- Vacuum leaks: A vacuum leak can cause the engine to run lean because it allows unmeasured air to enter the engine. This can be caused by a cracked or damaged vacuum hose, a loose or missing vacuum cap, or a faulty PCV valve.
- Fuel injector problems: A faulty fuel injector can cause the engine to run lean by not delivering enough fuel to the engine. This can be caused by a clogged or dirty injector, a faulty injector solenoid, or a damaged injector wire.
- Mass air flow (MAF) sensor problems: The MAF sensor measures the amount of air entering the engine. If the MAF sensor is faulty, it can cause the engine to run lean by providing an incorrect reading to the engine computer.
- Oxygen (O2) sensor problems: The O2 sensor measures the amount of oxygen in the exhaust gas. If the O2 sensor is faulty, it can cause the engine to run lean by providing an incorrect reading to the engine computer.
- Faulty fuel pressure regulator: If the fuel pressure regulator is faulty, it can cause the fuel pressure to drop, which can lead to a lean condition.
If you are experiencing error codes P0171 and P0174 on your 2000 Nissan Maxima, it is important to have the vehicle diagnosed by a qualified mechanic to determine the exact cause of the problem.
