Front and Rear O2 Sensors

[Half Colin]

Does anyone know if there is a difference in operation between the front and rear O2 sensors?

Long story but a local garage has cocked up with our Corsa and fitted a rear sensor, that I bought but didn't have time to fit because I was going overseas, in the front position instead of the rear. On return to correct the problem they fitted a new rear in the rear position and left the front with the rear they had fitted earlier.

I know I should get my wife to take it back again but It's quite a hassle and it runs ok so if there's no technical reason why not I'm tempted to just leave it.

I've been doing some research and found that the front sensor is used to adjust the fuel mixture and the rear one is to check the cat is working - some sites also say that the rear one is heated. Some cars also use different connectors and have different cable lengths. But, for the Corsa the cable lengths and connectors are ok even though they have different part numbers and prices. Maybe the rear one costs more because it's heated?

The more I think about it the more I'm going to get the garage to fix it, but I wondered if anyone on here had any professional knowledge on how these things work.

 

[bcworkz]

O2 sensors don't work properly unless they're good and hot. They started adding heaters to them a while back so they start working correctly after cold startup much more quickly. Makes more sense to me for the forward ones to be heated as they do the engine management. Just checking the cat is less critical. This appears to be the way the N52 is set up, as there are more wires in the forward ones.

OTOH, perhaps the rears are heated in some cars because they have trouble getting hot enough on their own, whereas the forward ones should get hot on their own eventually without extra help. I suppose which logic is used depends on the specific manifold configuration, how far the cat is from it, and the goals of the car's market and design.

In other words, I can't answer your question, but more info is usually good.

If nothing else, I'd be concerned the response curves may be different between the two, affecting emissions and efficiency, even though there is no discernible difference in the running characteristics. If the wrong one was in the rear, I wouldn't worry as much.