I have been getting bad gas milage on my '96. I checked the ECM and it shows 34 on the MIL. Does this mean the sensor down near the cat converter is bad or just a high reading. Why isn't my 'check engine' light on while i am driving ? I did the o2 sensor check and the MIL blinks 5 times. Does this mean that both 02 sensors are OK or just the top one ?