Cannot get into accessory mode

I bought a used 2009 Prius. Somehow it refuses to go into accessory mode. I press the power button without stepping on the brake pedal and nothing happens. Anyone have any ideas? I wonder if this symptom is related to the fact that this car is supposedly equipped with SKS (fob has silver logo and there is a black square on driver door outside handle) but the smart key functionality does not work? (The car came with only one key fob.)

 

Yes, registered key fob is inserted when I do this. That is how I normally start the car.

 

Yes, the "key" button under the dash is turned on. I've tried both on and off positions just to make sure.

 

Thanks for the suggestions. Yes, I changed the fob battery. Since I can't get the car into ACC mode, I couldn't check the battery voltage via the display without having it be in READY mode, which meant that when I look at the battery voltage display, it reads 14.1 V, i.e., it's getting charged. So I used a volt meter to measure the battery directly with the car turned off. At that point, the reading was 12.75 V. Then I opened the doors and turned on the headlights, which dropped the reading to 11.99 V. It seems the battery is not bad.

 

I rechecked the battery after sitting overnight, and it still checks out. I also disconnected the battery for several minutes and reconnected. No change. Still cannot get into ACC mode. Other electrical systems work O.K. Lights are bright, sound and climate systems good, etc.

This might be a crazy idea, but I suspect (for various reasons) that this used to be a rental car. Could they have deliberately disabled some functionalities for whatever reason?

 

Thanks, but I know how to enter ACC mode. The car just won't do it.

 

Wait...I think I found a thread that exactly matches this symptom: No ACC mode | PriusChat. I'll have to go check if there is any suspicious aftermarket wiring installed under the dash...