Code P2112 - my erroneous troubleshooting experience

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Richard Ake, Aug 23, 2018.

  1. Richard Ake

    Richard Ake Junior Member

    May 10, 2013
    Wichita, KS, USA
    2005 Prius
    I bought a '05 Prius that needed an engine (had a hole in the upper oil pan below the #4 journal). I installed an engine and transaxle out of my wrecked '05 (front end damage). I drove the car 400 miles without any issues, then one day I stopped at the store on the way home, and about 1 mile after leaving the store, the CEL illuminated followed by the Master Warning, the MDF indicated "! problem" and I noticed the traction battery was drained. The car lost power and I pulled into a parking lot. I guessed that perhaps the traction battery was not charging because it was too hot, so I removed the interior cover from the 12V battery and felt the outlet of the traction battery cooling duct to see how much air was coming out of the battery. There was very little air movement, but I had not checked this while it was operating normally, so I had no point of reference. I decided there was insufficient airflow to cool the traction battery, so I removed the storage cover and storage tray to allow more air to get the battery and allow it to cool. After a few attempts, the car began operating normally, so I turned the AC on MAX COOL and drove 10 miles home without any issues.

    My Bluetooth code reader is dead, so I used a cheap generic code reader and got the code "P2112 - Throttle Actuator Control System Stuck Closed" I presumed that the generic code reader was unable to read Prius specific traction battery codes and that the P2112 code was a symptom of the hot battery. I pulled the interior and checked the traction battery fan, it was spinning but it was very dirty and had a leaf stuck in it. I removed the fan, cleaned it, and reinstalled it. Everything seemed to be operating correctly, so I put everything back together. I removed the traction battery fan from the wrecked car and put it in the new car to carry around as a spare, just in case.

    The car drove fine the next morning, but I needed to use it an hour later, and the issue returned. I concluded that there was a pattern of the car operating normally from a cold start but having the issue after a warm start. I presumed that the traction battery was getting warm while driving, and then heat soaking itself while the car was parked. Once again removing the interior off of the traction battery and turning the AC on MAX COOL resolved the issue and I was able to drive the car about 40 miles to my destination, where I swapped the traction battery fan with the spare.

    After a few hours, I needed to drive the car again, and the issue recurred with the spare fan installed. Once again removing the interior off of the traction battery and turning the AC on MAX COOL resolved the issue and I was able to drive the car home. I checked the codes again and once again got the P2112 code. So I pulled the throttle body off the car and removed the plastic cover that covers the throttle motor. I found a piece of plastic had broken off the inside of the cover and was caught behind the throttle position sensor drive. The plastic would occasionally act as a ratchet, allowing the throttle to close but not open. See photo below...


    Cold start vs. hot start was a coincidence. The P2112 code was true. The engine could not throttle up and charge the traction battery. Driving the car on the traction battery alone quickly depleted it. Pulling the interior was a placebo. Restarting the ICE would jar things around enough to dislodge the plastic occasionally. Once dislodged, putting the AC on MAX COOL with a drained battery was keeping the ICE running above idle, since it was recharging the traction battery, powering the AC, and propelling the car. Keeping the ICE above idle changed the position of the throttle position sensor drive contact with the plastic and would help hold it away from the gear...

    One symptom that I was ignoring was occasionally when the car should have been getting only 50-60 MPG it was displaying 99 MPG. This was because the ICE was locked at idle and I was driving on the traction battery mainly. But the plastic would dislodge and the car would return to normal operation.

    Removed the throttle body from the engine with a hole in the block and installed it on the new car. Car drives great now...