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mercedes airbag system fault

Mercedes Airbag System Fault

When you buy your dream car, you no doubt consider style, comfort, performance and value.  And then after that, you might consider safety.  We generally just accept that the car has all the safety spec as standard and move on from there.  And that’s why, sometimes we need to know our car is in safe hands with our garage of choice.  

And with client safety being our priority here at Garden City Garage, our Mercedes specialist technicians ensure all client vehicles receive the benefit of our years of knowledge and expertise. And that they are fixed with the care and attention that every vehicle deserves.

As the local Mercedes service and repair garage covering Swansea and the surrounding areas, we use our 20 years of experience to ensure that all our clients receive their first-time fix every time. Using our unique 15 step diagnostic evaluation process means that our Mercedes technicians can get to the root cause of the problem. This ensures that we do not have to replace unnecessary parts, giving our clients the peace of mind that their car is in safe hands. 

Mercedes Benz expertise at local garage prices.


Mr W brought his Mercedes C220 AMG to our Neath based garage and told us that he had been experiencing a fault with the bonnet and airbag system.  

With the car in our presence, we checked the warning light and could confirm that the bonnet open warning light was on, as was the airbag warning. With a visual inspection, our team confirmed that even though the warning lights were present, the bonnet was, in fact, closed and secure.

mercedes airbag system fault

Using our knowledge and experience in Mercedes, our technicians immediately began to think it was a communication problem in the vehicle’s software. But rather than making assumptions, our team began investigating further by accessing the vehicle’s supply data.

Our Mercedes specialists accessed the car’s supply data, which allows us to signpost the fault correctly. The download gave us the error codes:

  • A207/B2207 Internal fault in the control unit
  • A761/C240300 Right front reversible emergency tensioning retractor
  • 520201/C120201 A1 instrument cluster is faulty
  • 520400/C120400 No message received from control unit central gateway

Knowing that the bonnet was shut and all switches registered as closed, our Mercedes Specialists turned their attention to the airbag access control module. The Airbag access control module is what controls airbag deployment. The control module receives information from the impact sensor during an accident then deploys the airbags if a collision is registered. So, if a fault is present within this module, it could potentially compromise the client’s safety.

Our team of Mercedes specialists stripped the airbag access control module and checked all power connections and groundings for the unit, checking for defects. With the team being able to confirm all links were working, we turned our attention to the module itself and could confirm that it was the module that was faulty and needed replacing.


As a local Mercedes Service and Repair specialist, Garden City Garage uses genuine and high quality Mercedes parts in all our repairs to ensure the integrity of our client’s Mercedes.

Our team of Mercedes specialists started by replacing the airbag control module, but this is where it got interesting. When we began coding the new module, it would not accept it as another fault was present. Another possible drawback that might have been overlooked by other garages who don’t specialise in Mercedes repairs and servicing.

Now we had a fault that wasn’t there before. We had to get to the bottom of it. Our Mercedes technicians confirmed that the old module wasn’t communicating correctly.  

Using our knowledge and experience, we were able to identify that the new fault was an issue with the pyrofuse, a fuse that can disconnect to avoid a short circuit or fire when the car gets into an accident or crash.

As Mercedes specialists, our team has access to Mercedes manufacturer wiring diagrams. With the help of the diagrams, our technicians located the pyrofuse and confirmed that it was broken.

Due to the location of the pyrofuse, it would appear it had been previously broken when someone had replaced the battery in the vehicle. The connector is located underneath the battery, so the break had gone undetected. A broken pyrofuse will signal to the access control module the car has been involved in an accident, and therefore the system thought that the airbag had been deployed, hence the airbag warning light.


With a pyrofuse connector repair kit sourced, our Mercedes specialists wired the new connector into the vehicle, which meant they could code the module and confirm that all were working with a complete retest.


With our knowledge and experience, we can give our clients the best servicing and repair results every time. Mercedes Specialist technicians can pinpoint the fault, source and replace the necessary parts and get the vehicle back to the client ASAP, and in the case of Mr W within three working days.  

This saved the client time and money and gave Mr W the peace of mind of a first-time fix.

Mr W was happy to receive his Mercedes C220 AMG back in working order, with all work completed, confirmed and at local garage prices.

If you would like to book in for your Mercedes Service with Garden City Garage, contact our team today on 01639 701604. We will get you booked in at a time convenient for you.  

You won’t regret it.

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