You can drive, but do not put it off
Hard to start when hot
It starts instantly from cold, but after a drive it cranks for a long time and catches reluctantly. Pressing the throttle sometimes helps.
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
- Fuel trims right after a hot start: a deep negative means there was too much mixture.
- Intake air temperature: the unit accounts for hot under-bonnet air, and a lying sensor upsets the calculation precisely when hot.
- Rail pressure after switching off, if the car reports it: falling pressure points to a valve or an injector.
- Evaporative system codes: a purge valve stuck open pushes petrol into the intake while the car stands.
Common causes, cheapest first
- A purge valve stuck open — the most common and the cheapest cause.
- A leaking injector: overnight it floods the cylinder.
- An air or coolant temperature sensor that lies when hot.
- A weakening fuel pump: it copes cold and no longer copes hot.
Codes that show up with this
P0443Evaporative emission purge control valve circuit malfunctionP0455Evaporative emission system leak detected (gross leak)P0171System too lean (bank 1) — air leak or not enough fuelP0111Intake air temperature circuit range/performance
These parameters in the reference
Short term fuel trim B1Long term fuel trim B1Intake air temperatureCoolant temperatureFuel pressureFuel rail pressureFuel rail pressure (rel. to manifold)
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.