I recently had to replace the radiator in my 99 C70. Things ran well before the repair minus the leaking radiator, here's where the problems start.
I like to work on a clean motor compartment so I pressure washed under the hood. I then went to move the car and the "flashing" transmission arrow came on along withe check engine light. Well I did change the radiator and would tackle the trans issue later. Radiator switch went well. Pulled the computer codes and got a p0702, p0758, p0748 and a p1618 with the 708 and 1618 there is a missed communication between computers and transmissions.
I cleaned all the topside connections, are there other transmission wiring connections? Oh and it shifts fine 2,3,and4, but no first gear
Any ideas welcome. I think it all started with the under hood wash
Gene

 

Sounds like your PNP switch is acting up leaving the car in "winter" mode (where the computer starts the transmission in 2nd gear). Try the "shifter row" first ( go from park to lo to park 20x fast). If that doesn't help, search Youtube for PNP switch replacement vids - you may just need to check if the connector got unseated or you may need to replace the switch. Don't drive too long without fixing this or you are risking the transmission.

 

I have done the "racheting" of the shift lever, and the backup lights have always worked. I had my trusted ASE Master mechanic pull codes and he found more codes than I could pull with my Acton reader. His advice its an electrical wiring problem, not a PNP switch. He said check grounds and connectors DUE to the problems starting after washing the engine bay.
There is no limp mode there is no flaring, the engine runs like a dream, the car engages reverse without hesitation. The problem is the transmission is not getting the signal to start in 1st gear, and not allowing the cruise control to even turn on when the minimum speed should allow.
Are there ground connections that are prone to corrosion?

 

Remove dry and reseat your ECM. Check connections. I hose or power wash all my engine compartments. Good luck !