Airbag SAC_TEMIC B660 fault code

Hi all

I took on a project car requiring a new engine and hit an MOT issue which consists of

Passenger's airbag deactivation switch short circuit to earth (B660) using Autel Maxicom MK808BT

I was told to check under seat wiring which all looks ok, I checked the passenger airbag key disable terminal also and everything looks good. Could it be that the actual switch is at fault here?

I have tried disconnecting the key deactivation and it shows open circuit then re-connected and it show short circuit. Ordered a new key de-activation unit off ebay but as I'm now on a 7 day MOT failure clock, I wondered if there was any advice?

The cable disappears behind the dash and unsure where it goes to. Are there any ohm readings across the key switch I could check for starters? I have a haynes but they only made the older model book not one for a 12 plate.

First Citroen here and I'd like this right by weekend to get it passed through.

Cheers

The trouble with this is that you don't know the history of the car.

You can get 'odd' faults like 'not defined' and the like when people swap out ECUs (AIRBAG ECU in this instance) and its not configured to the car properly (or configure the car to the AIRBAG)

So you may not have the fault that the description leads you to.

C3CAR wrote: ↑Wed Nov 13, 2019 11:37 am The trouble with this is that you don't know the history of the car.

You can get 'odd' faults like 'not defined' and the like when people swap out ECUs (AIRBAG ECU in this instance) and its not configured to the car properly (or configure the car to the AIRBAG)

So you may not have the fault that the description leads you to.

Well the car belonged to a friend and he has never seen the code on the dash and neither myself or friend that worked on the car remember seeing it during rebuild either. The first time it struck me being there was after a full valet hence why I headed for the seat area first ie water ingress.

Hopefully the new switch arrives soon and either fixes the issue or takes it out of the equation and then I'm guessing its a case of going through the system and verifying continuity and checking voltage and/or earth paths per section.

Any idea what voltage should be expected throughout?

The switch would create a "high" and "low" logic to indicate enabled and disabled. The "low" logic cant be ground (o volts) as this would indicate a failure, so normally the logic would be above ground . You would have to assume an open circuit would be a fail too. This typically is indicated as "open circuit or short to positive".
You can try removing the plug from the switch and see if the warning changes. If it changes to open circuit, the fault is in the switch. If it doesn't change then its crushed or ECU.

OK well I solved the issue. I spoke to an auto-electrician after swapping the switch with no change. I mentioned the switch went open circuit when removed and he said this indicated the wiring was likely ok and to check the airbag ecu.

I removed the centre console to get to the ecu between the gearstick and handbrake (mk2) and removed the battery negative. When I removed the cable harnesses from the ecu, I saw green corrosion across 5 pins so unbolted the ecu and used isopropyl alcohol to clean off the areas followed by a touch of WD40. Re-assembled, cleared all codes and the fault cleared.

Awesome!

One more thing, using the Snap-on Solus Ultra instead of the Autel Maximus, the code was B3660 rather than the Autels B660

Anyhow, just in case anyone ever gets the same issue, maybe it will help