Pressure sensors — what are they, where are they, and why are they one-time-use parts?

In a recent “Airing of Grieveances” episode from Nylund’s Collision Center, owner Rob Grieve shared that pressure sensors could mean life or death in a collision.

Pressure sensors are responsible for the timely deployment of air bags. Sensors can be found in vehicle pillars and doors.

For example, a peripheral pressure sensor located inside the front door actuates curtain air bags. Grieve noted that, unlike the front and back of the vehicle, the sides have limited crumple zones.

To ensure enough time for the restraint system to respond following an impact, the air bag control unit must decide in less than 5 milliseconds whether a deployment is required based on the type and severity of the crash, Grieve said, reading from an OEM repair procedure. Peripheral pressure sensors work off of a door collapsing and building up pressure in the door.

Grieve relayed to the audience that Toyota says to remove pressure sensors when blowing dust off the vehicle with an air blower because it can cause the air bag to deploy, causing serious injuries or death.

Nylund’s Collision checked with a Subaru dealership that runs a wholesale parts business to see how many pressure sensors they’ve sold recently to get an idea of how often local shops in Colorado replace them. They were told three had been sold in the last two years whereas at least two replacement doors have been sold every month in the last three years.

“What does that mean to you, the consumer? It means either there’s an incredible lack of knowledge out there of what needs to be done to keep you and your family safe on the repair side of things — the shop that you choose to bring it to,” Grieve said. “Or it could be, potentially, insurers saying that’s not necessary because they would look at what we read there [in OEM procedures] and they would say, ‘Well, that’s just a recommendation and we don’t feel like that needs to be done.’ And many shops would say, ‘Oh, OK.’

“Air bags have become more and more complex and the science that is going into them has become rigorous. That system thinks faster, with all the information those monitors are getting, than we can think. That’s why there’s no switch to just hit the button for air bag because you think you need them. The car knows. It’s important, to you — a consumer — that you’re taking it to someplace that will do the research necessary.”

It’s necessary to look up OEM procedures for every single vehicle in every repair because not every model’s parts and repair requirements are the same, and procedures change often.

“This stuff is all there to operate as designed and keep us safe,” Grieve said. “If it’s off a few milliseconds, that could make a big difference.”

Procedures should also be checked for every job, even paintless dent repair. In the case of BMW models, which can carry pressure sensors inside the cavity of side doors, to ensure the sensor works properly holes can’t be made on the sides of a door because it wouldn’t otherwise allow for the door to be sealed as it was from the factory. This isn’t uncommon for other makes and models as well. And the use of incorrect, seal-less clips could mean a big difference in air bag deployment timing.

It’s also possible that OEMs can call a part reusable and then change it to one-time-use or vice versa and those changes wouldn’t immediately be captured by estimating systems, and would only be found in accessing the current repair procedure from the automaker, at the time of repair.

In a 2018 webinar about the Toyota Technical Information System (TIS) website, Collision Advice CEO Mike Anderson alluded to a Toyota part that began as a one-time-use, and later it received clips allowing it to be reusable.

Examples provided by Database Enhancement Gateway (DEG) show similar OEM procedures from Tesla, Subaru, and Kia.

For 2012-2020 Tesla Model S vehicles, the OEM states in its service manual: “Inspect the Pedestrian Protection pressure sensor tube and connector for signs of damage, such as tears in the tube and cracks in the connector. Replace the pressure sensor assembly if any part has been damaged.”

Tesla points out the importance of proper sealing near sensors as well.

“Always replace any plugs or tape removed from the front door shells when replacing a front door pressure sensor. Additional holes in the door create more escape paths for air, which decreases the sensor’s ability to detect a side impact, and can negatively affect airbag deployment.”

There are also conditions of damage in which the knee air bag assembly and steering column need to be replaced.

According to the manual, the following should be replaced along with all accompanying fasteners after an air bag is deployed in addition to parts that should be replaced after a seat belt pre-tensioner is deployed:

• • Any deployed air bag and all accompanying fasteners
  • Steering wheel assembly (if the driver’s front air bag deployed)
  • First-row seat assembly that contains the deployed airbag (if a side seat mounted air bag deployed)

A repair procedure for the 2024 Subaru Outback states that when a front door side impact sensor is removed it should always be replaced with a new part.

“If it is reused, sealing capability on the contacting surface of door panel may be insufficient and impact pressure may not be detected correctly,” the procedure states.

The procedure notes that nuts can’t be removed from the sensor, and if they are removed with excessive force, deformation of the front door panel assembly can occur. Damaged clips are also to be replaced with new clips.

For the 2023 Kia Carnival, an OEM procedure states that the door module must not be “transformed,” or damaged, because the Supplemental Restraints System Control Module (SRSCM) determines impact through the pressure sensor in the door module.

“There is a chance to have some problem with durability and decline performance of detecting collision if the door module installed area has been damaged,” the procedure states.

According to Bosch — which DEG says makes peripheral pressure sensors for Mercedes-Benz — two or four peripheral pressure sensors are connected to the air bag control unit alongside the peripheral acceleration sensors (PAS) on the supporting structural components, depending on the type of vehicle.

I-CAR also provides links to various OEM procedures on one-time-use parts and fasteners here.

Editor’s note: This article has been updated to add sensor location information.

Images

Featured image of pressure sensor provided by Repairer Driven News reader. 

Photo of pressure sensor on door taken from Nylund’s Collision Center “Airing of Grieveances” YouTube video.