I've had problem with my airbag system at 3 connectors, the driver and passenger pretensioner connectors (the yellow and orange ones aft of the airbag ECU) and passenger airbag switch connector. The airbag check light will come back on weeks or months after I have reset it.
I think it all comes down to insufficient contact at the connector. A connector is typically made by crimping the metal contact to the wire, then the metal contact is inserted into a slot in the plastic connector body. There is a tongue in the metal contact which hooks into an opening the slot so that it stays put. What this means is that when you insert the metal contact into the connector body, you will hear a 'click' as the contact snaps into place and cannot be pulled out.
My guess is that after repeatedly connecting and disconnecting the connector, the plastic opening in the connector body is now slightly larger. As a result the metal contact can move quite a bit within the connector. So as you mate the connectors again, the metal contacts does not engage as much as it should.
For the passenger airbag switch connector, after I have made the connection, I pushed the metal contact slightly through the opening to make it engage more. I have not had problem with it since.
For the pretensioner connectors, I cannot see how the metal contacts engage to the body, so I just used a jeweler screwdriver to push on the metal contacts from where the wires emerge. The other thing is that there are plastic brackets on the floor for the pretensioner connectors to snap into to keep things neat and tidy. Unfortunately when the connectors are in, there is a little bit of tension on the cables. Once in a while vibration from uneven road or hitting potholes will set off the airbag light again. So now I do not clip the connectors into the bracket. I have not had airbag light on since.
So dannyboy, it looks like your case is similar except it is happening at the ECU connector. Hopefully this is the end of it. What a saga.
Last edited by gwinter; 18-12-15 at 06:20.