly runs $150-$500 including diagnosis. Costs rise if the front bumper or structure must come apart to reach the sensor, or if the airbag/SRS control module itself is at fault. SRS work should be done by a qualified technician, so plan for professional diagnostic time.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with airbag / srs crash sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.