Running rich won't cause it to run cold and limp mode is not activated by the rear O2 sensors to the best of my knowledge.

 

so its running just below half? thats where mine is all the time...

 

Yeah I don't think his car is really running cold. Mine runs just under half as well. But yes a bad O2 sensor will cause the car to go into limp mode. Every OBII(I) car will do that. With the sensor not working correctly, the car can not get a correct O2 reading and the car will start running rich.

 

how hard is it to replace and where exactly is the o2 sensor, im not familiar with smaller engines like this.

 

The rear O2 sensors do not monitor rich/lean, so there is no need for the computer to go in limp. Front O2 sensors? Ok.

The O2 sensors are on your exhaust manifold. One on each where the the three exhaust pipes collect into one, and another after the catalytic convertor in the exhaust manifold (those are easier seen under the vehicle).

For terminology purposes, the rear cylinder bank is called bank one (because it has cylinder #1), so, sensors on that would be Bank 1, Sensor 1 (upstream) and Bank 1, Sensor 2 (downstream). Likewise on the bank toward the bumper, it would be Bank 2, Sensor 1 and Bank 2, Sensor 2.

 

ok, well i gotta wait and see what the dealer says tomorrow.

 

Really, I hate to show up people, but here is a great article about how o2 sensor works. How o2 sensor works. The lower sensor works just the same and it important for the all the o2 sensor readings. If one does not work it will cause a car to go into "limp mode," because it can not get the correct readings to establish the correct air/fuel mixture. The lower sensor is use to check if the car is running to rich and fuel is making out the exhaust. Many people think this sensor is just used to figure out if your catalytic converter is working or not. That is not the reason the bottom o2 sensor is placed there. It is true that most of the time if your cat is not working, you will get a reading for a bad o2 sensor because it is either gummed from the cat or because the cat is not flitering out the correct gasses.

My guess is once the dealership replaces that sensor, your car will be running right and your miles per gallon will improve. I had the same thing happen to my '97 Neon.

 

well turns out its a catalyitic converter effeciency code... not O2. Meadowbrook dodge is the WORST dealership ever...