Airbags power, is it battery

My car is a 2002 XJR and I’m planning to work on the Clock Spring for which I need to remove the driver’s airbag.
All the airbag removal instructions that I’ve read tell you to disconnect the battery for several minutes or up to an hour before doing work on airbags. Well, I’m looking at the electrical diagram 18-1 of the Jaguar 2001-2002 Electrical Guide that shows the car’s various airbags connected to the Airbag Single Point Sensor Module. The diagram shows only two leads coming out of each airbag and going to the single point sensor module and those two wires are the only airbag connection to anywhere in the car. Furthermore, the only power source shown on this diagram shows it coming from the ignition switch to the single point sensor module; no other power source. There is no battery connection shown on this airbags diagram. If this is correct, what’s, then, the deal with disconnecting the battery to work on a device that shows no use of battery power?

Would anybody know of another possible power source to the airbags, or any other connections that this guide is not showing?

Thank you!

Well, maybe I just read a confirmation to my initial post, it says:

“The system is only active when the ignition is on and for approximately 1 minute after the ignition is switched off”.
This pretty much explains that the airbag doesn’t care whether the battery is connected to the car or not because it only uses ignition power. Now, this text is from the “Technical Guide for the XJ V8 series introductory year, 1998”, which shows in words what the above mentioned 2001-2002 Electrical Guide showed on its electrical diagram.

Unless some member has additional info on the subject, I think that I’ll trust the guides.

See, the thing is that, lately, I have had just too much trouble in this car with Engine Lights and with the emissions circuits not getting ready for test for a looong time after the battery has been disconnected.
I’ll just keep the battery fully charged and connected.


Hi Reinaldo,
You are right, the battery is not directly connected to the airbags or seat pretensioners. Their power comes from the sensor module you mentioned. The module has internal capacitors for energy storage and will retain that power for some time after the key is off. That’s why the guide says to wait after turning the key off before working on the car. Even if the sensor is depleted and the key is off, there is a risk working near an airbag with vehicle power still connected. The amount of power required to deploy an airbag is relatively small, an accidental spark near the connector could be enough. So I recommend disconnecting the battery to prevent any chance of a spark happening around the airbag. I used to design these systems and although they are engineered to be safe I would never work around a pyrotechnic device with power connected.



Thanks, Richard,
Well, against better judgement, I did not disconnect the battery. I waited over night after switching the ignition off before doing work on the steering wheel. So, next day I carefully removed the airbag’s two steering wheel screws, carefully sled it around and carefully unplugged the 2-wire connector, then placed the airbag on top of the car’s roof. But I must confess that this time I was tense, even after the technical guide’s instruction that the system is not active from a minute after turning the ignition off. I was thinking that, maybe one should wear a catcher’s mask to do this protecting your face… LOL. And again, all this because of the pains I went through the last time the smog was due on this car and I won’t even mention the super ugly invoice that I paid after no less than 4 months in the shop. And all because I disconnected the battery a couple of months before the smog was due. Well, it will now be due again in about five months.