Ignition: On/Off at Battery Ground Connection

Hello.

I had to remove the airbag from the steering wheel during a repair and disconnected the ground cable from the battery in the process. Now, after everything was reassembled, the airbag warning light is on. I checked the wiring again, but I couldn't find any errors.
I just read in my 'How to work on your car' guide that you should turn on the ignition and then connect the ground cable to the battery. However, two pages later, it says that you should definitely turn off the ignition because connecting the battery while the ignition is on can cause damage to the fuel injection pump.
What is true? Could this solve my airbag problem?

Hi,

The first two suggestions involving the ignition system seem a bit strange to me; I can neither confirm nor deny them.

Based on experience, the airbag warning light will remain illuminated as long as there are error codes stored in the airbag control unit.
"With my A3, I also couldn't detect any 'lost cycle' behavior, meaning I had to clear the error codes to get the warning light to go off (I have a cable or connector problem with my side airbag, so the control unit complains about excessive resistance every few months, but I haven't been able to locate the source of the problem yet)."

Best regards, Rainer.

In the VW installation instructions for the GRA lever (which requires removing the airbag), it is clearly stated that the battery must be disconnected.

If you have the ignition on and then reconnect something, you'll only get massive voltage spikes throughout the entire electronics system – I can only describe doing it that way as utter nonsense.

Okay, turn EVERYTHING off when you reattach them.

But why should only I be a victim of these great "do-it-yourself" books? Because of unclear and incomplete descriptions, I damaged a camshaft when working on my car at the Japanese parts store!
So, it's definitely learning by doing .

m;

With my A3, I also couldn't detect any 'lost cycle' here, which means I had to clear the error memory to get the light to go out .


This is a requirement because the airbag is a safety-critical component. Any, even the smallest, intermittent fault MUST be permanently stored and displayed.

CU Gremlin.

Hmm, so opinions are now divided!

I can only say what my friendly acquaintance told me!

Turn the ignition on first, then connect the battery, and the airbag light will not illuminate.

What's the truth? Who did it?

I had my steering wheel, including the airbag, removed twice.

1.) Connecting to the battery without turning on the ignition: Error message?

2.) With the ignition on and the battery connected: no error messages?

What's right now?

The instructions in the GRA guidelines sometimes say one thing, and sometimes another, depending on which version you find.

I have an A4 with a 66kW TDI engine, manufactured in June 1999.

EDIT: Of course, the battery must be disconnected before and during installation, but what about after that?

Okay... the thing about turning the ignition on and then connecting the battery is just a safety measure to ensure that the person isn't sitting in the car when they're connecting something to the airbag, for example, on the steering wheel. If the ignition is on and they're connecting something, they're definitely outside of the airbag's deployment range.

Disconnect the battery and only reconnect it when everything is correctly assembled. Always turn off the ignition to avoid harmful voltage spikes.

Incorrect entries can be deleted. (End of transmission)
0 EUR

"Blown" engine control units (ECUs) can be purchased new. (Ignition on)
900 EUR


You have the free choice .

I agree with Julian.

The battery clamp with the ignition switched on is certainly only for your own safety. Because when you connect the battery, you are not behind the wheel and therefore outside of any danger in case the airbag should deploy.

However, this can actually damage the electronics because connecting the battery with the ignition on already creates a high current demand. The problem is that you don't immediately get a verschandeln connection, but instead, the sparks cause rapid current surges (and, due to di/dt, also large voltage spikes), leading to abrupt on/off cycles for the electronics.

I would prefer to connect the battery without the ignition being turned on, and then turn on the ignition from a non-airbag-sensitive area, preferably several times for testing purposes.


Best regards, Georg.

Quote:

I would prefer to connect the battery without engaging the ignition, and then turn on the ignition from the passenger side, ideally several times for testing purposes.

Well, I might prefer to reach in from the outside, between the speedometer and the steering wheel.

Because if the driver's airbag is already deploying, why shouldn't the passenger airbag also deploy?

And it's a bit bigger, and then it shoots me and spins me before throwing me onto the passenger seat!

The advantage of "from the outside" is also a slightly reduced risk of concussion, as the air pressure from the ignition inside is significantly greater than outside (I can provide information on concussion risks ).

I would even wear hearing protection the first time I ignite it.

m;

You are absolutely right dieselmartin.

If the vehicle has 2 or even more airbags, one should approach the situation with even greater caution.
Hearing protection is even more important in this case, because the pressure wave is extremely strong.
In my opinion, the airbags are not connected in parallel, which means the risk only comes from the 'repaired/reconnected' airbag. However, it cannot be ruled out that feedback (e.g., due to incorrect wiring) is being sent to the airbag control unit.

But safety is safety!!!

Lower all the windows, and either stay outside in front of the steering wheel and turn on the ignition, or lie down on the front seats and fiddle with the ignition.

Okay, I was already thinking about the DAU (Daily Active Users) thing. And also about the voltage spikes.

We are well aware of that too.

After seeing everything I've seen at the Audi workshop, I believe there are definitely a few 'DAU's (people who are clueless) working there.

So, we're constantly disconnecting batteries whenever we're working in the engine compartment or doing something with the electrical system...

It's always disconnected by turning the ignition off, and the airbag light has never come on afterwards.

Connecting devices when the ignition is on is absolutely not recommended. Almost all control units receive power through terminal 15, and connecting devices this way can cause sparks and damage everything.

Before disconnecting the airbag, it's important to allow the control unit to discharge its capacitors. Only when everything is fully discharged can the control unit stop performing loop measurements. This will prevent error messages. And, of course, everything must be 100% in order before reconnecting the battery, otherwise the warning light will illuminate.

CU Gremlin.

So,

The problem was that the control module behind the ignition switch was defective, which meant I couldn't start the car. After finally managing to remove the steering column housing, I installed a new control module and tried to start the car again, without connecting the rest of the components (turn signal switch, wiper switch, and AIRBAG).
The car started right away, but I didn't even notice the airbag warning light. Probably, the lack of connection to the airbag system will now be registered as an error, and I'll have to have the error codes cleared.

It also seemed very strange to me that it happened with the ignition on, but I don't know the tricks of the wiring techniques, so I just wanted to ask about it.
Ultimately, clearing the error memory should resolve the issue, right?

Thank you for your previous responses.

Hello!
Nice discussion... So, about connecting the battery with the ignition on: absolutely not! You might be able to do that with a Golf I with a carburetor engine, but in our cars, the wiring is different. The voltage spikes will break anything that feels like breaking. Our apprentice connected the battery with the ignition on while working on his BMW E 39, and it fried the navigation system... He had to replace the display and the control unit; he was really unhappy.
Airbag/seatbelt pretensioner control units are designed, as Gremlin mentioned, in such a way that the warning light will only turn off after the error memory has been cleared, even after the fault has been resolved. However, this does not prevent the airbag from deploying. The capacitors in the control unit will charge regardless of whether the ignition is on, unless the control unit is defective. Furthermore, above a certain impact energy, it doesn't matter whether the seats are occupied or not, and whether there is an error code stored or not; the control unit will attempt to trigger the airbag. In other words, even if the warning light is on, all safety precautions must be taken when installing or removing airbags/seatbelt pretensioners. And turning the ignition on with a missing airbag... what more could happen?

Best regards,

Dominique.

It can happen that the ignition is turned on without the airbag system functioning, for example, if someone is fiddling with the seat heater and forgets that there's also an airbag system involved. (-> The airbag warning light comes on and stays on).

And as with my previous speakers: ALWAYS turn off the ignition when connecting or disconnecting the ground cable. Normally, the airbag light will not illuminate after reconnecting.

Best regards, R. Mark.

Hm, the airbags and the control units seem quite tolerant regarding all of this. As the Gremlin would say: 'Luckily, the airbags don't know what we're writing here.' I'm turning off the ignition and disconnecting the airbag, then I'm swapping my steering wheel and reattaching the airbag. After that, I'll turn the ignition back on (forgot to install the airbag last time *g*, the warning light was obvious) and nothing will explode. Why would it? Everything is connected correctly, and if it's not, then nothing will happen. It has no connection. It's different if you're electrically charged.

I once had an accident in a vehicle that had driver and passenger airbags, as well as pyrotechnic seatbelt pretensioners. The airbags deployed, but it wasn't actually very loud. Those firecrackers people set off on New Year's Eve are louder.

Best regards, WarLord.