Why You Can’t Clear Airbag Codes After a Crash: Airbag Module Explained
About this video
How does a car airbag system actually know when to fire? In this video, an ASE certified mechanic explains how the airbag system works, what the airbag control module does, what happens inside it during a crash, and why the airbag light stays on and the codes will not clear after an accident. We also open up an airbag module so you can see the circuit board, the crash sensor, and the parts that store the crash data.
The airbag module goes by many names depending on the make: airbag control module (ACM), SRS module, restraint control module (RCM) on Ford, sensing and diagnostic module (SDM) on GM, and occupant restraint controller (ORC) on Chrysler, Dodge, Jeep, and Ram. This is a general guide that applies to nearly every make and model, including Toyota, Honda, Ford, Chevrolet, GMC, Dodge, Jeep, Chrysler, Ram, Nissan, Hyundai, Kia, Subaru, Mazda, Volkswagen, Audi, BMW, Mercedes-Benz, Lexus, and Acura.
SAFETY FIRST
Airbags and seat belt pretensioners are explosive devices. Disconnect the battery and wait the time listed in the service manual before touching any airbag component, because the module stores energy and can still fire an airbag with the battery off. Never probe an airbag connector with a test light or meter, carry a live airbag with the trim facing away from your body, and set it down face up.
WHAT WE COVER
The parts of the SRS system: airbag module, front and side impact sensors, driver and passenger airbags, side and curtain airbags, knee airbags, seat belt pretensioners, clock spring, and the passenger seat occupant sensor
Where the airbag module is usually mounted and why its position in the car matters
What is inside the module: the accelerometer crash sensor, the processor, the backup energy capacitors, and the memory chip that stores crash data
How the module decides in milliseconds whether a crash is severe enough to deploy, and which airbags to fire
Why the passenger airbag can be turned off automatically for a child or an empty seat
How the module constantly monitors every airbag circuit and turns on the light when something is wrong
What happens during an accident, including crash data and event data recorder information being saved
Why you cannot clear airbag codes after a crash, and why the module has to be reset or replaced after a deployment
Why some modules lock with crash data even when the airbags did not deploy
WHY THE AIRBAG LIGHT COMES ON
Stored crash data in the module after an accident
Bad clock spring behind the steering wheel
Loose or corroded connectors under the front seats
Faulty passenger seat occupant classification sensor
Seat belt buckle switch or pretensioner fault
Failed front or side impact sensor
Water damage to a floor mounted airbag module
Low battery voltage or a recent battery disconnect
Aftermarket seats, steering wheels, or an airbag unplugged with the key on
RELATED FAULT CODES AND WARNING MESSAGES
Driver and passenger airbag deployment loop codes such as B0001 and B0012, side airbag and side sensor codes in the B0020 and B0090 range, B0081 for the passenger seat occupant sensor, B0051 deployment commanded or crash data stored, and U0151 lost communication with the restraints control module. Depending on the vehicle, you may also see a Service Air Bag, SRS Malfunction, or Passenger Airbag Off message on the dash. A scan tool that can read the SRS module is needed to see these codes, because a basic OBD2 code reader will not show them.
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