The most common problems that cause airbag light and restraint system malfunction warnings on a BMW are low battery voltage or faulty passenger occupancy sensor (mounted under the passenger seat).
This guide will show you how to identify and fix common malfunctions in restraint systems.
Symptoms
Most BMW owners will get one of these warnings when there is a problem with the airbags and restraint system.
- The airbag light stays on
- Driver Restraint System Malfunction error
- Passenger restraint system malfunction warning.
- Restraint System Faulty
- Pass. Restraint System fault on the dashboard
Get your BMW diagnosed as soon as possible and continue to wear the seat belt.
Common Problems
Common problems that trigger BMW restraint system malfunction.
- Fault in the airbag module
- Defective seat belt tensioner
- Belt force limiter
- Low battery voltage
- Defective clock spring
- Passenger occupancy sensor
- Wire harness
- Water damage
Airbags
Airbags are a restraint device, which deploys only during a severe collision.
There are three types of airbags depending on the model: side, curtain, and front. The front airbags can be found on the steering wheel as well as the dashboard at the passenger’s side.
They are activated during a frontal collision to reduce head and chest injuries. Side airbags, which are found in the front seats, protect passengers from vehicle rollovers or side impacts.
Curtain airbags play a similar role to side airbags, and help reduce injury from broken glass. These airbags can be found between the A- and C pillars.
An airbag that has been previously deployed will cause the warning light to flash if it is not in good condition. The wire harnesses connecting to the airbags are a much more common problem. The wires connecting to an airbag’s interior can be damaged by minor accidents or previous.
Airbag / SRS Module
Supplemental Restraint System (SRS) module, also known as airbag module, controls the restraint system. It uses impact sensors in order to determine the severity and extent of a collision.
It takes about 20 milliseconds to take action if the system detects sufficient acceleration. The control module might deploy seatbelt pretensioners only if the impact force is low. It may also display malfunctioning restraint system on the dashboard.
Airbags will deploy at the same time if the impact force exceeds a certain level. The signal causes a chemical reaction that produces rapid expansion of nitrogen gas. This inflates the airbag in about 30 milliseconds.
Passenger Occupancy Sensor
Besides these features, most BMWs from 2003 onwards have a system that monitors when a passenger is on the seat and their weight.
This is the most frequent failure point.
The sensor is actually an electrical mat that is installed at the base of the passenger’s seat. It carries the entire weight of the passenger and can often fail over time. It can start out as an intermittent issue, and then it gets worse over time.
Emulators are available to solve the problem but they make the passenger airbag activated all the time. It is time-consuming, expensive, and the best way to fix the problem is to replace it.
Battery Safety Terminal (BST)
Cars with a battery safety terminal, or BST system, can have an issue with a damaged BTS cable.
This happens most often during a battery change, and can cause a malfunction in a restraint device.
Follow this guide to learn how to replace the BMW BST terminal.
Connector / Wire harness
Another possible issue is a loose or broken seat connector.
They can be found on both the driver and passenger side.
They can be easily damaged if foreign objects are pushed under the seats, especially if they are moved frequently.
Other components like airbags and seatbelt tensioners rarely fail by themselves. They can be activated or damaged during assembly and disassembly, if they aren’t handled correctly.
Seat Belt
Seat belts prevent sudden forward movements and ensure passengers are in the correct position for airbag deployment.
Seat belts come with pre-tensioners that tighten the belt across the passenger’s chest and lap to prevent forward motion.
The load limiter reduces the pressure on the chest by allowing the seatbelt tensions to relax in a controlled fashion.
How to Diagnose BMW Restraint System
Below you will find instructions on how to read fault codes from the BMW SRS module. For this procedure, you will need a BMW scanner.
- Park your BMW and set the parking brakes.
- Locate the diagnostic port beneath the dashboard.
- Turn on the ignition but not the engine. Turn on the scanner, and let it communicate with the vehicle.
- Select BMW from the main menu, then your particular model.
- Select Control Units next Select SRS Airbag Module
- Select Read Fault Codes. To learn more, watch the video below.
Restraint System Warning Messages
This is a list of warning messages that may display on the dashboard.
- Driver restraint system malfunction. Continue wearing a safety belt. Check with the nearest service centre.
- Passenger restraint system. Fault in the belt tensioner, airbag or belt force limiter. Wear a safety belt.
- Pass. Restraint Pass. Fault in a passenger restraint device can affect airbags.
- Drive carefully to the nearest service center. The passenger restraint system is limited—an increased risk of injury in case of a collision. Continue wearing your safety belt.
- Pass Restraint System – Fault in passenger restraint system affecting airbag, belt tensioner or belt force limiter. Continue to wear your safety belt.
- Passenger restrains systemContinue wearing the safety belt. Malfunction. Continue to wear your safety belt. Seek out the nearest service center.
