engine codes, p3105, p3115

Any chance you could add some details? How long have you had the car? How long would you like to have the car? What's your overall background in working on cars, or in working safely around typical Prius voltages (around 300 volts)?

For any serious work around a Prius, I'd say lose the Chilton's. The factory manuals can be downloaded from techinfo.toyota.com on a $15 subscription, and unlike the fakebooks, they will actually tell you stuff you need to know about your car. In particular, when you look up your codes in the manual, they will have page numbers next to them, where you will find whole troubleshooting procedures you can use to home in on the problem.

The relay you're referring to is inside the main battery case, and that's a high-voltage environment even when the car is off. If you look at absolutely nothing else (which I don't recommend), at the very least, see if you can search up a copy of the "SSC 40G" battery service campaign instructions. (Not the short announcement letter, the instructions, about a 56 page pdf.) They will give you a good overview of working inside the battery and how to do it safely.

As for how to reconstitute a dead or dying battery, in cases where that might be possible, there are a lot of threads in this forum about that, and you'll probably find a few hours finding and reading those to be time well spent.

Good luck,
-Chap

 

Let me suggest:

1. Disconnect 12 V battery (the ground wire)
2. Measure 12 V battery voltage:
   1. 12.85 V - perfect, 11.9 V usable
   2. < 11.9 V Uh OH! put on charger
3. Connect 12 V battery and try to start car

Now you can begin problem diagnosis. Without a good 12 V battery, nothing is to be trusted. Disconnecting it for 30 seconds wipes all code. When you try to start again, we will get the current, fresh codes. This is where we start.

If car starts, measure the running 12 V. If it is 13.8-13.9 V, the 12 V circuit is charging and we can begin running car diagnosis. If it does not start, we can begin non-running car diagnosis.

We'll wait till you get there.

Bob Wilson

 

DTC P3105 means a communications error between the traction battery ECU and the hybrid vehicle ECU. As you know, P3115 means a problem with one of the three system main relays located in the traction battery enclosure.

As previously suggested, you or your mechanic need to subscribe to techinfo.toyota.com to obtain factory repair manual info to help you address these problems.

 

With respect, I agree with Patrick after the 12V system is checked. A marginal 12V circuit can cause a lot of misleading codes. Once we see solid 12V, read the codes and follow the Toyota fault-code instructions in Volume 1.

Bob Wilson

 

When you say you "did everything that was recommended" does that mean you really did look up your codes in the real manual and follow the specific testing and troubleshooting steps there?

One of the hardest notions to get across to newcomers is that when the car's computer gives a code x and you see a one-liner code listing that says x means system main relay, that does not mean the computer is telling you to change the system main relay.

All it means is, the computer is telling you that somewhere in its entire control and monitoring feedback loop involving the main relay, something isn't right. Your mission is to find out what isn't right in that whole subsystem, then fix it. The troubleshooting steps in the manual will be invaluable for that.

-Chap