EGT Sensor Fault

Bill Asked: (The other Bill !)
How does the engine operate differently when Lane A is flashing?

You have the question backward.
You should be asking, "When the Lane A lamp flashes, What in the engine is operating differently.

The Garmin is recording the Effect of the Fault (Cold EGTs) not the Cause of the Fault (???).

When the Lane A lamp illuminated, Lane B took control of the failed system, restoring the engine to normal operation.
When the Lane Light Flashed, it saw a fault and logged the fault to the ECU Error files.
Connect the BUDS Software to the engine and interrogate the ECU Fault File.
Then you will know what the true cause is instead of blindly replacing good parts and guessing at the problem.

I have a similar problem with my RV-12iS.  It has a Rotax 912iS engine with about 75 hours.  I can create an EGT 3 Sensor Fault by flying at night and reducing throttle to Idle.  I then begin a descent, simulating engine out failure. 

Watching the EGT gauges, I can see EGT 3 cool down slower than the others, and it remains quite a bit hotter, by maybe 200-300 deg.  Lane A comes on Flashing; look at Engine Faults, see: LANE A SENSOR EGT 3.

I believe the problem is a result of the LOCATION of EGT 3 sensor on my engine.  It is buried toward the rear of the engine and is close to the oil canister and surrounded by hoses.

The result is EGT 3 is reading correctly, but a higher temperature because the exhaust is higher.  Cycling Lane A status turns off the flashing LED, engine runs fine.

This does not happen under identical circumstances during the day when OAT is higher.

The EGT Sensor is measuring the Temp of the Exhaust Gases 5cm from the Exhaust valve in the middle of the gas flow.
It is NOT measuring the temperature of the metal of the Exhaust pipe.
If the Fault says  " LANE A SENSOR EGT 3",  I would tend to believe it is a Sensor Fault.
Swap the Sensor with that of another cylinder and see if the fault moves.

Problem fixed :)

Finally received a dongle so I could read the BUDS error logs (the dongle was on back-order for 4+ months). It showed multiple injector errors on lane A cylinders 1 & 4. So I replaced fuel injectors 1 & 4 and the problem has gone away. I notice that the engine now also starts better and runs smoother when I do a lane check with lane B turned off. FYI it wasn't that hard to replace the injectors... took about 1-1/2 hours start to finish.

I'm surprised that I had to replace 2 injectors after only 280 hours on the engine. I run only premium mogas. I also see that other people seem to have the same problem needing injector replacements. Has anyone successfully used fuel injector cleaners in their fuel system?