Hey guys I was wondering my Blazer ia showing these 3 codes, Service engine light came on. I was wondering, would these DTC'S being in the computer would it keep the monitor's for Catalyst and Secondary air from running? All other monitors are ready. I let it sit for 4 hours and when i started it again SERVICE ENGINE SOON light is now off. when the light came on last I only read the codes, not deleted them. Thanks guys i hope some one has a answer !! I have also now replaced my MAF as it was showing the code for Maf range /performance.

 

the number one fix for the 171 and 174 is the MAF. make sure the air boot around the maf isnt torn or loose. usually those codes mean theres a air leak somewhere after the MAF like the rubber boot, throttle body gasket, intake gasket, pcv, etc