Can you tell me it there are directions that a service technician uses to reflash the computer in a Toyota Camry. It is a 2002. We took it for service because the check engine light was on and the gas mileage had dropped significantly. I believe they were replacing the oxygen sensor, (I think they refer to it as Bank 1 but am not sure). This evidently requires reflashing of the computer. I would like to know if the technicians have directions to do this or steps they are taught. And also, approximately how long does it take to reflash the computer.

We had no reason to believe there was any problem with the battery in the car, no signs etc. It always starts right up etc. But they told us that the battery was bad and failed during the reflashing which caused the entire computer in the car to go bad. I'm thinking that if that is a possibility, that a battery failure can ruin the computer during this process, and the battery can fail with no indication that it is going bad, that there should be a first step to ensure that there is enough power in the battery to endure the reflashing process.

>Moved from Intros<

Ok, Cutis, THEEEEE first step in reflashing the ecm is hook up external battery source. A 10A trickle is just fine for this procedure.
I've seen way too many techs trust the car's battery for doing the reflash. THIS IS NOT RECOMMENDED BY TOYOTA!
The complete flash takes about an hour. They connect a laptop to your car's computer. It's name is "Techstream" (directions, steps, you asked about) It downlods by wirless internet for a specific flash through the TIS website.
This download is fed to the car's ecm. Then, a new calibration ID is entered and will change the car's drivability. Even the way it shifts.
What they did was let the votage run too low during flash. The first thing to take the hit is the ECM.

BTW, today's high tech battery testers can test it's integrity and fail it WELL before the engine cranking is ever noticed.