1998 Audi A4 Air Bag Crash Sensor Replacement Cost

The crash sensor is the first line of detection in the event of a collision. It alerts the supplemental restraint system (SRS) of the impact, and the SRS control module will then decide which airbags should be deployed, if any. This is a small electronic switch, and there will be several placed in strategic locations around the vehicle. This ensures that the vehicle will recognize a collision from any direction.

In the event of a collision and if that collision is severe enough, the crash sensor, a.k.a. airbag sensor, will sense the sudden deceleration of the vehicle by forcing a connection inside the sensor. When this connection inside the sensor is forced, either by a cam or a metallic ball, the crash sensor will send a signal to the SRS computer, which, as mentioned, will detect passenger seating positions, where airbags are needed, lock the seat belts, shut off the engine, and deploy the airbags as needed.

When an airbag sensor or crash sensor has failed, the airbag warning light, which differs by vehicle year, make and model, will illuminate, alerting the driver that there is an issue detected in the SRS system. In some instances, the check engine light may illuminate in conjunction with the airbag light. In this case, the vehicle would likely not crank or start until the trouble code is cleared, again, depending on year, make, and model. Lastly, airbag deployment is a major symptom of crash sensor function, but typically failure will not cause the airbags to be incapable of deployment.

Driving a vehicle with a faulty airbag sensor means that the airbags will not function in the event of an accident. Not only is this extremely risky, but if the airbags are not operational the vehicle will not pass any state or federal inspections. Any time the airbag warning light is displayed, immediate action should be taken to correct the fault, but the vehicle will be able to drive until that issue is repaired.

Airbags tend to fail for two reasons, and neither are predictable. Collisions with any object with enough mass to trip the airbag deployment sensor will likely necessitate replacement due to physical damage to the sensor. This can happen within one mile of ownership, or never at all. Secondly, and typically for older cars, vehicles in humid climates, or vehicles which are subject to road sale and corrosion, the crash sensors can become rusted. In the event the sensor becomes rusted, this rust and corrosion can cause a short or open circuit situation, causing the sensor to illuminate the airbag warning light. Again, this depends on age and operating environment.

When diagnosing an airbag system, a physical inspection of the vehicle may be conducted first, if there is obvious damage or cause for concern. Generally speaking, the servicing technician will use a professional grade computerized scan tool with the ability to read and verify diagnostic codes and enhanced diagnostic trouble codes. This will generally direct the technician to the exact fault when working with the SRS system, however, further diagnostics may be required. For instance, if the vehicle has an issue with a crash sensor circuit, the technician will need to test the circuit, not just the crash sensor.

Once a crash sensor has been identified and proven faulty, the battery will be disconnected, and obstructions like body panels, headlights, bumper covers, or interior trim will be removed, if not already, to access the failed crash sensor. The crash sensor will need to be dismounted and disconnected electrically, and the new crash sensor will be installed. Prior to reassembling any obstructing components, the system will be tested once again to verify the repair, and the vehicle can be reassembled and delivered to the customer.

We recommend using replacement crash sensors directly from the manufacture. This will ensure the part is correct, and that the part will be up to date with all design changes and improvements. Also, if a crash sensor has failed due to corrosion, the other crash sensors, especially in the same area of the vehicle, should be inspected for corrosion or rust as well, and replaced if necessary.

It is extremely important that anyone servicing the SRS system, especially when servicing the components related to the airbags, has an excellent understanding of the system for that particular vehicle, and exercises all forms of caution and proper practice to minimize the risk of injury to persons or damage to the vehicle. The crash sensors main job is to cause the airbags to deploy, so any incorrect handling of the crash sensor or crash sensor circuit could potentially lead to the needless deployment of airbags and costs of repair.

Any portion of the SRS system is best left to a certified professional. Besides the risk of damage to the vehicle, airbags pose a great risk to personal safety if they are caused to deploy accidentally. Also, improper repairs of the SRS system can lead to the deactivation of airbags, which can result in exacerbation of injury in the event of a collision.