Poor fuel mileage

You have two separate issues. First let's get a new post started on the A/C issue because you are most likely low on Freon and the evaporator is freezing which is blocking the air flow. So we need to start a new post on that issue as others will not find the solution to that under this post.

https://www.2carpros.com/questions/new

As for the fuel mileage the leading cause of it is change in driving styles/trips/types of driving. I am going to assume that none of this happened and that you have been doing the same commute but the mileage just dropped.

If this is the case then we need to make sure the tires are inflated properly and confirm you are using 0W-20 oil if you are in the USA/Canada region or 5W-30 if you are anywhere else. The wrong oil will affect this.

If all of that checks out then we need to monitor the o2 sensor data and see if the exhaust is rich. Meaning there is low oxygen in the exhaust and if it is then we may have an injector issue. If they are hanging open it can cause the engine to run rich, decrease fuel mileage and eventually turn the light on but we don't need to wait for that. We can monitor them now with a scan tool and see what the fuel trims are and go from there.

Below is a chart showing what the trims should be. Thanks

Okay. That is good. You can monitor the short term fuel trim or the o2 sensor voltage. Both will give us lean or rich information. Just let me know what they are while you driving a steady speed. They are going to change as you give it gas and take it away so we want steady driving to get good numbers on the sensor voltage. The short term will be an average so it won't vary as much.

Okay. That is conflicting information so I think that is the issue. What this is telling you is that the long term is saying the exhaust is lean and the PCM should add more fuel. The long term fuel trim is like the overall long term performance of the engine. The short term is what the exhaust is reading at that very moment.

So the short term is telling you that it is rich and the exhaust should go lean to correct this. However, the long term is saying the opposite.

If it were me, I would replace the o2 sensors and then drive it about 150 miles to allow the PCM to relearn the new sensors and track the mileage as you go. I suspect it will get better as you drive.

That is your emissions monitor data. Basically that is a snap shot in time. If the long term fuel trim was positive and the short term was staying negative then you have an issue there. The long term fuel trim is a better representation of what is happening because that is a larger picture as it takes a while to change that.