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Quick background - I picked up a 2000 S3 track day toy for little money a few weeks back - its pretty much good to go with decent suspension, brake, transmission & engine upgrades. Road legal, harnesses etc. I want to play with that while I have work in progress on the S2 - there will likely be some lessons to learn from that which I can transfer into the S2 - although I don't think an S2 will ever suffer from the mighty torque steer that the S3 exhibits. The car wasn't without a few niggles - almost all electrical issues caused by lack of knowledge from previous owners, including someone else who was a bit hasty with the Stanley knife when trimming carpets.
So I now have the dubious pleasure of owning an S2, S3 and S4 - the "manopause" must be in full flow. I've been through a fair number of tidy up jobs and enjoyed the nuances of the S3. This one has the controversial PowerTrak Haldex mod so it runs 50:50 torque split all the time - handles nicely on smooth tarmac, but way too stiff (imho) for bumpy Irish B-roads on its fully adjustable coil-over suspenders.
Thought I would share how I deactivated the airbags... reason being the MOT men (its a local government facility here, not a friendly garage like mainland UK) are very keen to see airbag lights behave correctly on the dashboard. I had three cars through MOT in the past month and in all cases they made a point of checking this. The S3 only had the passenger side airbag connected when I bought it, but obviously the airbag light comes on and stays on which is probably an MOT failure (even though the car no longer has any airbag components fitted) or one of those really annoying conversations with the womble in charge which generally results in an argument and a retest fee. That and it annoys me being on all the time - I was thinking of opening the cluster and removing the lamp (its actually an LED) but then decided to work it out from first principles.
Firstly, unplugging the airbag controller (sitting at the most forward part of the central tunnel) does nothing regards the warning lamp on the cluster - I figured that from the wiring diagram - the connectivity from airbag controller to the cluster is via some form of logic circuit in the cluster that looks for active control from the airbag to determine if the light is on or off.
With the airbag controller unplugged, it also causes a fault code on the ECU - no biggie of course as it doesn't light up the cluster, but it just complains about lack of OBD comms with the airbag controller.
So I wanted to discover what resistance values on the airbag connectors make the alarms go way - to make the controller happy - to see how it informs the cluster when it is happy.
Having chopped the loom at a strategic location, I was able to hook up an OBD plug with VCDS and a couple of 10ohm cermet resistors. I found that a value roughly in region of 2-4 ohms was good to clear faults for airbag ignitors or seatbelt tensioners. I also recoded the airbag controller to "00002" so that it ignored all components except the front tensioners and airbags. Then I discovered that a single 2.2R resistor can be placed across both pairs of airbag pins and another 2.2R similarly across both front tensioner pins keeps the alarms off.
When the airbag controller is happy, it pulls pin 68 to 0V - that is the logic signal used on the cluster. The lamp only goes off when that pin is switched to 0V.
So now I have three possibilities:
1 - Keep the airbag controller out of the car and simply hardwire what would be pin 68 to 0V ==> airbag light always off, but fault code remains on ECU
2 - Also with the airbag controller removed, build some simple timer circuit that drives pin 68 to 0V approx 4s after the ignition is turned on so it proves the light works !
3 - Fit the airbag controller with minimal wiring (12V, 0V, K-wire & Cluster Signal) and a pair of 2.2R resistors on vehicle side to fake airbags etc ==> light behaves correctly and even the ECU is happy !
So I now have the dubious pleasure of owning an S2, S3 and S4 - the "manopause" must be in full flow. I've been through a fair number of tidy up jobs and enjoyed the nuances of the S3. This one has the controversial PowerTrak Haldex mod so it runs 50:50 torque split all the time - handles nicely on smooth tarmac, but way too stiff (imho) for bumpy Irish B-roads on its fully adjustable coil-over suspenders.
Thought I would share how I deactivated the airbags... reason being the MOT men (its a local government facility here, not a friendly garage like mainland UK) are very keen to see airbag lights behave correctly on the dashboard. I had three cars through MOT in the past month and in all cases they made a point of checking this. The S3 only had the passenger side airbag connected when I bought it, but obviously the airbag light comes on and stays on which is probably an MOT failure (even though the car no longer has any airbag components fitted) or one of those really annoying conversations with the womble in charge which generally results in an argument and a retest fee. That and it annoys me being on all the time - I was thinking of opening the cluster and removing the lamp (its actually an LED) but then decided to work it out from first principles.
Firstly, unplugging the airbag controller (sitting at the most forward part of the central tunnel) does nothing regards the warning lamp on the cluster - I figured that from the wiring diagram - the connectivity from airbag controller to the cluster is via some form of logic circuit in the cluster that looks for active control from the airbag to determine if the light is on or off.
With the airbag controller unplugged, it also causes a fault code on the ECU - no biggie of course as it doesn't light up the cluster, but it just complains about lack of OBD comms with the airbag controller.
So I wanted to discover what resistance values on the airbag connectors make the alarms go way - to make the controller happy - to see how it informs the cluster when it is happy.
Having chopped the loom at a strategic location, I was able to hook up an OBD plug with VCDS and a couple of 10ohm cermet resistors. I found that a value roughly in region of 2-4 ohms was good to clear faults for airbag ignitors or seatbelt tensioners. I also recoded the airbag controller to "00002" so that it ignored all components except the front tensioners and airbags. Then I discovered that a single 2.2R resistor can be placed across both pairs of airbag pins and another 2.2R similarly across both front tensioner pins keeps the alarms off.
When the airbag controller is happy, it pulls pin 68 to 0V - that is the logic signal used on the cluster. The lamp only goes off when that pin is switched to 0V.
So now I have three possibilities:
1 - Keep the airbag controller out of the car and simply hardwire what would be pin 68 to 0V ==> airbag light always off, but fault code remains on ECU
2 - Also with the airbag controller removed, build some simple timer circuit that drives pin 68 to 0V approx 4s after the ignition is turned on so it proves the light works !
3 - Fit the airbag controller with minimal wiring (12V, 0V, K-wire & Cluster Signal) and a pair of 2.2R resistors on vehicle side to fake airbags etc ==> light behaves correctly and even the ECU is happy !
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