P0299 - Audi A6 2.0 Ultra limp mode

[karlkane]

I've had two similar issues, each traced to a dodgy MAF and MAP sensor. Hiw did I find it? Mapped the car and watched the values on a graph. Each time they started ok, then dropped out but no fault codes generated. Managment system didn't see it as a fault at all so no codes generated.

[Amigo]

I doubt it's the sensors. The car has operated strictly on Shell V-Power Diesel from new, and OMV Diesel MAXX in Europe, never needed a drop of extra oil, oil change at 9,500 miles. I doubt there is another A6 C7 in the UK that has been looked after better. I have looked into this on a number of websites and forums, as well as speaking with various engineers and technicians and the conclusion I drew was that there is a design flaw in the design of the cooling of the Turbo and its software management that leads to this very specific issue under very hot conditions in UK vehicles. I suspect that the calibrations for the UK are different to the ones for Europe, where they seem to be set for different temperature ranges, although I could not get in touch with anyone in Audi to confirm that. Also, driving the car back to Europe at high speeds for a couple of hours in high temperatures to reproduce the conditions to allow me to monitor the values is not feasible...

[karlkane]

25710 is a manifold absolute pressure sensor. This sensor caused me headaches as well, car would work normally then it would fail generating code. Again, when initially graphed I got good and stable readings. After an hour driving it would suddenly drop and fault code would be generated. It was a 17 quid part and mechanics were blaming turbo, dpf, egr etc etc.

[Amigo]

It might be the MAP sensor, but the difficulty is in reproducing the behaviour in the UK, it never gave me any issues here, not even in the hot summer of last year, even though I drove it for more than an hour on motorway in high heat. God only knows, but without a reproducible circumstance I can't really assess it.