[sidatu]

Hello,
My 2007 Honda civic has been recently giving less MPG (25 MPG / 9.5 l/100km at max - City/Highway combined), I've never had better fuel economy than this.
Its a DX Automatic with 251000 km / 156000 miles.

I just got an OBD2 scanner tool and after reading the live data,
I found out that the Upstream oxygen sensor was showing no data at all (No response), and still it didn't threw any CEL whatsoever.

I changed the spark plugs (NGK OEM recommended) just 2000 km/1250 miles ago. Air filter looks good.

The live data was as follows:

OXYGEN SENSOR 1 VOLTAGE: No response
OXYGEN SENSOR 1 FUEL/AIR: No response
FUEL TRIM (LONG) B1: -12.5%
MAF RATE (I think it was idling at normal RPM): 2g/s
OXYGEN SENSOR 2 VOLTAGE: 0.53 V

The fuel trims had a bit of variation every time I check it, but every time, it was in the negatives (Short & Long) which I believe means the ECU is removing the extra fuel.

Does this NO RESPONSE and NO CEL means a lazy oxygen sensor?

Thanks!