2002 envoy 4.2 p0172

Question

IS THE P0172 REFERRING TO THE DOWNSTREAM 02 SENSOR AND THE
P0171 THE UPSTREAM SENSOR 02
GETTING RANDOM CODE SETS

Answer 1

P0172 Fuel trim too rich Bank 1

Fuel trim are detected by the 02 sensor , the upstream these are known as Sensor 1, The down stream 02 sensor are known as Sensor 2, these are nothing more that catalytic monitor. it just monitor the catalytic convertor. Sensor being the the upstream are the engine management sensor.If your getting a random code, rich and lean if your engine type has a MAF (mass airflow) a faulty MAF can send random rich and lean, you may want to do a MAF cleaning, There is also a fuel pressure regulator , if that fuel pressure regulator vacuum hose is disconnected you will get a random lean code then a rich code,