Are you sure you're looking at rust or just factory undercoating and dirt?

Get a small brush (with plastic bristles or even a tooth brush) and start cleaning up the area and reevaluate.

The EX control light will light if the EXhaust exceeds a specific temperature. It is controlled by a sensor in the exhaust and a simple relay-like electronic module.

The OXS light (OXygen-Sensor) is used to remind the driver to inspect the lambda-sensor should be inspected (30 kmiles). Its controlled by a counter connected to the back of the speedo.

So, two completely different systems and functions.

Otto

KNS, I pressure washed everything. The driver side is solid. The passenger side is my concern but not because of the rust. I'm concerned about the hole which allows me to see through the rocker.

In my pic, the red circle is where the surface rust is. Doesn't look or feel like a big rust problem. The green area is where I can shine a flashlight through and see all the way to the front. The driver side is blocked - and according to Otto that's how it should be.
http://forums.pelicanparts.com/uploa...1475254393.jpg

Please realize that the relatively small amount of rust is just a fraction of the rust and damage which is behind the panel. It's like ice in water: 70% is hidden! For a proper repair you need to remove a part of the rear fender, the outer rocker (partly) and the panel where the lock is mounted. Do not just close the holes you are looking at. The inner basic structure of the car can be seriously damaged!

That you seem to have a solid lower B-pillar on the driver side, is no prove that the inner structure is solid. I never saw a 911/912 with this typical rust damage only on one side. Usualy the drivers side was the worst.

Remove the plastic rocker covers - they are glued - and poke with a screwdriver from the top near the holes you marked in the picture. Usually this joint between the verical lock panel and the outer rocker is thin as paper.

Otto