What is the cause of P0171-00 fuel trim system lean?
2 Answers
P0171-00 fuel trim system lean fault causes are as follows: 1. Air leak after the mass air flow (MAF) sensor. 2. PCV system leak. 3. Oxygen sensor failure, exhaust leak near oxygen sensor. 4. EGR leak. 5. Mass air flow (MAF) sensor failure. 6. Fuel filter is too dirty, fuel pump supply insufficient. Solutions for P0171-00 fuel trim system lean fault: 1. Check oxygen sensor, inspect throttle intake manifold for leaks. 2. Fuel trim malfunction may cause default operations such as harsh shifting, ABS/traction control system warning light illumination, etc. Perform fuel system maintenance, drive at high speed for several kilometers, finally replace MAF to solve the problem.
I've encountered quite a few P0171 trouble codes in the auto repair industry. It indicates a fuel system too lean, meaning there's too much air and too little fuel in the engine's air-fuel mixture. Common causes include intake system leaks—such as cracks in vacuum hoses or intake manifold gaskets allowing extra air to enter; faulty oxygen sensors may send incorrect data misleading the ECU's adjustments; fuel issues like insufficient fuel pump pressure, clogged fuel filters, or dirty injectors causing inadequate fuel supply; a dirty MAF sensor can also affect air intake readings leading to errors; sometimes EVAP system leaks or poor fuel quality add to the trouble. For diagnosis, first use an OBD scanner to check fuel trim data streams—if long-term trim exceeds 10%, it confirms the issue; manual checks: listen for hissing sounds to locate leaks, perform a smoke test for vacuum leaks, and check if fuel pressure is within normal range. Driving with a lean condition for too long may cause engine overheating, damage the catalytic converter, or even burn out the engine. Don't delay—get it handled by professionals promptly, safety first.
