after installed new a/f sensor code p0174 appeared in 02 sienna 6cyl. 3.0l

Question

checked vacuum and exhaused leaks, none found
vacuum gage is on 20in. at idle steady
car has 95000 miles, runs well and is quiet
what could be the problem
how to get ecm softwear update if required

Answer 1

P0174

Fuel trim lean Bank 2

There is no ECM update, when you set a lean code condition there is more air to fuel mixture, the engine will run good, what the ECM is doing is compensating for the lean code by adding more fuel to the second bank for correction, Check the sparkplug condition and if worn have it replaced, do also a MAF (mass airflow ) cleaning , a MAF that is dirty will set a lean code condition.