2005 Prius OBD and communication issues

might be a good idea to get a prius aware scanner, and relook at the trouble codes.

 

First check the OBD fuse in the interior fuse panel.

That said, many scanners will not work properly in the Prius.
What scanners are you using? Brand/model.

An elm 327 OBDII in conjunction with the the Android version of the Torque Pro app may help.

Even better would be a minivci dongle in conjunction with an xp laptop running the techstream software.

Without the right tools you'll never see what is really going on.

 

There are no codes logged so why are you trying to pull codes?

Many OBD's are not hybrid capable. Especially the ones your using.

 

The third scanner most probably caused the Uxxxx codes as it may not be able to communicate with the correct protocol.

Depending whether the scanners have the correct PID extensions to talk all the Prius ECUs, they may not be able to "see" all the DTCs set and will be of limited use.

 

I had the same issue. My 2007 Prius OBD wouldn't communicate with the state emissions equipment. The 7.5a OBD fuse under the dash was fine, and I had no idea what to do. I went to a different emissions location, and it passed with flying colors.

 

Old topic, but I'll drop a reply anyway.

My Prius' dash lit up with idiot lights for brakes, check-engine, and eventually even the Red Triangle of Death.
DTC diagnostic trouble codes U0100, U0111, U0293. These all indicate problems communicating with the engine control computer.
Other posts here on PriusChat said this could all be due to a weak 12V battery. Sure enough, 11.7 volts with the car in accessory mode. I might be calling it by the wrong name ... push the Power button with your foot OFF the brake, gets it in this booted-up but NOT 'Ready' mode.

OK, 11.7 volts is not good. Replaced the 12V battery. Of course replacing the battery involves several minutes of having no battery connected, and that is enough to clear all the DTCs.
Once the car got properly started, no more idiot lights on the panel. A hundred miles or so later, still nothing wrong.

This combination of U0100, U0111, U0293 can all be caused by a bad 12V battery.

I'll say anything under 12V in accessory mode means Definitely You Gotta Replace That 12V Battery.

Be careful not to be misled by your Prius. If it gets booted up into Ready mode (foot on the brake when pressing Power button) the voltage goes to about 14.1V and you can't see the true battery voltage.

 

It's great you got your car fixed, but the conclusions you have drawn are not really cause and effect.

I and many others have operated Prii with the 12 V battery at 11.8 V or less for quite some time and never had Uxxxx codes.

It is more likely you cleared the codes when you changed the battery and the conditions that set the code in the first place no longer exist.

The only thing you could really say in this case is that the battery needs to be charged up. If you enter ACC mode and you see 11.x V and then press the power button once more (with your foot still off the brake pedal) to go to IG-ON and you still hold 11.x volts, then you need to charge the battery. If you do not hold voltage and drop quickly to below 10.5 V, then you need to replace the battery.