Do not drive
It smells of petrol
A fuel smell in the cabin or around the parked car. Sometimes with the Check Engine lamp on.
With this symptom you should not keep driving: the trip will cost more than a tow truck.
What to look at in the live data
- Evaporative system codes: P0455 and its relatives. They speak directly of a leak.
- Fuel trims: a strong negative value can mean a leaking injector.
- But here the readings matter less than your eyes and nose: look under the car and in the engine bay.
Common causes, cheapest first
- A fuel cap that is not properly closed — ten seconds to check.
- A cracked hose in the evaporative system.
- A leaking fuel line or injector.
- A corroded tank.
Codes that show up with this
P0455Evaporative emission system leak detected (gross leak)P0442Evaporative emission system leak detected (small leak)P0457Evaporative leak — fuel cap left looseP0456Evaporative emission system leak detected (very small leak)P0440Evaporative emission system — malfunction
These parameters in the reference
Short term fuel trim B1Long term fuel trim B1Short term fuel trim B2Long term fuel trim B2Fuel pressureFuel rail pressureCommanded equivalence ratioO2 sensor B1S2 voltage
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.