Bob, From what I know the code 26 is where the transmission upshift from 2nd to 3rd is delayed in cold weather because the catalytic convertor is not hot enough yet. My car has the same code and I have not fixed it yet. A search on this code is easy. I don't think it affects the car when it is warm out or the car is warmed up prior to driving.

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dtf
1994 E320 Wagon (Died @ 308,669 miles)
1995 E300 Diesel (228,000)
1999 E300 Turbodiesel ( died @ 255,000)
2006 Toyota Tundra SR5 AC 4X4 (115,000 miles) rusted frame - sold to chop shop
2011 Audi A4 Avant (165,000 miles) Seized engine - donated to Salvation Army
BMW 330 xi 6 speed manual (175,034 miles)
2014 E350 4Matic Wagon 128,000 miles
2018 Dodge Ram 21,000 miles