Repairing Occupant Classification Sensors

Occupant Classification Sensors airbags supplemental restraint systems

Occupant classification sensors (OCS) are a relatively new addition to vehicle safety systems. They all provide the same function but do not all operate the same. Because of the design and the way they perform their jobs, each manufacturer has a different set of repair guidelines to follow for specific situations. Here are some steps to help you both understand how these sensors work and determine the best methods to repair them.

STEP 1: UNDERSTAND OCS BASICS. OCS determine the type of occupant (for example, adult or child) sitting in the passenger seat by examining a number of factors, such as passenger weight. The OCS then sends a signal to the restraints module to help determine the level of deployment for the passenger airbags. This process allows the safety restraint system (SRS) and the OCS to work together to best protect the passenger.

STEP 2: IDENTIFY THE OCS TYPE: There are many different OCS types. Some are incorporated in the tracks; others rest under the seat cover or pad. The track type usually has four sensors, one in each corner of the track. These sensors read the pressure applied from all four corners.

One type of sensor features a gel-filled bladder. When the occupant sits in the seat, the gel is displaced, and the sensor monitors the amount displaced. This sensor type often is overlooked because it is not as obvious as track sensors. Keep in mind that many vehicles have OCS modules mounted under the seat.

The third OCS type is a seat mat that senses the occupant's weight. OCS types vary from model to model.

STEP 3: RECOGNIZE THE REPAIR ISSUES ASSOCIATED WITH EACH OCS TYPE. When repairing vehicles with sensors incorporated in the track, modifying the seat in any way will change what each sensor reads. Note that during the calibration process, you will re-zero the seat to give it a starting position. If you change the value that the seat recognizes as the defined weight, you will change the way the seat does its job. Any bending and flexing of the seat and floor can similarly change how this sensor performs.

A track sensor can be affected if there is too much debris stuffed under the seat, since this debris puts pressure on the seat frame and tracks. Items like water bottles or soda cans may get wedged in or under the tracks and help create false readings. Too many items under the seat can pull on wiring and connectors to disable the system.

Items like monitors, strap-on bags, and various other things attached to the headrest or back of the seat can throw off the OCS incorporated into seats. This added weight at a high point in the seat adds leverage to the seat back. This increases pressure on the sensors.

Changes to the seat also can affect the functioning of sensors with gel-filled bladders. This type of sensor can be affected if the seat is removed or disassembled.

Sensors located in the seat mat are subject to environmental variables like heat, density and electrical fields. The Honda/Acura mat sensor has been known to give false readings if an aftermarket seat heater is installed over the top of the sensor. Mercedes-Benz has released technical service bulletins (TSB) warning that setting a laptop or cell phone on the passenger seat may provide false readings to the vehicle computer. Anytime you deal with this type of sensor it is never a good idea to change the way the seat is constructed or add something to the sensor or seating area.

STEP 4: FOLLOW THE OEM REPAIR GUIDELINES TO THE LETTER. OEM guidelines feature a wide range of steps and procedures that must be followed to ensure proper OCS repair. Some require calibrating the OCS if the seat is removed and others if the system is repaired or replaced. Some automakers (for example, Toyota/Lexus) have a much more defined set of requirements.

The information needed to repair these systems can be difficult to find, but it is available. You'll need it both to identify the type of sensor you are dealing with and to understand where the OCS are located so as not to damage them in the repair process.

When the recommendations are not followed, you run the risk of putting your customer in grave danger due to the SRS not working correctly. Don't be fooled by the airbag light. It can appear to indicate a properly functioning SRS even when the proper procedures were not implemented and problems remain with the OCS. The OCS functions within specific set parameters, leaving little margin for error.

STEP 5: BE AWARE OF ALL REPAIR ISSUES SURROUNDING THE OCS AND SRS. Requirements for handling the different types of OCS can vary every time a vehicle is brought in for repairs based on the collision damage and other factors such as whether the seat was removed or the seat cover or any part of the OCS was ever repaired or replaced.

Be careful when replacing both the OCS and the SRS modules at the same time in a Chrysler product. Doing so can produce a permanent trouble code that only a Chrysler dealer can fix.

Be careful handling the seats. Dropping them can damage the sensors, which are expensive to replace. Toyota, in some cases, will require you to replace the entire seat at a cost of more than $4,000.

The process of calibrating the OCS requires the use of a factory scan tool and, in some cases, weights. Some manufacturers, such as Chrysler, require multiple weights used in various intervals during the calibration process. You may need to test drive the vehicle. Honda recommends driving the vehicle after adding weight to the seat.

Each manufacturer has a specific procedure and scan tool for the brand to accomplish this task. Scan tools may need to be updated to cover the year and model that you are working on.

Be wary of employing salvaged OCS parts since there can be many things wrong with them. They may have water damage, or may have been mishandled, dropped, or simply bent in a collision. Many, if not all, insurance companies have policies about using airbags and sensors.

STEP 6: LIABILITY QUESTIONS. Since you assume liability for the repair, you need to make sure anyone else involved with OCS repairs (the insurance company, dealer or airbag repair service) realizes that these repairs always must be performed according to manufacturer recommendations.

Repairing the OCS all comes down to awareness, along with possessing and using the knowledge of how to properly handle these repairs – doing what is best for the vehicle owner, in this case, ensuring the vehicle will properly protect its occupants as it was intended.