Fixing Prius Mouse Damage

by Ben N on October 1, 2018

Well, it was a lot of work, but it’s done. I’ve repaired all the mouse damage in our 2004 Prius, and it’s working perfectly again!

After our last post, I looked around for a replacement wire harness, and found one on eBay, but with a number of other components in a Prius pack and at a cost of $101. I couldn’t find it anywhere else, so I bit the bullet and ordered. A few hours later, a friend, Ned, ┬áposted on social media “Is THIS what you need?” – Showing exactly the cable I needed. Ned boxed it up and mailed it to me.

Although I tried cancelling my eBay order, the seller never responded, and both packages showed up at the same time. I used the free wire harness and started the return process on the eBay order.

Package in the mail


Getting back to actually working in the car, I was able to get in and unplug the existing harness. I plugged the new one in to the battery computer and the current sensor. The temperature wires just hung there, which would be fine for testing. I covered the power connections, reinstalled the orange battery safety plug, and started the car.

I was able to clear all the error codes on the dashboard through a combination of powering on and off, clearing codes with the ScanGauge, ( and entering a diagnostic mode in the car. What was nice is that this DID prove that the only problem was indeed the chewed-through mice wires!

When I originally posted the wire damage on social media, I got plenty of unwarranted advice, including “why don’t you just splice the wires?”, “you should just use liquid electric tape”, and “you should pop open the connector and just replace the bad wires.”

In this case, all three sets of wires terminate in a single plastic plug that goes into the battery computer. Besides the three wires to the current sensor, there were other wires chewed on as well, although not to the same extreme. I had no idea if those would be an issue or not. And because the wires were all so short, there would be very little to try to crimp or solder to, let alone trying to do that down INSIDE the battery case. There was barely room for one hand, let alone both plus a wire cutter, stripper, and soldering iron.

I’ve also been trying to do things more and more “The Right Way” in my life lately. That means doing anything well, properly, and correct so that I won’t have to do it again.

In this case, it meant removing the battery from the car and completely replacing the wire harness from the battery computer.

I set to work removing all the bolts that held in the battery and pulling away pieces of interior trim and the air vents that cool the battery. Once I finally got the battery out, I set it up on saw horses so that it would be at a nice ergonomic working height.

The end of the battery pack houses the main power contactors, the battery ECU, and the current sensor. I had to remove the current sensor to disconnect the pack negative, and disconnect the two high-voltage cables running from the pack to the safety plug. After that, I could remove the entire sheet metal piece holding all those components onto the pack.

Temperature sensing on the top of the pack is a single sensor, and easily accessible. However, the rest of the temperature probes are UNDER the battery. I had to flip the battery over to get to those.
Once I flipped the pack, I could see that the bottom wasn’t just a simple sheet metal cover. Each cell module of the battery was bolted individually to it! I had to remove all the little bolts to get the bottom cover off. Fortunately, that wasn’t the only thing holding the batteries together, so I didn’t have to worry about compressing them, holding them in place some other way, etc.

With all the cell bolts removed, I could take off the bottom cover.

Cell module temperature sensors


The temperature sensors themselves are very simple and are just connected to the bottom of the cells with plastic clips. I just laid out the new wire harness next to to the old one, unclipped the sensors, and clipped the new ones in the same place. After that, I bolted the bottom cover back on with all those small bolts going into the cells. At this point, I made sure to correctly torque them down. I don’t want the bolts coming loose, but neither do I want them to snap off or damage the cells! I bought myself a torque-wrench just especially for this job ( and tightened all the bolts to 48 inch-lbs.

After that, all the work was just a matter of reversing what I had previously done.
I reinstalled the contactors, current sensor, battery computer, and hooked them all up with the new harness. I got the battery back in the car. Then it was just a jig-saw puzzle of remembering which piece of sheet metal went over which. I reinstalled the air vents to the battery. I reconnected the battery to the main power wires.

After the battery was completely back in, I reinserted the orange safety plug and reinstalled the interior trim and the seats. By this time, it was getting late and it was after sunset. My wrist was hurting pretty bad by then, as I’m still not fully recovered from getting hit by the lumber truck this spring.

Interior reinstalled.


Finally, the car was all back together.
I took it for a test ride by driving to the gas station. The red triangle came on again, but I figured that was just leftover memory. After rebooting, it cleared out again. I also took the car for a long test drive the next day, including going out to the farm store to buy some mouse repellant and traps. Everything was working well.

Two days later, we drove the car hundreds of miles each way to go to a friend’s wedding. No problems whatsoever. (Congrats, Ryland and Kelli!)

Fixing the car was quite a bit of work, but I’m still glad about it for several reasons. For one, I was able to fix it myself. I do take pride in learning new things and am always glad to have a new skill and a little bit of experience from it. Secondly, doing it myself saved me a LOT of money, especially good as my income has taken such a hit in this last 6 months.

Lastly, it was nice making it to the wedding in the car we already own. Our family has two cars, but the other one is a short-range electric car. It’s great for 90% of all our trips, but one of the reasons I chose that car was that we always had the Prius available for road-trips!

Well, we’re back to being a two car family, and as much as I’d love a shiny new Tesla Model 3 or Chevy Bolt, the expense just wouldn’t warrant the upgrade over a Prius and an iMiEV. Times are a changin’, and I look forward to when we eventually replace the “gas-guzzling” 2004 Prius with some form of long-range, quick-charging’, Battery-Electric Vehicle.

Until then, stay charged and mouse-free!

-Ben Nelson

PS: When I asked Ned why he had a spare Prius battery wire harness kicking around, it turned out that he had an entire battery he was experimenting with. The battery was removed from the car, because it was donated to getting punched by giant robots. That’s right, my car now has a part donated from a robot punching bag.

{ 2 comments… read them below or add one }

1 Don October 7, 2018 at 9:55 am


Did you actually get hit BY the truck . . . . or did it turn in front of you and YOU HIT the truck??

2 admin October 7, 2018 at 10:19 am

How technical do you want to get?
Technically, the truck “Failed to yield right-of-way”.
That vehicle turned to a 90 degree angle against incoming traffic, completely blocking all lanes directly in front of me. Police report indicates that I had a total of .75 seconds available to me react AND bring my vehicle to a complete stop to avoid impact.

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