Originally Posted By: JC1
Originally Posted By: Leo99
Gas cap or O2 sensor.
+1. I've experienced both. Can't recall what code came up in the caravan for the gas cap. In the sienna P0420 would come up every few weeks. A cheap aftermarket cat fixed that.
What's weird is that my '99 Camry had a dead O2 sensor that I only figured out when I decided to use Torq to watch O2 signals. I thought mpg was a bit low, so what the heck, let's see what the sensors are doing. Huh, why is the rear O2 flatlined? Read zero volts while the front one was fine. Looked up what to get, went on Amazon, ordered a sensor. Took a few days to come in, then had to wait for the weekend. Probably a couple hundred miles and several starts before I changed the sensor, and who knows when it had died. Never set a CEL. I should try leaving the gas cap off and see what it does.
I did have a vacuum valve switch of some sort (EGR related, common issue on this Camry) that threw a code. Pain to get to. Pulled it off, rapped it on the fender, gave it a good talking to and reinstalled. It's behaved ever since.