GX oxygen sensor heater failure

I had a similar issue with my GX. Same symptoms: check engine light, fuel economy tanked, and the code pointed to the O2 sensor heater circuit. I'd suggest checking the wiring harness and connector for the sensor. Corrosion or a loose connection can definitely cause that heater circuit to fail. Did you try testing the sensor itself?

Good call on the wiring harness, I'll give that a closer look. When you say 'testing the sensor,' what exactly did you do? I have a multimeter, but I'm not entirely sure what readings I should be looking for to confirm a faulty heater element. Any tips?

Yeah, the heater element has a specific resistance range. You can disconnect the sensor and use your multimeter to check the resistance across the heater element terminals. If it's way out of spec (usually open circuit), the heater's probably shot. Honestly, if you're not comfortable with that, a shop can diagnose it pretty quickly. It could be as simple as a bad sensor, or something upstream causing the issue.

Thanks a bunch for the advice! It turns out the connector was indeed corroded. Cleaned it up, but the sensor was still dead. Ended up replacing it – cost me about 95€ with a new Bosch sensor. Problem solved, check engine light is gone, and fuel economy is back to normal. I'm grateful for your help!