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New Oxygen Sensor

I recently replaced the O2 sensor (before the converter) on my 1998 Volvo V70 XC. The car has 100K miles and runs beautifully. Before changing the O2 sensor, I was averaging around 24 mpg. Since putting in the new Bosch sensor (identical to the one I removed from the car), my mileage has dropped to around 15 mpg. My driving habits have not changed. I’ve heard that maybe the onboard computer needs to be reset in order to have the new sensor work properly. Any ideas or suggestions would be appreciated. I’m afraid I just got a bad part, but I’m guessing there are plenty of people out there who know a whole lot more than I do. Thanks in advance. Chris Edwards

Sounds like you got a bad sensor. An O2 sensor is actually a “No oxygen sensor”, that is, its signal is high when the mixture is rich, Sounds like yours isn’t reacting to the rich mixture. Maybe make sure you have the plug plugged in well…Any check engine light on?

The computer has what is called ‘mixture adaptation’ that should take care of itself with a good sensor.

earl, thanks for the response. I haven’t got any check engine lights on, and the OBDII shows no codes, so I think you’re right… it must be a bad sensor. Do you have any opinion of Bosch sensors? I was also looking into an SNG sensor.

Try this. Disconnect the positive battery cable from the positive terminal. Wait about 5 minutes. Re-connect the battery/cable. That should re-set the computer. You’ll need to re-set the clock and radio, but what the hey. Cheaper, quicker and cleaner than changing out another Oxygen sensor, eh? Just make sure that the vehicle starts. When you do your daily cruise, re-check your gas mileage. If you own your own OBD-II equipment, check and see if any new codes have shown up. If not, and you’re still getting crappy mileage, back to head scratching time trying to figure it out.

Thanks. I’ll give it a try.

I also got a bad Botched sensor for my Toyota. The car would not pass emissions, and nearly drove me crazy. I paid a shop $300 to tell me it was a bad O2 sensor. A new one from Toyota fixed the problem, and it passed emissions right away.

some NEW O2 sensors read opposite of normal thinking, two diff types of strategy.