Code PO171, fuel consumption high?

It doesn't look like it. I checked the Cat, 50 degrees difference between inlet and outlet. Here's an in tank filter. See photo.

That's what I thought also. At least Toyota gives an access port under the back seat. I'm sure it needs to be changed but I don't think it's the cause of the PO125. It could be causing the lean condition making the computer think the engine needs more gas?

I just replaced the thermostat. It runs at 90 degrees C. No coolant loss. I had put in a new temperature sensor, but the results were the same, so I put my factory one back in. Fans come on normally, never overheats. The temperature stays just below midway on gauge. I traced the ECT wires and checked for continuity all the way to the ECM. The brown (ground) and white wires go to the ECM. The yellow/green one goes up under the dash somewhere. Do you know which wires is the power and which is the signal? Also where does the yellow/green wire go?

It has three wires. The colors I mentioned. Brown appears to be ground. When I connect my test light to the positive of the battery and probe the brown wire it lights up. Maybe the ECT is failed.

I don't know what to say other than this has the three wires I mentioned and the brown and white go to the ECM directly, but the yellow/green goes under the dash? My buddy, another mechanic, said the upstream O2 sensor was failing and causing the downstream sensor to act erratically. 2008 Highlander. I'm just going to drive it and see if a PO171 code will come for injectors. Grasping at straws.

I'm going to try the upstream O2 sensor because believe it or not it's listed as a heated O2 sensor not an air/fuel sensor.

I replaced the upstream sensor and got the CL on live data. Still waiting for the downstream one I just bought, which is a genuine Denso. Finally, I can put my dash and console back together. Lol. One of the black wires was bare and frayed, quite possibly shorting out. The gasket was blown out also so that was probably the buzzing noise I heard. I should have spotted this earlier. C'est la vie.