Prius (2004-09) :: 2006 - Hybrid System Overheats With Codes P3190 And P3191

Something in my Gen II 2006 Prius is causing a type of overheating condition in the hybrid system. The fault/error codes coming up are P3190 and P3191. If I turn the car off for 30 minutes and restart it, it runs fine for a period of time (but usually not more than a week).

I first noticed the problem a couple of months ago during my 45 mile (mostly highway) commute. While driving on the highway, I noticed that the Prius wouldn't accelerate when I stepped on the gas pedal. A couple of minutes later, my dash warning lights come on and the car started slowing down (no response to the gas pedal at this point). For a minute or so, I was able to change gears (reverse or drive) and move a little in either direction but the transmission stops responding altogether very quickly.

Dash lights that light up

Hybrid system error symbol lit up and I noticed that the hybrid battery charge level was at one purple bar.

The first time it happened, I had my car towed to the nearest Toyota dealership. The flatbed tow truck driver (to my surprise) was able to start the Prius and back it into a spot at the dealership. Some of the dash lights were no longer lit.

The dealer couldn't find anything wrong with the car except for the fact that my water pump was leaking. They replaced the water pump, cleared the error codes and drove the car around for about 45 minutes but couldn't reproduce the problem. I drove my car home.

note: this dealership replaced my hybrid battery and 'computer' (I'm sure it has a specific part name - I don't have the info) right before my warranty ran out over a year ago. I didn't have any warning lights lit up on the dash at the time but I told the master mechanic working on my car that it didn't have much power going to the wheels when I put it in reverse (I couldn't back into my driveway). After the hybrid battery and computer were replaced, I had no issues with backing into my driveway.

The same issue happened a week later. I turned the car off for 20-30 minutes, started the car and noticed that the bulk of the dash warning lights turned off so I drove it home. I took it to my local mechanic the following day. He cleaned the intake manifold, changed the spark plugs, cleared the P3190 and P3191 codes indicating that they were generic codes indicating a misfire and said that it was now running fine.

A week later the same thing happened. I did some research and brought the car back to my local mechanic and asked him to change the transmission fluid & to use the Toyota ATF WS fluid. He changed the transmission fluid (and noted that it was dirty), cleared the codes and I brought the car home. I unfortunately didn't get a sample.

We had a power failure that night so I plugged my pond aerator into the cigarette lighter to keep my koi alive and less than 2 hours later I came out to find the pondmaster ap-20 (20 watt) air pump (blows bubbles through 1/2" tubing) wasn't running and my car had shut off with the dash warning lights illuminated. I have run this little aerator for 4 days on a single tank of gas without issues in the past.