trouble code help

[dwmmatt23]

check engine light came on and trew 3 trouble codes, p0102 p0402 and a pending p0402. anybody shed some light on this for me?

 

[dwmmatt23]

i picked up a handheld code scanner pretty cheap and cleared those codes. the next day they came back on. then my brute force intake arrived so i put it on and cleaned the mass air flow sensor and cleared the codes, they didnt come on all day yesterday. then today i get 2 more codes, a p0420 and
p0420 pending. its says its catalyst below expected values bank 1 i think, anybody know whats going on? the previous 3 codes were for MAF low current and egr flow i think.

 

[badtothe bone]

DTC PO102 = Mass Airflow Sensor - circuit low frequency.
Usually caused by a broken Mass Air Flow Sensor - or a loss or broken connection.

DTC PO402 = exhaust gas recirculation flow excessive
http://www.obd-codes.com/trouble_codes/chevrolet/

 

[dwmmatt23]

Actually the exhaust has been on forever with no codes, and the codes started before I did intake, this new one just came one. Same setup alot of people run with no problems

 

[badtothe bone]

If you read the link, you can diagnose the problem and then see if you need to buy a new unit or just repair the terminals on the one you already have.

Maybe you could get a junkyard to sell you one cheap and you could try theirs to see if the MAF is bad or not.

 

[dwmmatt23]

well i havent had those two codes come up in over a week after i cleaned MAF and installed my intake. however ive been getting a p0420, low catalyst threshold bank 1, if i clear it it comes on the next day. should i just try replacing the o2 sensors after the cats? or is there something else to try or am i just going in the wrong direction? any help would be awesome

 

[dwmmatt23]

anybody know @ how much its gonna cost me to replace my cats? i think there causing a bad rattling ive been having and hopefully the cause of my low mpg