What does code P0171 mean?
P0171 means the mixture on Bank 1 is lean: too much air and too little fuel. The engine computer has added fuel to correct it but has reached its limit. A 4-cylinder engine only has Bank 1.
Why does code P0171 appear?
- An air leak into the intake: a cracked vacuum hose or intake gasket.
- A dirty or faulty mass air flow (MAF) sensor.
- Low fuel pressure: a weak fuel pump or clogged fuel filter.
- Dirty injectors.
- An exhaust leak before the O2 sensor.
What can you safely check for P0171?
- With the engine off and cool, look under the bonnet for a rubber hose that has slipped off or cracked. Don't touch a hot engine or a running fan.
- Check the air filter: if it is very dirty or full of dust, replace it. Make sure the filter box is closed properly and its clamps are tight.
- Check whether P0174 is also present. If both are, the cause is often shared by both sides, such as an air leak, the MAF sensor or fuel pressure.
Is it safe to drive with P0171?
If the car drives normally, you can drive gently and get it checked within a few days. Running lean for long can make the engine run hot and start misfiring. If it jerks or the light flashes, go to a mechanic straight away.
Safety: never remove the radiator cap on a hot engine; boiling coolant can burn you. Keep your hands away from the fan and belts while the engine runs. If you smell fuel, switch off, keep any flame or cigarette away and call a mechanic.
When should you call a mechanic?
If the hoses and air filter are fine and the code comes back, have a car mechanic (mistri) check it. They can find air leaks with a smoke test and measure fuel pressure with a gauge.