My wife's 2006 Trailblazer has about 110k on it. It has been well maintained. At about 50K I replaced the fuel pump because the fuel gauge was no longer working. Now I'm back to the same problem - suspect I replaced with another faulty pump. Normally you turn the key let go and the vehicle cranks till it starts. With the faulty fuel gauge, you have to hold the key forward until the engine starts. Due to her/our programmed brains, we often attempted to start the truck and release the key before it actually started. Check engine light would come on. For some time now, we have been using the trip odometer to keep track of the gas level. I finally decided to have the light checked a few days ago. PO131, POO30, PO135, PO300, PO463, PO304. The codes were cleared and today I'm left with PO135 and PO304. The truck runs and drives fine. I think I get the PO135 might be 02 sensor but I'm a bit perplexed on the PO304. The truck runs well with no noticeable miss. I would appreciate any guidance and yes I have to get the fuel gauge issue fixed soon - It's wearing on my wife.