2000 Hyundai Sonata P0171 Too Lean - Diagnosis and Fix Guide
I've been struggling with the P0171 'Too Lean' diagnostic code for the past month. I'm due to complete my emissions test in just a few days, but despite cleaning the MAF sensor, checking for vacuum leaks, replacing the O2 sensor, spark plugs, and ignition coils, and cleaning the fuel injectors, the code continues to return. Previously, a misfire code was present, but I believe it has been resolved. I'm at a loss as to what else might be causing this issue. Any advice or troubleshooting steps would be greatly appreciated!
Ideally, using an OBD2 scanner is recommended—monitor fuel trims, MAP sensor readings, and MAF values. Force the O2 sensor to read rich to verify its functionality and check actual O2 voltage outputs. Without a scanner, diagnosing this issue becomes significantly more challenging. I'd suggest performing a fuel pressure test next. Also, did you try the traditional 'spray bottle' method for vacuum leak detection? Please confirm whether the misfire code is still present.