P3120 after replacing I.C.E. gas engine

I just replaced the I.C.E. in my Gen 1 Prius with one from a wrecked donor with <60,000 miles vs. 250,000 on my original engine. I admit, it took me a few months to find the right donor so my Prius has been sitting for awhile.

What are the possible causes for it throwing JUST the P3120 DTC? No other codes are present. Obviously, the transaxle was fine when I pulled the old engine. So I've messed something up along the way, but what?


I carefully rotated the crankshaft while bolting the engine and transaxle together to be certain there wasn't any binding during assembly.

The code is being thrown when I turn the key to 'Start'. The HV is at about 25%. The 12v is a fully charged Optima. The dash lights and screen look normal when the key is only turned to the 'On' position.

To me, it sounds like the MG1 is preparing to crank the gas engine then it throws the code.The gas engine never turns or attempts to start.

 

Thank you! I will look up how to grid charge the HV battery. What is reasonable to pay the dealer to charge the HV batterys?

The 12v is and has been on a high quality charger with full charge and trickle functions.

I discovered I'd replaced one of the three phase connection bolts at the back of the inverter ("U" line as I recall) with a stainless steel bolt. Stainless has about 3% of the conductivity of copper. I ordered a replacement bolt at the dealer when I went in to ask about having the HV battery charged there.

Stay tuned and I'll update the thread as things progress.

Wade