Anyone want to help with a Ford Focus problem?

I am working on my sisters focus: it has a really rough idle and doesnt accelerate worth a crap. It has two DTC's -

P0136 - 02 Sensor Circuit Malfunction (Bank I Sensor 2)
P01131 - Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1

I have replaced the rear 02 sensor, plugs, wires, and fuel filter. It was recently in an accident and when the tech put it back together the air intake box and tubes were completely loose. At first I thought that was the problem, but nothing seems to work.... Does anyone have any ideas?

My 2000 Focass threw that code when I accidentally hit the front o2 with a wrench, and broke the internal guts all apart. Replaced it, and it was fine. Try checking the connection on the front o2 sensor facing the radiator right on the back of the cat.

year, 2V or 4V engine ?

Yea front o2 you did the wrong 1 or just missed maybe someone else guessed

+1 for front O2 sensor. Its the front ones that will give you the trouble.

IMO, replace the troubled sensor with the new one you put in the back and put the old rear one back in where you took it out.

You can't do that, because they are two different sensors. The connectors should even be different.

so you are saying that bank one, sensor 2 is the 02 sensor off the exhaust manifold, NOT the aftercat sensor? I figured for sure the sensor 2 would be that one.... thats how it is on our cars anyways.

I will look at replacing it today. I have a couple laying around for my old mustang... I bet they are the same thing.. we will see! If not, I will return the other one for the correct one.

Its a 2000 Focus ZX3, 16v

P01131 - Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1

That code is for the front o2, since it says Upstream Heated. You technically have codes for both sensors. You can try doing the front o2, because it is critical for that to run right. I've had to gut the cat on 4 Foci due to them melting and clogging up; you might also want to look into that.


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No, even in our cars....thats the front 02s. The rear 02s are not looking for a rich or lean condition...only oxygen content to check how the cats are functioning. thats why they are different part #s

Yeah, ford put 4 different connectors on the car for no reason. All the O2 sensors are the same and all you have to do is cut a small plastic strip off the connector and you can use them anywhere. For example, When you buy New ones form Bosch they give you a generic connector that will fit anywhere.

I was sure a heated upstream was different than a downstream one, but I could be wrong. I know that on my Focass, the upstream was a 4 wire, and the downstream was 3. I might have that mixed up, but there was a difference for sure.

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