V70 - Can I Disable Airbag Sensors?

[Jim_V70_2001]

Thanks for your input everyone.

What on earth did we do with old Mark 1 Cortinas, Vivas, Volvo 122's, Spitfires, Vitesses... ??

Our friendly mechanic thinks it is most likely a broken wire under the seat, he says he's seen several before when there are 2 drivers (me and missus) moving the seat back & forth frequently.

So I will hoik out the seat when I get a few free hours and check it out.

Unless someone can tell me where the wire might be broken and if I can get to it without removing the seat? Driver's side.

[reggit]

I'm assuming you've had the codes read to determine that the seat back is at fault?

What error was it? 'resistance too high' would indicate that it isn't connected or has deployed, anything else could indicate an airbag fault.

You'll need to have the code cleared with vida though even if you fix the problem iirc.

[Jim_V70_2001]

Saga continues...

Codes were read, confirmed driver-side airbag fault. The mech took out the seat and indeed found a broken wire as he had expected, and fixed it.

But the message won't clear.

Is this message difficult to clear?

Any help to clear it without a 'puter?

Or maybe possible the wire broke again while the seat was being put back in, I will have to check that.

Thanks.

[Missing Lincs]

The fault setting isn't difficult to clear, assuming the fault is fixed. You need either Volvo's own software and interface or a code reader designed for the job, BSR units will work as with the Autel 702. A code reader won't reset this type of fault unless it has the specific function - even ones that can reset the MIL.

[AndyJudge]

Whats the bigger pain for me is that the cables are easily disconnected by mistake (I knocked mine when shampooing the carpet) but the codes won't go away without a visit to the dealer.

Yes I know they're a safety item etc.. but if they are make the plugs harder to knock apart.

My MOT is in August so I'm hoping some kindly soul can reset the codes for me before then - C70 T5 2001.

[Jim_V70_2001]

The scenario develops...

The codes refuse to clear, another mech friend tried to no avail, and can't get the value from the driver's side air bag. Code translates to "front right side air bag resistance too high - intermittent".

Dealer quoted £400-£700 (plus VAT I imagine) to fix.

Nobody here told me there is a test resistor available to bypass the air bags one by one to find if the air bag or the wiring is the problem. How come? I thought this forum is here to help?

Does anyone know the value of the resistor and the Volvo part number please?

[Jim_V70_2001]

I got them both. This info took a long time to find.

Here they are for others:

1. Volvo SRS Test Resistor (Tool): Part Number: 9988695
You should be able to buy one from your local Volvo dealer. It fits all airbags of many models of Volvo cars and trucks, and is used to temporarily disconnect the airbag to trace the cause of the problem. It also fits the seat belt tensioners for testing those too.

2. Airbag Resistance Value (from the above tool): 1.8 Ohms to 2.5 Ohms

3. Bypass resistor: "Standard" resistor values are 2.2 Ohms (0.25 Watts carbon or 0.4 Watts wirewound). So these should do fine.

I've not tried it myself yet but the tool (and your resistor) plugs into the airbag igniter CABLE connnector once you unplug it from the airbag. It has only 2 pins. The airbag connector should have a shorting device in it which shorts the pins in its connector when you unplug the igniter cable, to try to save you from yourself.

4. There is also an SRS Service Manual here: http://www.dmbruss.com/images/Schema..._SRSairbag.pdf

It is for a Volvo truck but it is the best I could find and seems to be a similar SRS system with useful info in it and there is some troubleshooting info there albeit using different Volvo software (VCADS).

Note:
There are many warnings here and on other forums about the airbag you are working on inflating, but nobody has explained why. Here it is...

How airbags are triggered
The airbag inflator is a chemical cartridge which creates a large amount of inert (harmless) gas rapidly, filling the airbag in a small fraction of a second, and it is "ignited" by "AC signals", not by a DC voltage.

These AC signals are pulses, sent to the airbag inflator by the SRS ECU module when it detects a collision. There are electronic filters in the igniter connectors which try to block any DC voltage and also any pulses which you or a (really dumb, as he's already been told not to do this?) service technician may accidentally cause by shorting the airbag igniter connector pins (this doesn't sound logical) or by trying to measure with a device providing voltage (much more likely).

These filters may sometimes not understand that these AC signals are caused accidentally, and let them through to the igniter. OK, that's human talk, what happens electronically is that the filter, which is capacitive, is "tuned" to only let through the pulses when they occur at frequencies that the igniter expects - but on rare, chance occasions, someone's shaking fingers have created some pulses at this frequency.

Emergency Power Supply
To ensure the airbag will still inflate even if the car's battery is torn out in a collision, the SRS ECU module has a large capacitor which provides enough voltage to keep it working for a few seconds after battery power is lost. By the time you get back into the car after removing and insulating the battery negative terminal, the voltage from the capacitor should have died away. But just to be sure, wait a couple of minutes after you disconnect the battery before working on the airbag or SRS ECU.

Now that you know why, don't try to measure the resistance of any airbag! You don't need to do that. Its resistance is 1.8 to 2.5 Ohms. Use the Volvo SRS Test resistor to bypass a suspect airbag and try to reset the SRS Airbag Service message.

Warning!
Whereas you think you might be safe and know what you are doing, there have apparently been recorded instances in Volvo workshops where trained Volvo technicians have accidentally provided these pulses by using measuring equipment such as multimeters and DVMs, and the airbag has fired, causing injury, sometimes serious injury, to the technician as well as expensive damage to the customer's car.

If it can happen to a trained Volvo techie, it can happen to you and to me too.

So, let's NOT try to measure any airbag's resistance, we don't need to and you just might kill yourself or take one of your eyes out.

So - What's the Safe Way?
1. Turn your ignition to OFF.

2. Disconnect the battery Negative terminal and ensure it cannot touch any part of the car and that the cable cannot get back in contact with the battery terminal. Best to put it into a small thick bag, or posting envelope, or tape it up with insulating tape. Think "safe".

3. Then, just unplug the airbag igniter cable, plug in your Volvo SRS Test Resistor tool into the cable connector (not into the airbag's connector!), and try to reset the SRS code (for the V70 P2 we need the Volvo scan/reset tool or similar scan/reset tool). If the code resets now, then the problem is with the airbag, which has now been disconnected and bypassed. If not, then the problem is in the wiring or the SRS ECU module.

4. If you can't reset the SRS Airbag Service message after you disconnect and bypass the airbag, the most likely cause is a bad connection or damaged wire. In some models the wires under the seat break or catch and tear. The connector pins may tarnish with age and cause intermittent disconnections or high resistance, and this will trigger the code.

5. There may also be wiring connectors under the centre console, or under the carpet in the footwells on some Volvo models. Some people have had bad contacts in these connectors, or they were wet or corroded, which caused the SRS Airbag Service messages. So follow the cables and check to see if there are other connectors out of sight.

6. When you are ready to reconnect your battery, first turn the ignition to ON (position 2). I have not found out why but this instruction appears in several forums. Some people say that the SRS message can be reset in some models by doing this, but I am pretty sure it does not reset it on my V7 P2.

Warning!
Before disconnecting any of the airbag connectors, switch the ignition OFF and then disconnect the battery Negative terminal.

Warning!
Before reconnecting the battery, open one of the car doors and turn the ignition to ON. When you reconnect the battery it is possible that the car may lock, and if your keys are in the ignition... what you gonna do, call the fire brigade?

[Bill_56]

Fascinating write up, grear stuff!

Having experienced the benefit of airbags in a high speed collision a few years ago, I tend to regard them as soft and cuddly.

I swear I remember hearing a loud 'crack' as I felt my body straining against the seatbelt and thinking 'Ah good, that'll be the airbags going off', before nestling down face first into the nice big comfy cushion. I know that thought process sounds infeasible in the few milliseconds it takes, but they do say the world goes into slow motion at such moments!

Anyways, they may be soft and cuddly when needed, but take care, I'm sure they can do damage too... to mechanic and vehicle alike.

The only airbag-related injury I sustained was a slight cut on my forehead when my glasses, which had just been propelled from my face, were pressed back into my face by the airbag. I wonder how common that injury is, and whether it ever results on serious eye damage?

[Jim_V70_2001]

The damage probably results from whatever item or tool the person is carrying, not from the airbag itself I guess.

So your experience with your own specs is also a worry. We should try to remember to "whip 'em off!" just before we collide! lol

[mikealder]

When I fitted seats from an 850R to my V70 I had to disable the electrically fired airbags so I simply soldered a 2,2 Ohm resistor from Maplins across the two wires that go to the seats airbag connector (the green and purple two pin connector) after that I reset the SRS using Vida/ Dice and everything has been happy since.
I still have SIPS bags as the 850R seats were mechanically fired so I simply needed to fool the car into thinking it still had electronic fired airbags fitted which the resistor trick does very well.

As for measuring airbag resistance, it can be done with a specialist meter known as a safety ohm meter, most auto electricians won't have this sort of kit but if you know anyone who works with military aircraft that drop ordinance they will know what one is - Mike