ESP Light comes on after 10 minutes driving
 

I hope someone can help me with this.

I have a 2007 Audi A6 estate automatic and the ESP fault light comes on 10 minutes after starting the engine (doesnt matter if I've been driving or not). I have had someone look at it and they give me a fault code P1857 which points to the Mass Airflow Meter being defective.

However, earlier in the year I had a problem with the boot seal which meant that around 3 inches of water had collected in the tyre well. The water had been there for some time before I realised and I'm not sure if this may have affected the electrics in the car. Also from time to time I get a warning on the car that says the battery level is low even know I replaced the battery only a few months ago. There is also an intermittent warning that the break light bulb needs replaced.

In the last week I've also had to get the gearbox reconditioned due to a rod snapping (turned out to be very expensive).

Any thoughts on this would be truly welcomed.

Many thanks
Don