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Discussion Starter · #1 ·
I have now resolved my airbag light issue. I have major beef with cars these days (rant alert!). These days cars are so stuffed with electronics that it’s back to dealer for a faulty cigarette lighter (or Aux 12V Power as they’re now known). However, my beef isn’t that cars are stuffed full of electronics, it’s that a main dealer DOES NOT KNOW HOW TO REPAIR ELECTRONICS. Instead, the approach is modular. Last year Mini ‘fixed’ my ABS issue in a modular way. Changed ABS ECU (£1,200). That showed up another issue so changed yaw sensor (£600) and on it went until they'd cleared all the error codes. By this time they have swapped out what in reality is £50 of electronics that costs the customer £2,000. The ACTUAL fault will be as trivial as a 3p ESD protection diode somewhere inside an ECU, but it's not cost effective to spend the time fault-finding at the component-level. Rant over.

So, now that I’ve solved my airbag issue, I want to share as much information as possible in the hope it’ll stop someone out there spending silly money fixing a basic fault.

My problem: One day suddenly had red airbag light and red seat belt light permanently on. I had an open-ended quote from main dealer to fix this. They suspected a few things and estimated cost of repair to be between £400 and £2,000. Ouch. really didn't want to go to garage, so here's what I did...

First thing I did was buy an OBD code reader on ebay that could read the Mini R57 codes (the VERY cheap code readers that use your iPhone don’t seem to support Mini/BMW codes so make sure you get one that can). The one I bought is called a C110+ and cost me £29.

I plugged this into the OBD port (above accelerator pedal) and scanned the car. Airbag unit reported two issues:


I decided the airbag ECU had died and I needed another (based on the phrase 'internal fault'). I hit ebay and found a million similar but none with exactly the same number. However, I noticed that the one in my car was not original (its year of manufacture was six years after my car was made) and so bought one ‘typical’ of my R57’s year of manufacture (£20 on ebay). I was told that it would need coding to the car so I did expect that at some point I’d have to involve a BMW garage.


I fitted this ECU (under the handbrake, see for good videos of how to replace this) and re-read the codes. This cleared one code (the code that indicated a comms fault in the ECU) but it did not clear the airbag code.


So, I assumed all was well with the new ECU and set about fault finding the airbag code. I removed the airbag from the steering wheel and checked the pins for corrosion, there was none. Next, I added a 3.9 Ohm resistor across the airbag connector pins in the steering wheel. If the airbag unit was faulty then I was hoping this would ‘trick’ the ECU into thinking there was a good airbag installed. This made no difference so I assumed airbag was good. To my mind this left the wiring harness and the steering column. The steering column has a single unit that includes all controls (indicator stalks, audio controls, wipers, etc) and it has an integral ‘clock spring’ that allows the airbag, horn and steering wheel switches to work whilst the wheel is rotated. I stripped down the steering column so that I could test airbag connectivity between steering wheel side and rear side of this unit. I didn’t need to reach for my multi-meter. As soon as I removed the steering wheel I could see the clock spring had self-destructed. The ribbon cable inside it had torn and it was destroyed.



I tried to find an exact replacement on ebay. It’s a minefield! Nearly all ‘R57’ ones on ebay were absolutely NOT from R57s as they had rear window washer controls (R57 is soft-top and does not have rear window washer). Some did look identical, but had different part numbers. One thing that I did notice was that the front half of the assembly (the clock spring) looked identical on all part numbers so rather than keep searching for the exact part (3451905-01) I decided to buy the cheapest one I could find and use just the clock spring. This also has the advantage that I keep my electronics so there should be no issue with software and coding to the car.

The one I bought was £25, free P&P. Whilst waiting for the unit to arrive I had a probe around with my multi-meter to make sure the airbag signals did not disappear into the steering electronics. Here is what I found:

6-way connector behind steering column is pinned-out as follows:

2 - airbag
4 - airbag
5 - horn
6 - horn

This plugs into the back of the comms unit and passes through the clock spring to the connector visible under the driver’s airbag. Here it is pinned-out as follows:

1 - airbag
2 - airbag
5 - horn
6 - horn

The clock spring unit removed from £25 ebay squib.


The position the encoder wheel needs to be in when you fit the clock spring (note the two holes at nearly 4 and 6 o'clock)

After fitting, error codes gone:

First time I've seen no lights for a long time.


Code reader: £29
Airbag ECU: £20
Squib: £25

This has cost me £74 and a load of time faffing. Well worth it in my opinion.

Top tip though, and I wish someone had suggested this - try your horn!!! If your clock spring is as wrecked as mine then your horn won't work either.

If you have a similar issue, hope this helps.

Final thought: during this saga I found people on youtube suggesting you 'buz out' your airbag to check it's resistance. DO NOT DO THIS! Resistance meters work by injecting a voltage. If that sets off the air bag, you could be killed (and if that sounds OTT check out people setting off loose airbags in parks on youtube!)


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