Disconnected Battery -> Reverse Beep Impossible to Disable -> Electrical System Broken?

Once upon a time, I got a 2006 Prius and disabled the reverse beep. Then, my stereo jammed, so I had it fixed. Putting the panel back together, there was a huge red triangle on the dash, and a red car outline on the MFD. Disconnecting and reconnecting the battery fixed this but reset the car, including the reverse beep.

So, far, this all makes sense. However, the kicker is that I can't disable the reverse beep again. I'm wondering if something is wrong with the car now.

Specifically, I made sure the odometer was set to ODO and not Trip A/B. Then I turned the car off, and then on with the ODO button depressed. I kept the ODO button depressed while the dashes counted down to the right and the odometer read a string of 0's briefly, and then reverted back to the normal mileage. Keeping the ODO button held down, I put the gear in reverse and then pressed park. Nothing.

I've tried variations with the seat belt on and off, the passenger seat occupied and not, the (driving) brakes on or not.

I tried getting into the diagnostic menu by holding down info and flicking the lights on and off 3 times. The menu came up. The systems were ok, except for stereo and NAV, which said "CHK." (This may actually be normal for the way it was before too, but I don't recall precisely.)

One guide suggested that if the ODO reading has been updated (whatever that means), I would have to drive around the car a bit and it should work the next time. I've driven 14 miles since reconnecting the battery, and it still doesn't work.

I really don't understand why the reverse beep disable isn't working anymore.

Is there something I did wrong? Is the car confused whether or not to allow the disable? Is the seat confused and thinks it has a passenger? Could I move the passenger seat to fix this? Is the menu saying what it should? Is my electrical system broken? Or is this normal?

 

Argh! You're right. I know that's how you turn off the oil reminder light, since I've done that more often than turning off the reverse beep. I actually thought you started it the same way but added the extra steps of putting it in reverse and then park. I didn't realize that it made a difference whether you started it held down or if you held it down after starting.

Well, it does make a difference, and you're right, and it works now.

Thanks.

PS Before I posted, I did try holding it down *after* starting the car, but I probably didn't wait the full 10 seconds. It's always longer than you think it is.