2005 Prius - after ECU replacement, car won't turn off... electrical problems

Huge thank you in advance for trying to help keep my beloved 2005 prius alive.

My saga begins when on a cold day in Feb (but not that cold) my car wouldn't start. I thought somehow the battery died, and when I came back to try and jump it a couple days later it just turned on, no issue. Weird, but everything seemed fine for another couple weeks, including a visit to a shop to get an oil change and replace a belt - the shop never mentioned any intermittent starting issues so I assume the car behaved fine during that time.

A day or two later, I got the large red caution triangle light on dash. My Prius is dead and stuck at a friend's house. I could turn the car on and start the engine but not put it in drive. I checked the codes and the car told me that it could not communicate with the car computer. I took a gamble on the integrity of the wiring and decided to replace the ECU with one that I bought on FlagshipOne. I disassembled my dashboard to reach the ECU, switched it out, and reassembled everything. In the process of course, I left all my doors open and lights on and drained my 12 V battery.

Using a friend's external battery jumper thingy, I was able to turn the car on. I checked the OBD reader again and my computer code was cleared. I put the car in drive and moved forward 6 inches, very excited that it was working. Alas, I turned the car off again and couldn't restart it with that same external battery. There were again some weird dash lights that didn't seem consistent with anything I was doing, but I thought it was because my battery was very dead and wasn't getting consistent current from the external jumper battery (which itself would turn on and off). It was getting late, so I decided to go home and take my 12 V battery home with me and trickle charge it.

When putting the 12 V battery back in, as soon as I connected the positive terminal, the car turned on, meaning all the dash lights not the engine. From this point on, I was not able to get the car to do anything - pushing the power button does nothing, taking the parking brake off doesn't make that "brake" light go off, the only dash light that will respond to anything is turning the headlights on and off. Certainly can't put it in drive, and unfortunately I didn't check the codes again that night. I unplugged the 12 V battery to turn the car off, and that is where I have left the car, still sitting on my friend's street.

Has anyone seen something like this before? Any advice would be so appreciated!

 

Hi all and thanks for your attention - I replaced the ECM, the one that controls fuel injection etc. I used a Zurich ZR4 obd2 reader, which told me "U0100: lost communication with ECM/PCM 'A' ". I very well might need to use a different scanner, thank you for the advice. As-is, I am unable to power cycle the vehicle except by connecting/disconnecting the positive terminal of the battery.

 

I have not checked fuses - thank you I will look into that! My catalytic converter was stolen 3 years ago (sigh).

 

To update the thread: I checked all my fuses yesterday and they seem fine. Now going to get the fancier scanner - thanks everyone!

 

Another update, the new OBD scanner works a lot better. Unfortunately, a lot of codes, but what did I expect?

U0121 - lost communication with anti-lock brake system control module
U0073 - Control module communication bus off
U0123 - Lost communication with the yaw rate sensor module
U0124 - Lost communication with lateral acceleration sensor module
U0126 - Lost communication with steering angle sensor module

Does anyone know if all of these codes could come from, say, the same connector not being plugged in all the way?

The symptoms are quite bizarre - I can still only turn the car off by unplugging the positive terminal of my battery.

Any thoughts would be appreciated!

 

Thank you both.

MAX2 - thank you for linking the wiring diagram, I have a multimeter and I'll take a look at that with my friend who has a lot more experience than I do.

vvillovv - yes, differently from the car in the post that MAX2 linked, I can turn my car on (though not the engine anymore) by plugging in the 12 V battery, but then nothing on the dash will respond except the headlights. To turn the car off, I have to disconnect the 12 V. I can try trickle charging the 12 V and putting the original ECU back in, thank you.

 

Thanks for linking the thread - I see one comment referring to the inability to turn the car off when the CM is bad (or maybe I just need to hold down the power button), but just to confirm, my dash never went dark. Quite the opposite: all the dash lights go on when I plug in the battery. I'll look into this fix if you still think it's the CM!

 

Please forgive this horrible photo - this was the last photo I took of the dash when I connected the battery. So all the green lights come on even though you can't see them in the photo, along with the orange lights, but no red triangle. The parking brake light is on, but if I take the parking brake off, the light doesn't go off. Headlight indicator does come off and on though.

 

Hi Prius Friends, another update:

To order a new combination meter, I wanted to get the exact milage on my car, so yesterday afternoon I made the trek to my car which to this point has been stuck at my friend's house. It has been warmer the last few days which could have played a role -- this time when I connected my battery, I got the car out of accessory mode and was able to actually put it in drive! So the exciting news is that I was able to take it home and park it in front of my house.

The confusing news is that I received an email back from Texas Hybrid Batteries regarding ordering a new combination meter from them. Matt said, "nothing you've described sounds like a combo meter issue in any way." I believe he is saying this because in his experience, issues with the combination meter always come with a dash that has gone completely dark. "When we refer to the display not working it's not just a part of it, it's the whole thing. The car will be on and drivable but the whole dash will be black. No speedometer, gas gauge, odometer, or shift indicator."

If my issue is not the combination meter, it is likely a "damaged wire, weak relay, corroded connector, etc" that will be hard to find, so I just wanted to ask the folks here who were confident about the combination meter: In the cars whose combination meters you have fixed, were there any like mine where the dash lights still come on, they are just unresponsive? Or are the only shared symptoms the temperature dependence and the power button no longer turning the car off?


Thank you!