Lowest mile Gen 2 Prius. 5,156 miles. Back on the road after sitting 12 years.

A couple days later I got back to the shop and the goal was to assess whether it was roadworthy enough to bring it to my home.

I put it up on the lift at the shop. Didn't find any more chewed harnesses, no fluid leaks, or any showstoppers. That said the tires certainly were a little bit questionable, being pretty dry rotted from sitting.

Scanned the car and found the check engine light was on because of a problem with the driver front wheel speed sensor. I inspected that while I was underneath the car and didn't find any obvious debris or blockage, nor any chewed wires. That would have to be added to the list of things to track down.

The one thing there was a lot of was spiders and spider webs. A little freaky but I didn't want to mess with it too much because I didn't want them getting all over the shop.

There was little rust on it for a Wisconsin car, even though it sat so long outside on a concrete parking pad, The underside looked great as far as I was concerned.

I checked the hybrid battery again just to make sure it really was healthy. Everything looked good so I wrapped up and hopped in for the 26 mile drive home.

Again, it was a nerve-wracking drive, but at least I felt a little more confident than the initial drive.

Given all the dirt, grime and mouse debris, I wore my mask on the way home. (So don't judge if you ever see someone driving in a car with a mask on! They have a reason!)

I made the mistake of turning on the climate control. Oh boy! Chewed up pieces of car insulation, napkins, dust, mouse droppings, etc flew everywhere. Gross! I immediately turned it off and added that to the list of tasks!

The multifunction touch screen was non-responsive. Added that to the list of tasks to investigate.

Got a nice massage while driving because the tires definitely had flat spots from sitting so long.

Arrived home at 5,155 miles and 51 mpg

 

Nice, but gross. That's a fair assessment when I got home. Because the car had such low miles, much of it on the surface might appear nice. But as soon as you look below the surface, or open the doors and inhaled, it was gross. Really gross. If you've ever come across mouse nests you know what the smell is.

In these pictures you'll see the mouse nest, and all the black dots are mouse poop.

I took a bunch of initial pictures of the interesting little features that were still present, like the airbag warning tag, and the written instructions below the CD changer slot.

The prior owner also included some bags of items from Toyota including oil filters, license plate frame, and other goodies.

The car had factory cloth floor mats as well as rubber mats for the front driver and passenger footwells.

As previously mentioned, the exterior was covered with plenty of dirt, grunge, and lichen. I couldn't really tell the condition of the paint other than the clear coat was peeling off the rear spoiler.

The biggest challenge for this day was when I removed the glove compartment and found the extreme mouse nest jammed in there. I had an initial clean out of it, but I knew I would need to visit this over and over again.

An interesting side note I forgot to mention. In the morning before picking up this car I happened to meet up with a friend of mine who used to work at the local Toyota dealership. He was helping me with a key for my Nissan Leaf.

I mentioned to him about this car, because I knew it was serviced at his dealership. Before I even got too many details out, he immediately knew the owner and the car. You certainly remember a unique low mile car like this, especially one that got a $10,000 add-on PHEV system. You see, my friend was one of the very few authorized installers in the country that could install Hymotion systems at a dealership.

Anyway, he told me a funny story about how one day this car came in for service and when he accessed the rear hatch of the car he noted there was about 300 lb of pennies in the back!? He had to move them around in order to get at the place where he was working on the car. Good thing the springs had been upgraded when the PHEV system was installed!

I only found a couple of pennies when I did my cleaning, but I did find an empty coin roll paper sleeve for quarters. Fun.

 

Since the car ran and drove, next up was checking out the status of the Hymotion PHEV system. I knew I would have to remove it to properly clean the car. I was also pretty sure I didn't want to leave it in there since it's kind of a unique thing that takes up a lot of space.

Having worked on hybrid cars and EVs for over 20 years I know quite a bit about these systems and have come across them many times. Usually it was to decommission them and remove the system and the wiring harnesses from the customer's car. A rather involved job.

I figured if the system worked it could be installed into some other enthusiast's car, or if it didn't work it could be dismantled and used as parts for other projects.

I initially had bypassed the system, because I didn't know whether or not it was safe. I removed the bypass plug and hooked everything back up properly. And started at my assessment.

Made sure there wasn't any high voltage leak to ground nor any obvious external damage to any of the high voltage wires. I also pressed the inertia reset button. This is a resettable switch that denergizes the system should it ever be involved in some sort of impact. Once that checked out I started up the car and turned the system on.

The Hymotion system has its own self-diagnostics and reports out any errors via a blinking red LED on the dash.

I have the installation manual as well as the owner's manual for these systems. And a good chart of what each of the blink codes means.

Turns out it was flashing six blinks.
Consulting the chart, it indicated a problem with the battery sub module temperature sensor. So that meant opening up this high voltage pack for closer inspection.

Once I opened it up, I could clearly see that mice had been inside here as well! I started inspecting the wiring of each sub module and sure enough found one with broken and chewed temperature sensor wires.

Fortunately, being the nerd I am, I have some old Hymotion modules with the temperature sensors are still attached. I opened up a spare module, set it near the damaged one, and plugged in the spare module's temp sensor into the main system.

I went to the front of the car, turned on the Hymotion system and everything came to life! No more blinking error codes from the Hymotion system.

From there I charged up the Hymotion system via the bumper plug. And later drove the car in EV mode with the Hymotion system contributing to the propulsion.

Amazing.

A car that sat 12 years, unused and the hybrid battery came back to life, and so did the Hymotion PHEV system. I wouldn't have imagined it was possible.

 

Now that I knew the Hymotion system was working, I took a quick side quest to swap out the Multi-Function Display (MFD) since the touch screen wasn't responding.

Fortunately from working on hybrids for many years I had a spare MFD sitting around. So I took out the front vents and upper trim work and quickly had the replacement swapped in and working.

I still had all the rear trim work removed but it was piled up on top of the Hymotion system and main battery in the hatch area. But I would deal with that another day.

 

Then the day came to remove the main Hymotion system itself. The batteries and electronics unit. I would leave the actual wiring harness in for a little bit longer since that is a job in itself which involves a lot of reconnecting spliced wires, clipping off where it's tied into other harnesses, etc.

The system itself weighs about 200 lb. So I was not looking forward to lifting it, but I knew it had to get out of there so I could clean underneath it.

Again all I can say is, "gross". The rear interior panels that surrounded it had their insulation chewed up and turned into mouse nests. And then the back was used as public restroom for many generations of mice.

I used my pet odor spray to spray those panels let them soak while I went back inside to eat my Wheaties so that I could lift out the system.

Removing the system itself was rather uneventful, I managed to get it out myself and set it on an old desk I use as a mobile workbench at times. And then I transferred it to the best rolling cart I had around; an old family kids wagon. That's where it still sits today.

So if anyone's interested in getting an A123 Hymotion L5 5Wh PHEV system installed in their Gen 2 Prius, give me a call or a private message and we can work something out.

I sprayed down the other parts of the panels in the rear and let that soak.

Meanwhile I'd noticed the exterior lichen had caught the attention of folks who walk down my alley. It was hard for them to not pick at the car as they walked by. So I left a nice sign that said Biohazard Do Not Touch on the car. I figured that might deter the casual passerby.

 

I took the Prius to a local shop to get new tires put on. Hankook Kinergy ST. They are a low rolling resistant tire that I've been happy with on other cars of mine in the past.

This trip added an additional 1 mile to the odometer: 5,156 miles total for those keeping track at home.

Next up was finding the cause of the front driver side wheel speed sensor error.

Jacked up the car and took off the wheel. Unbolted the sensor from the knuckle to make sure there wasn't any debris, a cracked sensor, or a damaged ring on the hub. Nope. All that look good.

So I started following the sensor wire up into the area behind the plastic wheel well cover.

Ugh. More evidence of mice. The fabric insulation on the backside of the cover was all chewed up and a bit of a nest created. And a little more visual inspection found where the mice had chewed the wires.

The wire damage wasn't on the sensor side of the harness, it was actually on the car side of the harness. So that meant I'd have to call around to some colleagues to find a parts car I could clip a pigtail off of and splice in. Which I did the next day.

This repair isn't one for using cheap butt splice connectors. The specific ones I use for this cost about $2 apiece and have integrated shrink tubing on them. Especially important in this high moisture area.

 

The same day I repaired the speed sensor wires I had another go at the climate control circulation fan behind glove box. Remember the big mouse nest I pulled out from there?

Well guess what? There was even more!

Rather than trying to just clean it through the little slot where the cabin filter slides in, I decided to remove the fan housing in its entirety. This made the cleanup much easier.

After I got it reinstalled, I turned on the fan. I was glad I had my mask on, because once again, chewed up bits of insulation, napkins, etc came blowing out the vents.

I spent some time turning on and off the system while switching between different vent settings to try to get the debris out of the vents. Once in a while debris would get caught in the vent grates and I'd use a pick and a vacuum to suck the debris loose from where it was lodged. Good times!

Finally the debris diminished to a small amount, but I guess over time there still could be pieces that work loose every so often.

 

Next up was to completely empty out the rear of the car from the base of the rear seats all the way back. This means the hybrid battery, the back seats, every single bracket including the one underneath the 12 volt, all the venting, all the trim, and the battery fan.

This is because each of these items in one way or another were touched by mice and needed to be cleaned up and disinfected.

I wasn't worried about refurbishing or deodorizing them at this time. I just needed them out.

Once everything was out, it took most of the day too spray things down and wipe things out. Mask on, gloves on, lots of spray and paper towels.

When the hybrid battery was removed, since I already knew the electronics were damaged I didn't clean that at all. But I did take a quick look at the battery posts, buss bars, and voltage sensing wiring. I thought it marginal at best, so I set the pack aside and put in an order for new OEM wire frames, new OEM buss bars, new OEM nuts, and new OEM voltage sensing wires.

 

Next it was time to tackle the Hymotion system's wiring and decouple it from the stock wiring.

I went back and looked at my notes from long ago from working on these systems. It had been a few years since I'd had to decommission one. But once I started on it, the memories came back and it was out within a few hours.

It ties into different places like the computer behind the glove box where it ties into the EV mode white wire. Then behind the power button. Underneath the driver side dash. It continues along the entire driver side of the car underneath plastic trim.

It ties into the high voltage battery leads as well as the rear tail lights, and the 12 volt battery pack.

The trickiest places are by the high voltage computer itself, but it's doable.

In some places the Hymotion harness is simply tapped onto wires and it can simply be clipped off. And other places where wires have been cut and then routed through the main Hymotion harness and back to its regular route. So those needed to be restored. Of course after all this it needs to be wrapped in protective sleeves or electrical tape.

The Hymotion dash button needs to be removed and unplugged. Added a note to myself too find a dash blank to cover the spot where the switch used to be.

Under the dash and at the computer behind the glove box those wires simply needed to be capped.

On all good days work getting the wiring back to stock.

This should make it so that any future techs that work on the car won't be so confused by all the extra Hymotion wires.

 

On October 29th I borrowed an ozone generating machine. I piled the interior trim, metal brackets, etc into the car and I gave it two 15 minute sessions of ozone, with 6-hour breaks in between.

The next morning I moved everything back out so I could work on refurbishing the brackets.

As part of the process I also started working on the battery pack, removing the damaged electronics end and replacing it with a spare one I had here.

In the process, I noticed that the temperature sensor wiring harness for the battery was chewed off and damaged. So I dug up one of those out of my spare parts as well.

Removed the battery modules from the bottom of the case so that I could clean out everything and replace the temperature sensors. Also put on the new buss bars, wire frames, nuts, and voltage sensing wires. Also replaced the main negative lead and the safety cutoff holder with used ones that were in much better condition.

As I was reassembling things, I realized I didn't order enough nuts for the battery module posts. So I placed the order and put on some used nuts temporarily so I could start and move the car.

The brackets themselves were cleaned off with a wire wheel and then spray painted with some rustoleum primer.

I've attached a photo of how bad the electronics end of the battery pack was. Also a screenshot of the battery data from the Dr. Prius app.

 

I started November with opening back up the hybrid battery again, and swapping out the remaining used nuts on the battery module posts with the additional new ones I previously had forgotten to order.

Putting the lid on the hybrid battery I moved back up front to replace the upper glove box lid. I noticed that it had a typical problem where the housing for the hinge cracks, which makes it so that the lid won't open all the way. In addition, the spring starts to slightly raise the dash pad cover. As usual, I had a spare one of those sitting around for just such an occasion.

After this, I moved on to doing some more documentation of the condition of the engine compartment, interior and exterior. I contacred a detailer to help with additional cleaning tasks and I wanted them to fully understand what they were getting into.

I did a bunch of additional disassembly under the hood like removing headlights and removing the cowl tray because I wanted to make sure the areas underneath them got cleaned, as well as provide more access to the engine itself for cleanup.

I apologize if some of these pictures are duplicates from other individual posts.

A couple other fun things.
I snapped a picture of the oil change sticker inside the car that matched the online Toyota service records for this car.

I also grabbed a big chunk of moss that was growing in the windshield wiper area and saved it for later to grow in with some other house plants or something just for fun.

 

November 3rd was the first day that the detailer was coming to begin the exterior cleaning.

I quickly removed the gasket that was still attached to the rear bumper from where the Hymotion system outlet had been affixed

I took some last-minute pics of the original patina of the car.

The cleaning was a slow go. Lots of soaking to let the water and soap saturate the dirt, grime, and lichen.

It was a good first attempt at cleaning with promising, but not complete results.

 

The detailer came back for a second day and took another shot at the exterior and cleaned more of the interior panels. I had them taken out of the car. In the end I'm not sure if that made things easier or harder.

I took some pics late in the day after he was gone but things were not fully assembled yet.

In the evening, I decided to do some more of the work myself on the headlight assemblies and the engine compartment. As well as the hybrid battery fan.

Late that night I used the dealership's online booking feature to schedule a 7:30 am appointment the next day for its first oil change since awakening from its 12 year slumber.

I quickly reassembled the rear interior, etc. and went to bed.

 

Friday, November 7th, 2025 is when the car returned to the dealership of its origin for its first oil change in 12 years.

I left my house at 5,156 miles.

This car was sold to the original owner from the very same dealership on August 26th, 2006. First oil change at that same dealership was February 23rd, 2007 at 201 miles.

It had 13 oil changes since then, the previous one on October 18th, 2013 at 4,889 miles.

This would be its 14th oil change at 5,180 miles, 191 miles and 12 years since the last oil change.

As part of the service the dealership did an inspection and found a few thingsthat needed attention. Lke the fact that I hadn't replaced the cabin air filter or rear windshield wiper yet. The biggest item of note were that the shocks could need some servicing. So I added that to the list of things to attend to.

As part of the service, the dealership provided a complimentary Carfax which fully documented this vehicle.

The recommended 5W30 oil was put in and the total cost of service was $88.88.

I drove home and arrived with 5,206 miles on the odometer and got 52.2 mpg for the 50 mile round trip.

I knew it would take a day or so for the service to be reflected in the online Toyota service record. So I waited patiently.

 

When I got home from the oil change I did some more inspection under the hood. It was amazing to see how clean it was around the oil cap compared to all the other cars I've ever owned.

That said, I found that there were still mouse debris remnants that seemed to be magically appearing on top of the engine coverings. Mainly seeds and sunflower hulls.

I did some investigation and found that there was actually a mouse nest made of insulation inbetween the two layers of metal in the hood. So I started digging that out.

I also found lots of debris underneath the foam insulation that is attached to the hood. Geez! When will it end?

 

The next day the oil change was reflected in the online Toyota service record so I grabbed a screenshot. So interesting to see.

There's still one major area of the car that we had left uncleaned which was the rear hatch surround.

It was a grungy mess. It also had the typical small separation/gap between the upper and lower panels in the top corners of the opening. This would allow water to get in the car.

I decided it would much easier to just remove the entire lift gate than to work around it for cleaning and sealing.

With the help of an assistant we removed the lift gate and set it aside.

I spent the day cleaning the opening and finally getting to the point where I could give it a final wipe down with degreaser in order to prep it for sealant.

The 3M degreaser is something I was introduced to at one of my first jobs. We used it for prepping metal to be painted. It's the smell of my youth. It's quite expensive but does a great job.

By this time we started to have snow flurries. Since the liftgate was off the car, it left the rear exposed to the elements, so I moved the car into the garage.

I happened to have some roof sealant handy that could be used at low temperatures, so I decided to give it a try. I generally use small spatulas, wooden stir sticks, or a thin flat blade screwdriver in order to spread the sealant around. It wasn't pretty, but I was able to fully seal the leak-prone seams.

Fortunately, this isn't really an area you notice once the lift gate is reattached. But I won't get to that for a little while.

It's too cold outside for the next few days so I'll finish cleaning the liftgate itself later in the week.