I recently had a smog test indicating my tailpipe hydrocarbons were much higher than average, and the guy at the shop suggested it could be an O2 sensor going bad, which would cause my engine to run richer than normal. My fuel economy has been relatively stable over the last couple years, although it does seem to be a bit lower (maybe 1-2 mpg) since last year.
I'm averaging about 26-27 mpg on a tank (70% highway driving), with a 2000 Altima GLE (4 spd Auto with O/D). On some long distance trips I can still break the 30-31 mpg mark.
The guy at the shop says it's quite common for the O2 sensor to be degraded without the service engine light coming on (my service engine light is not on), and combined with the labor cost could be a good reason why the O2 sensor seems to be the last item on the list when it comes to vehicle maintenance.
So here's my question. Has anyone noticed a significant MPG improvement after replacing their O2 sensor? When I say significant, I mean at least a 2 MPG improvement.
Thanks.