First off, my 99 Camry is a GREAT car. It runs super reliably, and had never seen a trouble code until I all of a sudden got multiple codes;

P0125 (insufficient coolant temperature for closed loop fuel control), P0171 (system too lean, Bank1) P1130, 33, and 35 (all are Manufacturer control)

It's amazing to me that instead of just having a single code that says... Hey! your upstream air/fuel sensor (which looks exactly like an 02, but works a bit differently) is on the fritz, so change it. Instead, you need to try to figure out what the codes are alluding to. It's so stupid. Thankfully, there's tons of people on the internet that are dying to tell you what it all means.

Instead of going through Toyota and paying well over $300. for the same Denso sensor, I just punched in the part number into Amazon's search engine and saved more than $200. for the exact same part, and I mean EXACT! I installed it on December 19, 2019 and here it is July 7, 2020 and it has worked perfectly. Install was super easy too.

I believe I know why the air/fuel sensor went bad. I purchased the car used with 89K in Nov 2018. I know from the previous owner and the records that the car was only serviced at the Toyota dealer with conventional oil. I wanted to upgrade to synthetic oil which is not always as smooth going as you might think. I changed over to Walmart's SuperTech full synthetic 5W/20 winter oil. Almost immediately, I would see a puff of smoke at cold start-up. The engine wasn't using oil, just a little puff every morning, so I wasn't concerned. However, that smoke may have led to pre-mature failure of the sensor. I have now switched to Pennzoil Platinum 5W/30 and the puff of smoke has discontinued. All is great with my engine now. I LOVE this car!!!

Check engine light came on and car would not pass emissions due to a bad O2 sensor that was located under the driver's seat, under the car. The O2 sensor could not be detached from the exhaust pipe because it had either rusted or fused together. Several people tried everything possible to detach it but it was not possible without breaking or torquing the pipe. The exhaust pipe had to be cut off in a section and a new piece recreated with an opening to reattach a new O2 sensor, then re-welded back together so the car would pass emissions. It was a big pain in the a$$ for a repair that should have been very simple.