2002 Prius lacking power with high revs of engine after a few minutes o driving but restart fixes it

Hi all,

I am new to this forum and need some help with my 2002 prius. It runs well and everything works with 1 weak cell in the HV battery p3006 and 03017 so I isolated it to cell #13 reading 6.6v. I am going to replace the weak cell next week and I will be careful not to touch the 2 ends of the battery and electrocute myself. I will also clean all of the connecting strips and place the cells in descending order (volts).

After I drive it for a few minutes, the car loses power and the engine RPM becomes high. Sometimes the LCD screen would flicker. The strangest thing is that everything resets and if I pull over and shut off the car/restart, the car runs great.

Has anyone encountered this problem and if so, what is the fix? Thanks in advance.

 

Thanks for the input. Since I already bought a used (tested good) cell, I am going to install it to see how it works out. I bought the car recently and want to put some miles on it to make sure everything else works before I sink money in the future to upgrade the HV battery to Gen II cells or buy a parts car for it. I will update the thread with results.

BTW I read that it was a good idea to buy a good transaxle so I picked one up taken out of a wrecked car for $300.

 

I received the used cell from Ebay for $40 and took the HV battery out. I was doubtful that one single bad cell could cause all these problems. I took the battery out and put it back all together without any mishaps.

After taking the bad cell out, I understood why the car ran so badly. The side of the cell looked like it suffered from a mini explosion followed by a small fire as there are black carbon burn marks with a piece of solder inside of the cell exposed and visible from the outside. It partially melted the side of the adjacent cell. After I replaced that single cell, all of the warning lights went off and car runs great getting 45+mpg.

Amazing how one single cell can make the car almost undrivable.

 

Here is a picture of the failed cell. After driving for a couple days, the P3006 code comes up again with a p3076 for abnormal air flow by battery cooling fan so I think I may have to take the battery completely apart and match the cells. In the meanwhile, the car runs fine with 400+ miles driven at 44.2mpg. Notice the crack on the top of the cell on the left and right corners.

 

Update after replacing another cell that tested unusually low but it was tricky to track down because it tested the same voltage with the rest right after a drive but voltage drops much faster than the rest of the cells overnight. This time I took every one of the cells out and tested them with a voltmeter to arrange them in descending order. It was difficult because I drove the car shortly before the battery removal and the cells were measuring around 8 volts and dropping over time. The reading would change and I had to rearrange the batteries because some would drop a little faster than others so that presented a little bit of difficulty. In the end, the highest cell had 7.99 volts and the lowest had 7.81 and 7.80 with most of them around 7.91 and 7.92. In the pack, there were 11 gen 2 cells and 27 gen 1 cells with the weakest 2 (7.82 and 7.80 volts) from the gen 1 so I will replace them next with gen 2 cells.

One word of caution is during the reassembly of the cells, I had both hands on the metal 3/8" socket extension turning the 8mm nuts tying the cell terminals together and felt a small electrical shock. I was wearing shoes on carpet and did not touch anything with both hands other than the extension to turn the one single nut so I did not short myself on anything. I am still puzzled as to how electricity flowed through my hands. Needless to say, I used thick rubber gloves for the rest of the nuts.

A few hundred miles later, no more check engine light and the gas mileage went up to to around 47mpg+ as opposed to 44mpg before. The car runs in electric mode only much longer than before especially in traffic. A couple bad or low cells so far seem to make a big difference.

 

The bus bar had to be bent a little and it was not much of a problem as I took a flat head screwdriver and tapped the bus bar (only 2 had to be done) to make the "step".

As to the shock, the only think I can think of is that I had grease on one hand but not the other because I sanded all of the bus bars and greased them with normal grease to reduce future corrosion. I tied in all of the bus bars on one side and was half way through the other side before I felt this shock though it was more of a buzz feeling and relatively mild.

A code 3006 kicked in for a little while during one of my drives but the car was going through what seems to be a re-balancing of cells. It went into limp mode for 10 minutes and afterwards it went away.

 

An update after more than a year.

I have replaced all the modules in the 2002 prius with gen 2. and working well.

I also bought another 2002 prius with a bad battery pack. I bought a 3rd Prius (parts car) 2002 that was rolled over and took the 3 year old (Toyota dealer replacement battery) out to fix the 2nd Prius.

It seems the gen 1 battery pack in the second car has different characteristics compared to the first Prius with the gen 2 modules. The gen 1 battery seems to run longer on battery and I have to step on the accelerator more before the ICE turns on.

Another unrelated topic. I used a load tester for a 12v battery and tested the individual modules. It is not a very precise measurement but it will give you a good comparison of the strengths in different modules in the pack.

 

The first gen 1 Prius I bought already had 18 gen 2 modules in the battery pack. The gen 1 modules were going out one at a time every few months so I replaced them one at a time with gen 2 modules. I had to take the battery pack apart 5 or 6 times to replace individual gen 1 modules that went bad. Eventually, I found a wrecked gen 2 Prius at pick your parts with an entire battery pack so I changed the rest and had a few leftovers. After the gen 2 module replacement, I had no more failures. This was a cheaper way to keep the car on the road and also I like trying different ways to make something work when possible. If anything blew up, I figure I could figure out how to fix it especially with all the expertise here.

There is a moral to the story. If you don't want to take apart your battery pack several times, it is better to rebuild the whole pack with gen 2 modules especially if you have to pay for labor.

After having to take apart the battery pack many times, I now unscrew all of the nuts on one side and remove the entire strip on one side first. This makes the entire battery pack into 38 7.2V modules that are not connected in any kind of series and renders it harmless.

I did have to bend one copper strip connector as the gen 2 modules were a little bigger than the gen 1. Every time I had to replace a module, I simply will move the bent connector as I have all gen 2 on one side and gen 1 on the other side.

I figured out a while back what was causing the 3006 cooling fan problem. When I bought the car, the battery pack did not have a top cover so the cooling fan for the battery pack had no effect. I eventually got a top cover and all is working well.

I took that Prius off road for more than 30 minutes at Mammoth mountains and later at other places when I went camping and shooting at BLM lands. It is the only Prius I have seen taken off road. I did bang the oil pan a few times on rocks but nothing more than some scrapes. The car has about 35k miles more on it than when I made my first post. In many ways, I like my gen 1 more than my gen 2. With the 3 year old gen 1 modules, the car got 51.7 mpg average for the last tank of 352 miles. My gen 2 gets me around 46 driven in a similar manner.