Find the meaning of a diagnostic trouble code, possible causes and what to discuss with your workshop.
P0174 reports a lean condition on Bank 2. The useful next step is to preserve the diagnostic data and find out why fuel control has reached its limit, rather than choosing a sensor from the code alone.
P0171 means the engine control system has detected a lean condition on Bank 1. An air leak can be responsible, but the code does not identify a failed oxygen sensor or a specific replacement part.
P0420 means the catalyst system on Bank 1 is performing below its accepted efficiency threshold. The result needs diagnosis: it is not, by itself, an instruction to replace an oxygen sensor or catalytic converter.
P0300 reports a random misfire. Ford’s diagnostic reference describes multiple cylinders misfiring or a misfire that the control module cannot assign to one cylinder.