The reason you can’t start the engine in second gear is for safety reasons. Car makers fit what’s called a Neutral or Park switch, which means the engine won’t crank unless the car is in Neutral or Park. That prevents the car starting in gear and taking off.

If the lever’s connection to the transmission has failed or become excessively worn, you can get the symptoms you have because the lever won’t select Neutral or Park. And therefore the engine won’t start.

However, it’s highly questionable that this is connected to the limp-home mode. That’s usually caused by a problem with the driveline that threatens to do more damage if you continue driving. The gear lever problem sounds more like a simple mechanical issue. Did both things happen at the same time? If not, they’re very probably not related.

Those codes are reasonably common ones. The first two (0193 and 0089) generally relate to a problem with the fuel rail, specifically the pressure in that rail. This is obviously critical to how the engine runs.

The third code (0401) is more commonly associated with the flow of the EGR valve. If this valve is damaged or blocked, then this fault code would likely show up. As such, you may find you have two separate problems, rather than a single one.

Low pressure in the fuel rail would certainly explain why the performance is off, and the overheating could easily be associated with an EGR valve failure. A blocked EGR can raise combustion chamber temperatures while a failed EGR can actually leak coolant and allow the engine to overheat that way.

Seeking the help of a diesel engine mechanic is a good idea, they often have greater expertise on diesel engines than mainstream dealers and can make repairs at a lower cost to you.