Check engine code PO420 and PO171

[Canaris]

Trying to find the issue with 2006 1.3L Yaris hatch:

Check engine light comes on after driving for a while, usually after highway use.

Other than the check engine light coming on the car is running very well, good fuel consumption, smooth idle and acceleration.

Get a PO420 but if I do not clear it, will through a P0171 code as well.

Mechanic said PO420 is the most difficult code to troubleshoot due to being generic. 

Connected to his expensive professional diagnostic equipment, could not find the issue.

Encouraged me to keep trying things, suggested to clean the throttle body, which I have done. 

Car now runs better with faster acceleration. 

My scan tool does not produce live data but will post Freeze Frame of when the issue happens, 2x examples

DTCFRZF   PO420   PO420

FUELSYS1   CL   CL

FUELSYS2   N/A   N/A

LOAD_PCI(%)   56.5   63.1

ETC(C)   83   83

SHRTFT1(%)   -1.6   -6.3

LONGFT1(%)   -3.9   -3.1

RPM(/min)   2131   1914

VSS (km/h)   42   51

SPARKADV( )   31   28

IAT(C)   41   43

MAF(g/s)   7.79   10.17

TP(%)   20.0   22.0

O2B1S1(V)   0.740   0.625

SHRTFTB1S1(%)   -1.6   -6.3

O2B1S2(V)   0.740   0.700

RUNTM(sec)   693   606

EVAP_PCI(%)   23.5   51.4

WARM_UPS   5   6

CLR_DIST(km)   122   59

BARO(kPa)   103   103

CATEMP11(C)   560.70   589.50

CATEMP12(C)   560.70   589.50

VPWR(V)   13.632   13.632

LOAD_ABS(%)   32.0   46.7

EQ_RAT   1.000   1.000

TP_R(%)   4.3   6.3

TP_B(%)   52.5   55.3

APP_D(%)   20.4   22.4

APP_E(%)   35.7   37.6

TAC_PCT(%)   19.6   21.6

CLR_TIME   3:h:06m   1h:49m

 

Will purchase a better scan tool that does provide live data if required. Hoping someone can see an irregularity or a maxed-out threshold in this data and tell me what to look for?

Do not think it is smart to keep replacing parts without knowing it is likely to fix the problem.

Thanks in advance for any comments or suggestions.

Edited November 29, 2020 by Canaris

[campbeam]

Have a thorough read of the attached links. I would be inclined to start by cleaning the Mass Air Flow sensor. Next step would be to remove and clean the O2 sensors

https://www.fixdapp.com/blog/p0420-toyota

https://www.fixdapp.com/blog/p0171-toyota

When all else fails, suggest that you go to a Toyota dealership and get them to use their diagnostic equipment to identify the underlying cause.