My 04 SR5 has check engine VHC, and track light on. The truck now has 130,000 miles. She starts up fine runs smooth and has codes PO136, PO156. Replaced all oxygen sensors with OEM Denso, cleaned MAF sensor then replaced it with new OEM Denso one when my mechanic said it was that. He wanted to charge me 350.00 but I new I could pick one up at rock auto for 85.00 so I told him to leave the keys in the mail box at his place and I would pick them up. Low and behold there was a bill for 96.00 for the diagnostic. Needless to say I was very upset when the check engine light along with the other lights came on. Air filter new gas cap new. Did almost everything I found that could cause the lights to come on. I even sprayed ether around the intake manifold, no change. Had Monroe muffler check for exhaust leak. Nothing found am I missing something or do I have to continue replacing parts. I really love my truck and would like to keep it but if I'm going to start having major problems I will unload it. Can anyone help with some answers I would be more than thankful.