U0100 and U029A Prius V Fault Codes

Have you attempted maintenance mode? That is a mode which forces the engine to run non-stop, until you turn it off. This is helpful when changing the coolant, to get the engine hot enough to force the cooling fans on.

Warning: let some other folks comment on how wise it would be to put the car into "maintenance mode", before you try it.

I have never transplanted an engine in my Prius. This is background information, that may save you time if you decide it is prudent to try forcing your engine to run in "maintenance mode". It is possible to do damage that I am not aware of.

Anyway, the video showing how to put your Prius into "maintenance mode" assumed you have a different instrument cluster that has a small LCD screen on it. When you successfully get the car into "maintenance mode" on a car with the LCD screen, the words "maintenance mode" appear on that screen. You and I don't have that LCD screen, so how do you do it? Note that my 2017 Prius V four has the LCD panel in the instrument cluster.

Here is the script I wrote for a video I never got around to filming. It describes how to get "maintenance mode" on a Prius without the LCD panel to tell you that you got into "maintenance mode".

Inspection / Maintenance Mode PriusV

Hi my name is Don AKA GromitToo and today I am going to show you how to put a 2012-2014 Prius V into Inspection Mode, sometimes called Maintenance mode.

I recently had to change the coolant on my 2013 Prius V. I found a really good video by NutsAboutBolts about changing the coolant on his 2012 Gen3 Prius. But I ran into trouble when I tried following his steps to put my Prius V into Inspection Mode, and got totally confused. While the Prius V years 2012 to 2014 are almost the same as a regular Gen 3 Prius, years 2010 - 2015, the instrument cluster is quite different. Hence the confusion, and this video.

First of all, we are going to start with the car off, and your right foot on the floor. You also need to have the parking brake on. Once we get started, your foot will either be pumping the gas pedal to the floor two times, or your foot will be on the brake. You will do three sets of pumping the gas pedal two times. The whole procedure needs to be completed in under about 30 seconds for it to work.

OK, let's begin, car off, Parking brake set, and our right foot on the floor.

- Press the "power" button two times to put the car into Auxiliary mode. Most of the instrument panel will be lit up.
- Next Press the gas pedal to the floor two times, and move your foot to the brake. (First time)
- Now move the gearshift lever into "Neutral". Make sure you see the indicator on the cluster move from P to N.
- Next Press the gas pedal to the floor two times, and return your foot to the brake (Second Time)
- Now Press the Park button .
- For the final time, Press the gas pedal to the floor two times, and return your foot to the brake.
- Note that at this moment, the Hybrid indicator on the far right is blinking, Also, the Traction Control light just to the right of the "ready" light will be on steady. This means we are almost done.
- Foot still on the brake, Press the Power button one time. The ready light will appear..

At this point, the engine will start immediately, if it was not already running. The Traction Control light should be on steady, and the lonely Hybrid Warning light will be blinking.​

The Internal Combustion Engine will keep running until you hit the power button again. The traction battery will not charge. While, it is possible to drive the car in "Inspection" mode, Toyota does not recommend it, unless it is specifically needed for a test. Driving can cause damage to the hybrid system.

It takes over a half hour of engine run time to get the whole cooling system hot enough to turn the cooling fans on. This is a required step while changing your coolant.​

 

Do you mean ECM or Inverter?
How did you get the car started without the Traction Battery?

 

What are you using to read codes?

Does it show which codes are current, pending, historical, and permanent?

Does it show which ECU each code came from?

'Permanent' codes are kind of misnamed: they aren't stuck there forever, but you can't just clear them. They will be around until you get the car running and it has a chance to complete the corresponding monitor tests and convince itself those problems have been fixed. Then the 'permanent' codes go away by themselves.

Knowing which ECU each code came from is important, especially for communication (Uxxxx) codes. The code tells you which ECU the complaining ECU isn't able to talk to, but of course to troubleshoot a communication problem you also need to know which ECU is doing the complaining.

If you use Techstream to read codes, you will see all the needed information.

 

My Traction Battery Charges when in Maintenance Mode.

 

Did you ever find out a solution to this?