P0421 Warmup Catalyst Efficiency Below Normal (Bank 1)
* Air leaks at the exhaust manifold or in the exhaust pipes
* Catalytic converter is contaminated, damaged or has failed
* Front HO2S and/or the rear HO2S is loose in the mounting hole
* Front HO2S older (aged) than the rear HO2S (HO2S is lazy)
* Front HO2S or rear HO2S is contaminated with fuel or moisture
Vehicle driven at a speed of 17-74 mph at 1500-3000 rpm with the calculated engine load from 15-48% for 2-3 minutes, and the PCM detected the inversion ratio of the rear HO2S was close to the inversion ratio of the front HO2S during the Catalyst Monitor test.
This code sets in 2 Trip(s).
P0171 Adaptive Fuel Trim Too Lean (Bank 1)
* Vehicle driven low on fuel or until it ran out of fuel
* One or more injectors restricted or pressure regulator has failed
* Fuel delivery system supplying too much or too little fuel during cruise or idle periods (e.g., faulty fuel pump, or dirty fuel filter)
* Air leaks after the MAF sensor, or air leaks in the PCV system
* Air leaks at the EGR gasket, or at the EGR valve diaphragm
* Exhaust leaks before or near where the front HO2S is mounted
* HO2S is contaminated, deteriorated or it has failed
* Fuel control sensor is out of calibration (i.e., ECT, IAT or MAP)
* Base engine "mechanical" fault affecting one or more cylinders
Engine running in closed loop at cruise speed for 2 minutes, and the PCM detected the A/F ratio remained leaner than the fuel correction limit in memory for 10 seconds during the Fuel System Monitor test.
This code sets in 2 Trip(s).
Hope this helps.