P0171 to P0420 check engine

About a week after I bought my tacoma the check engine light came on with a P0171 system lean in bank 1 code and I also noticed very poor mpg. The maf sensor was pretty dirty so I cleaned it with maf spray cleaner and reset the check light, mpg was instantly a lot better. Now a few days later check engine light came back on but with a P0420 catalyst system efficiency below threshold- bank 1 code. Also I believe mpg is low again. What should I do next? Thank you

 

Try a new gas cap.

 

Ok , I'll do that tomorrow morning. But shouldnt it be a different code if the gas cap was bad?

 

Ok , I'll do that tomorrow morning. But shouldnt it be a different code if the gas cap was bad?

 

Emissions leak would pretty much start at the gas cap I would think but I could be wrong.

 

P0420 is for air leak in exhaust before rear h02s , AF sensor error, fuel system fault , or faulty catalytic convertor. Not emissions leak I believe

 

Subbed for answer.

 

Gas cap would trigger an EVAP related code. A EVAP leak could cause excess o2 to enter during purge cycles...but causing a lean code by itself, unlikely...possible but unlikely. I would not think that is causing the CEL.

Get yer vacuum gauge out. Check to find a leak, im thinking post combustion as there is a lean code. Might be an EGR line or exhaust manifold that is leaking, that would cause both codes. A manifold leak would turn up on the vacuum gauge. Also you can use an unlit propane torch or carb cleaner over certain points to check for vacuum leaks.

If you have a good scanner (something better then the Torque app, which has a pretty slow refresh rate), you can reset the ECU and then monitor the fuel trim, short and long term. See if it leans out significantly right off.

 

Subbed. I have the exact same problem. I am lucky to get 14 mpg with these codes.

 

Me too i have a 430 and 420 codes any guesses

 

I have just P0171....change MAF? or does the voltage check and ohmmeter check on all data tell you enough good/bad?

 

I used to get the p0420 randomly every few months, after a few O2 sensors my catalytic converter started to rattle, since I've replaced it I've been over a year with no codes. Good MAF clean and check your sensors

 

Rear o2 seemed to get rid of it, has been 300 miles and no light