I have a 2002 Toyota Camry. I am getting an Chefck Engine Light error code of P0171. I have no idea what is causing this issue. I have replaced the spark plugs, mass airflow sensor, and
Check that the connection for boot between the air filter and the throttle body is good. Or remove the intake boot from the throttle body and clean the throttle plate and bore and/or remove the throttle body unit and clean it (with throttle body cleaner)and put a new gasket on it if its leaking there (may be where the extra air is getting in). look for vacuum leaks or bad (dirty needs cleaning with throttle body cleaner) PCV valve. After that is done remove the negative battery cable for about 5 minutes to reset the memory and start the vehicle in drive it. If light comes back on then you could have restricted fuel injectors (use fuel injection cleaner first then remove and have cleaned or replaced if needed)or possibly a fuel filter that is restricted and need replacing. Intake air leaks (needs intake gasket). Faulty front heated oxygen sensor (check wires or replace). Ignition misfiring (needs tune up or coils). Incorrect fuel pressure( may need filter or pump or regulator). Exhaust gas leaks(before 02 sensor).
Do as enginecreator suggest, make sure and use the appropriate MAF cleaner for cleaning the MAF... P0171 TOYOTA - Air/Fuel Mixture System Lean Bank 1...Possible causes; Intake air leaks, Faulty front heated oxygen sensor, Ignition misfiring, Faulty fuel injectors, Exhaust gas leaks, Incorrect fuel pressure, Lack of fuel, Faulty Mass Air Flow (MAF) sensor, Incorrect Positive Crankcase Ventilation (PCV) hose connection...If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.
What Engine? With due consideration to the above suggestions...may I suggest doing the cheapest and easiest replacement first. Replace the pre-CAT O2 sensor.
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