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Toyotapro, ASE master tech
Category: Toyota
Satisfied Customers: 9974
Experience:  ASE Certified, 10+ years Lexus and Toyota Certified
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The other day I used my tow dolly with my Prius for the first

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The other day I used my tow dolly with my Prius for the first time. After I drove the Prius off the dolly, my MFD, radio, Park Button light, and accessory ports no longer worked. I don't believe the MFD itself is the problem (although the Prius is a 2004, the MFD is actually model 081, the latest one, so it's probably been changed already?), and that wouldn't likely explain the power port failure. I have checked all the fuses (the accessory port fuses are fine), to no avail. Is there a main power lead or something I can check?

Hello and thank you for using just answer!

You said it was on a tow just the front 2 wheels were off the ground correct?

Was anything plugged into the Prius while it was being towed or did you have external lights held to the car from your tow vehicle?

Customer: replied 7 years ago.
Just 2 wheels off the ground, yes. As far as I know, this is a valid way to tow the vehicle. Nothing else plugged into the vehicle. I use the dolly lights, as well as magnetic tow lights.

Interesting. I assume you had the keys OUT of the car so nothing could power up correct?

Have you checked the battery and also the fuses yet?

Any hybrid warning lights or check engine lights on when is "ready" mode?

Customer: replied 7 years ago.

I did have some extraneous warning events such as ABS, !, etc., but they went out shortly after the car was started...... I'm wondering about the auxiliary battery? I have checked the fuses and I can't seem to find a blown one. I have an appointment with Toyota tomorrow, but they are $115 per hour :(


I have to step out for about 10 minutes, so there will be a short delay in my next response....

That is ok, I will be monitoring here for the next couple hours.

I would check all fuses here first, I assume you know there are 2 fuse boxes correct? There is the one behind the driver headlamp under the hood and then there is the one under the drivers side dash behind where the hood release handle is at, you need to check all fuses here first.

The second thing I would have checked is the auxilary battery, these AGM batteries can really screw with the electronics when the battery is nearly dead.

Customer: replied 7 years ago.

yup, I am aware of the 2 fuse boxes (3 actually :) - the one in the back ).... I have checked all fuses, but I will check them again.


I am very aware of the anomolies of AGM Batteries. In addition to having a Ph.D. in Aerospace Engineering, I am also a master certified RV technician, and AGM are the preferred power supply of choice there :)



very good.

The third in the back I did not mention because it is basically the main power source supply, if those maxi fuses were an issue then you would have bigger problems with the car.

The AGM batteries work in the Prius a little different then they would in an RV because yoru Prius has a acdc converter and when the voltages spike around it can shut every thing down.

Test that AGM battery and also disconnect the battery for about 10 minutes to completely reset the multiplex communication system and retest the car.

If it needs a batttery they are about $130 at your dealer.

Toyotapro and 2 other Toyota Specialists are ready to help you
Customer: replied 7 years ago.

I know it wouldn't be the main breakers in the back, but there ARE 3 fuse boxes, which was my only point :)


I will test the battery for sure, and I was going to do that before I contacted you, but I just wondered if there was a power harness or something that I was missing...


I dunno, I've seen some pretty freaky things happen to coach batteries when the converter flips out :) :)


is the battery relatively easy to access?

Battery access is easy, just pull out the spare tire and the surrounding panels, it sits on the fender in the back cargo area passenger side.
Customer: replied 7 years ago.

Okay, I'll go ahead and check that, thanks.....


Any other ideas? Do you agree that it's probably not the MFD?


Most likely not the display, if that was the issue you would not have those other symptoms as well, the issue you describe is a power source issue.

We have seen the IG1 relays freeze on these but it's too warm out right now for that to be an issue.

Customer: replied 7 years ago.

what about the 30A relay marked "Power" on the front of the body ECU? If the battery tests okay, is it worth pulling the fuse box relays individually and checking them (the related ones of course)


How do you know it's not really cold where I live.... I do live in Canada after all :)..... Just kidding, it's about 23 degrees C today (well over 70F)


Yes, at first I wondered if it might be the MFD because I'm a pessimist and it's a 2004, but then I thought about the symptoms and realized it's likely a power issue, but that would normally point to a fuse....... or a bad AGM :)

I know you are an engineering genius so your mind works much different then mine and you can easily overcomplicate this when the problem is simple but don;t get ahead of yourself.

You would have to have a major short for one of those 30 amp power fuses to blow, it that was the case then you would have bigger issues. Follow what we discussed above first.

You seem paranoid about the displays for some reason......I am the hybrid specialist at my dealer and honestly I just have not seen issues on the generation 2 prius displays.....generation 1 was a piece of junk but these are actually good cars.

( the odometer does max out at 299,999 miles I did find out however.....)

Customer: replied 7 years ago.

Well, I don't know about genius, but I guess you have to analyze everything in order to design moon landers and space vehicles and the like :) Takes a different thought process for sure..... I'm great at troubleshooting complex systems, but do tend to overanalyze more simple ones sometimes.... but not always..... this one I obviously did....


Alright, I will place even money on the battery and will check it tomorrow. I might as well let the dealership replace it I guess.


thanks for your help! :)