NF Mod/Nissan Master Tech
Join Date: Jan 2006
Location: Prospect, VA
Well, first of all, if the check engine light illuminates, i would recommend you have the problem diagnosed before you rack up another 180,000 kilometers!
P1490 indicates the ECM received an improper voltage signal from the vacuum cut valve bypass valve, which is located under and to the rear of the vehicle, not far from the coil spring. It's an electric solenoid valve that controls the flow of vacuum as part of the evaporative emissions system self-test. The usual cause is the solenoid sticks, meaning that the vacuum cut valve bypass valve should be replaced, but a short or open in the harness to it, or a poor connection in the harness connector, could set the code, as well.
The P1490 code has nothing to do with the gas sensor (I'm assuming you are referring to the exhaust gas sensor, AKA "O2 sensor?".....If so, did the update the ECM in the process as per the TSB regarding O2 sensor incidents?).