Get to Know Your Vehicle’s Occupant Classification System

Most modern vehicles are equipped with multiple advanced systems designed to keep passengers safe and minimize serious injury in the event of a crash or major collision.

One example is the occupant classification system, which is responsible for airbag deployment and passenger detection.

What Is an Occupant Classification System (OCS)?

An occupant classification system (OCS) is a group of sensors that helps determine whether or not the passenger-side airbag should be deployed.

Also known as the occupant detection system (ODS) or passenger presence system (PPS), the OCS relies on the weight on the seat and whether or not the seat belt is fastened to determine if the airbag should deploy or remain disabled.

According to the US Federal Motor Vehicle Safety Standard 208 (FMVSS), the passenger-side airbag should deploy or remain disabled under four conditions:

• The passenger-side airbag should not deploy when there’s no weight on the seat and the seat belt isn’t fastened. The passenger airbag light should also be turned off.
• A weight range of about 10 to 37 lbs should keep the airbag disabled, as this typically represents the weight of a seated child.
• A weight range of about 38 to 99 lbs is enough to deploy the airbag but only at a reduced force. This weight range typically represents a child or small adult.
• The passenger-side airbag will deploy at full force if the detected weight is 99 lbs. or more. Airbag deployment will depend on the severity of the crash, vehicle speed, and other factors.

Occupant classification systems have been around since the early 2000’s as part of supplemental restraint systems.

But before they became a standard feature on most modern vehicles, airbag deployment was quite aggressive and easily triggered, putting children and small passengers at risk of getting injured.

To prevent airbag-related injuries, the US Department of Transportation ordered that vehicles made after 2006 should reduce such casualties, hence the development of occupant classification systems.

Types of Occupant Classification System (OCS) Seat Sensors

An occupant detection system consists of several sensors that usually fall under the following types.

Gel-Filled Bladder Sensor

A gel-filled bladder sensor is a silicone-filled bag with a pressure sensor attached to it. The pressure sensor is responsible for measuring passenger weight. It also sends a voltage signal to the control module responsible for deploying the airbag.

To determine whether or not the seat belt is restraining a child, the sensor is also accompanied by a safety belt tension sensor.

Capacitive Strip Sensors

Capacitive strip sensors use conductive metal strips under the seat cushion. These strips transmit and receive a low-level electric field that changes depending on the weight of the occupant in the passenger seat.

Force-Sensing Resistor Sensors

This type of sensor changes in resistance, depending on the applied stress. The change in resistance allows the control module to determine the weight of the occupant.

Advantages and Limitations of Having an OCS

Occupant classification systems provide more seating options for their passengers. Some vehicles with an OCS permit automatic seat adjustment based on the presence or absence of occupants.

If a collision is strong enough to deploy the airbags and there is no occupant in the passenger seat other than a few items, the airbags won’t damage such objects.

Improved vehicle performance is another advantage of having a fully functional occupant classification system.

An OCS optimizes airbag deployment, which means they won’t get triggered under the slightest collision or impact.

As for its limitations, an OCS might not be as efficient under certain conditions. For example, sitting too close to the edge of the passenger seat might reduce the effectiveness of the OCS.

Seat types, such as bucket and bench seats, might also affect the performance of the occupant classification system.

Potential Issues Related to Occupant Classification Systems

While automakers and manufacturers make sure to run their tech under stringent testing procedures, there are times when certain functions fail, including OCS operation.

Supplemental restraint systems like the OCS might detect false positives and negatives, affecting its efficiency.

If the system detects a false positive, airbags might deploy even in the absence of a passenger. Meanwhile, a false negative might prevent the airbag from deploying, increasing the risk of casualties during a collision.

Diagnosing Occupant Detection Systems

Faults in the occupant detection system might cause the airbag light to turn on even when there’s no passenger.

Under this circumstance, it’s important to have your vehicle checked for trouble codes immediately, as airbag deployment is crucial in reducing casualties during a crash.

A scan tool is usually used to diagnose OCS issues as well as faults in other systems.

ODS sensors might require calibration to get them working as they should. This process typically requires professional assistance, especially for those with limited knowledge about auto repair and systems diagnosis.

As a car owner, it’s your responsibility to stay on top of your vehicle’s maintenance schedule to resolve minor issues before they escalate into something much bigger (and more costly).