Car airbag diagnostic code reader.

[jimbo84]

I've got one of those cheap ebay engine code readers that works well but only does engine codes. The airbag light has come on on the better half's car. It happened during all the really wet weather so suspect it's water in a sensor or something similar but need to know where to start looking. It's a Hyundai i20, been looking for a cheap code reader/reset that will do the job but as per usual ebay/amazon are overflowing with chinese knock offs.

Anybody got a cheapish one (sub £100ideally) that works. There seems to be a lot of Autel ones around for £80/£90 but Autel themselves warn about grey imports and them being locked out to the Chinese language when updating, having to send back to china if they go faulty etc.etc. Ebay and amazon are becoming a bit of a nightmare now and almost unusable for trying to buy anything electronic.

 

[Barking Mat]

I only learnt the other day....

On my mates toyota, the air bags are set off by a sensor in the seat belt mechanism.

Hope this helps.

 

[Fazerruss]

Is it the air bag light or the srs light ( two different things). On some cars the srs will self reset if the problem is rectified.
Where up north are you? If you are close I can plug my reader in for you.

 

[jimbo84]

It's the one below that is on. Thank you for the kind offer but I'm a fair way from Yorkshire.

 

[premmington]

We have G-Scan3 here which is dealer spec for Hyundai/Kia. It is £2250 plus VAT - plus yearly updates.

Korean stuff is not easy to get knock/off - copy stuff for - this is why I had to resort to the proper tool for the job.

How close are you to Norfolk - I would plug it in and read it for you FOC.

 

[jimbo84]

Thank you @premmington very generous of you. I'm probably a good 5 hours or so from Norfolk though!

It looks like I'll be dropping into a local garage to get it read, there is a local one we use for MOT so I think I'll give them a try.

 

[jimbo84]

Got it read this morning. B1346 High resistance DAB. It seems that hyundai clock springs are a bit pants and this is the most likely culprit.

 

[jimbo84]

Clock spring pulled off. Measured the resistance of it... coming to 1 ohm, fluctuates by 0.02 of an ohm when turning, anybody any idea what they should measure? This was the measurement of the two cables combined using the grounding pin to short out the plug end.

Similarly anybody know what the resistance of an airbag should be? So I can replace the bag for a resistor to rule out the bag itself.

 

[m_c]

IIRC about 8 ohm.

 

[jimbo84]

Put it all back together and the light has gone off...for now. Will see whether it comes back on, I've visually checked all the cabling I could see to check for any damage, seems to be ok.

 

[premmington]

Clock spring pulled off. Measured the resistance of it... coming to 1 ohm, fluctuates by 0.02 of an ohm when turning, anybody any idea what they should measure? This was the measurement of the two cables combined using the grounding pin to short out the plug end.

Similarly anybody know what the resistance of an airbag should be? So I can replace the bag for a resistor to rule out the bag itself.

2.2ohm to 3.3ohm depending on loop diagnostic voltage. 12volt or 5volt logic?

 

[premmington]

Put it all back together and the light has gone off...for now. Will see whether it comes back on, I've visually checked all the cabling I could see to check for any damage, seems to be ok.

Drown clock spring in switch cleaner.

 

[jimbo84]

2.2ohm to 3.3ohm depending on loop diagnostic voltage. 12volt or 5volt logic?

Not sure on voltage, is that the voltage of the test meter or the voltage of the car control module? If it comes back on I will try the resistor in place of the bag.

Drown clock spring in switch cleaner.

I have some spray isopropanol alcohol from RS will this act as a cleaner?

 

[m_c]

Often a light layer of oxidation builds up on connectors which is enough to trigger a fault. Unplugging them, and plugging them back in usually fixes them for a while.

If the faults cleared, I wouldn't worry about it for now.

If it's a clockwork spring type setup, then contact cleaner won't do any good, however if it's a contact ring setup, then it'll possibly clean the contact tracks.

 

[Wightsparks]

Is there not an issue testing airbags with a multi meter?

 

[jimbo84]

I've learnt today that they have grounding pins that short the terminals together as soon as the plug is removed from an item of the airbag system and that to test you need to move away the grounding bar from the pins as the plugs do when they connect.

I also believe that so long as your multi meter isn't producing 12v to test you're OK but I wasn't risking it.

The airbag control module applies a test voltage through the airbag circuits to test resistance of the circuits so there must be a safe test voltage/current as every time you turned the ignition on and the module tested the circuits they'd all go off.

I'm sure someone like @premmington will be able to confirm how safe it is to test them.

 

[m_c]

The airbag module does put a very small current through airbags/pretensioners for self test purposes, but you should never test a detonator directly with a multimeter.
It's highly unlikely a digital multimeter would trigger one, but it's just not worth the risk.

Any wiring checks should be carried out with detonators disconnected.

 

[premmington]

I've learnt today that they have grounding pins that short the terminals together as soon as the plug is removed from an item of the airbag system and that to test you need to move away the grounding bar from the pins as the plugs do when they connect.

I also believe that so long as your multi meter isn't producing 12v to test you're OK but I wasn't risking it.

The airbag control module applies a test voltage through the airbag circuits to test resistance of the circuits so there must be a safe test voltage/current as every time you turned the ignition on and the module tested the circuits they'd all go off.

I'm sure someone like @premmington will be able to confirm how safe it is to test them.

All mechanics are small boys at heart - how ever old you are - I am 53 - the temptation to take an old air bag out into the yard and deploy it - is just too much.

They can be deployed at 9v - I know this - we have had great pleasure at doing it with a 9v battery several times...

Your multimeter will calculate resistance by volt drop - it will induce a known voltage and measure the actual voltage in circuit - this is how they work.

Testing actual resistance of a airbag detonator with a multimeter is a definate NO NO...

But - specific multimeters for Automotive work - tend to have two AA 1.5v batteries - to give an open circuit voltage of 3volt - my Facom 711 (Chauvin Arnoux 5220) takes 2x AA 1.5volt batteries.

The correct way to measure the resistance of an airbag detonator is to take a scope amplitude reading of the diagnostic protocol pulse to earth from the lead ingoing wire - and from the outgoing earth wire - then use OHMs law to make you calculation.

In the real world - you will have a break out lead with a 2.2ohm or 3.3ohm load (resistor) in it - subsitute it for the air bag pack and re- read the error codes with a scan tool.

For your info: You would not believe how many sub five year old - high value cars - we strip plastic trim away to find resistors soldered into airbag circuits. You gotta ask what would happen - not happen in accident - who is doing this to newish cars - the dealers/factory? (the slavage industry).

 

[zx9]

2.2ohm to 3.3ohm depending on loop diagnostic voltage. 12volt or 5volt logic?

On the B5 Audi / Passats seat airbag monitoring on the drivers seat is disrupted by damaged cables, damaged due to regular movement of the seat. There was an Audi service bulletin (ref. VCDS Wiki ) saying to disconnect the seat wiring and fit a 2.4 ohm resistor to the now empty plug so the car can see the phantom seat air bag. The bulletin had a pdf for the customer to sign acknowledging the work had been done, stating that the car had been homologated both with and without the side air bag.
Obviously you would not do this to a driver or passenger airbag but it holds up @premmington 's observations that the diagnostics are looking for 2.2 to 3.3 ohm.

 

[premmington]

On the B5 Audi / Passats seat airbag monitoring on the drivers seat is disrupted by damaged cables, damaged due to regular movement of the seat. There was an Audi service bulletin (ref. VCDS Wiki ) saying to disconnect the seat wiring and fit a 2.4 ohm resistor to the now empty plug so the car can see the phantom seat air bag. The bulletin had a pdf for the customer to sign acknowledging the work had been done, stating that the car had been homologated both with and without the side air bag.
Obviously you would not do this to a driver or passenger airbag but it holds up @premmington 's observations that the diagnostics are looking for 2.2 to 3.3 ohm.

To clarify - the OHM rating I stated is for airbag detonators - they are fairly universal.

Seat mats are a differing thing - I normally measure the other good seat to get a referance resistance.

Most logic circuits for diagnostic protocols for anything on a car work on the ranges I have stated. It is how chips work - too much load would give too much current - you ECU is looking for switching - not full drive and phase actuation.