My 99 GS 400 is having a problem with O2 sensors. The check engine light comes on with PO171 Bank 1 code. I changed out all the O2 sensors, But the check engine light won't go off and it's still showing the same code, PO171 bank 1. I also failed the smoke check. Any advise and suggestion is Greatly appreciate. Thank you.

 

Have you reset your ECU by removing the negative terminal from the battery for a half hour? May help

 

Some of the other things are:
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leakage on exhaust system
Open short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit
Heated oxygen sensor (bank 1, 2 sensor 1)
ECM

Did you reset your CEL or give it time to cycle itself off?

 

Make sure the oxygen sensor is from Denso. And reset the light.