You can drive, but do not put it off
Will not start in Park
In P the starter is silent, but in N the car starts. Or the other way round. Sometimes every gear letter lights up at once; sometimes cruise control will not engage.
You can usually get home or to a garage, but every day of delay adds to the bill.
What to look at in the live data
- Which gear the unit sees: if it does not understand the selector position, it will not allow the starter.
- Whether there is a brake light switch code — it governs both coming out of Park and the cruise control.
- Selector position sensor codes: often it is not broken but merely out of adjustment.
Common causes, cheapest first
- A selector position sensor knocked out of adjustment after a repair. Adjustment is free; the sensor is not.
- The brake light switch: a penny part on the pedal, replaced without removing anything.
- The sensor connector or wire — underneath, in the dirt.
- A worn selector linkage: the lever is in P but the mechanism did not get there.
- The position sensor itself — checked last.
Codes that show up with this
P0705Transmission range sensor circuit malfunctionP0850Park/neutral switch circuit malfunctionP0571Brake switch circuit malfunction
These parameters in the reference
Lamps that may be on
Do it step by step
P0171 is not a random string but an address. We take it apart, sign by sign.Reading a fault code: the letter and four digits
A symptom is not a diagnosis. The same sign comes from a dozen different causes — the readings are what tell them apart, not the feeling.
How the app helps
CarScan shows exactly these readings live, remembers the highest and the lowest value of the trip, and puts them into a report you can hand to a mechanic.