2006 Prius codes P0420, 0171, 1121, and more rebuilt battery

Hello all,
I am new to the Prius world. I bought an ‘06 Prius (213k miles) from a lady and it had been her first car ever, yes I know, probably a bad idea. I got it really really cheap!! I’ve had it about a month, she’d had it diagnosed at Toyota and they said bad hybrid battery.
So the first thing I did was have it rebuilt by a guy locally who owns a shop almost exclusively for Prius work.
Here are the issues:
When I first got it it would need to be jumped off, replacing hybrid battery seems to have solved that.
Also replaced the 12V battery.

It has never averaged more than 26 mpg on HWY, city, or both.

Codes that have popped up are:
P1121, P0171, P0420, P0A09, and P0A08.
One rare time after I turned it off at the gas station, cranked again and it wouldn’t go into any gear besides neutral it threw code: P0AA6.
I cleared the codes disconnected battery plug waited 10 minutes and it worked fine and 400+ miles later that code still hasn’t returned.

So, the Prius guy told me the bad mpg and the 0171, and 0420 could be o2 sensors and possibly the CAT.

So, maybe y’all can offer some advice.
Since I got the car; terrible terrible gas mileage, and sometimes I have to do the reverse drive then slam in park trick to turn it off, but that’s pretty rare.

Here are the repairs etc I have already completed:
Rebuild hybrid battery
Replace 12V battery
Synthetic oil change
Have run a fuel system emissions cleaner every other tank.
Replaced combination meter because it would randomly not work at all.
Replaced all filters
Replaced o2 sensors
New tires and alignment
New info display screen

And after all of this and through all of this the red triangle of death, the circle with exclamation and parenthesis around it, and the exclamation point in parenthesis they looks like troubled water or dots under it, all of those lights have remained on and consistent.
Even when I use various OBD tools and clear the codes they come back literally immediately...

The new combo meter had 181k miles on it, and the trouble lights are the same as the old one when it was working.

For example today, I took the car on a round trip doctor visit to Baton Rouge so, about 240 miles, and it burned through over 1/2 tank of shell V Power fuel, and the information screen showed the current MPG between 23-26 whether I was holding t 60 mph or doing 80mph.
Now of course when I’m slowing down or not pressing the accelerator it reads 70-99mpg

My battery icon turns green on most trips, never fills all the way to the top, has previously turned blue and a purple ish color briefly before going back white or green.

Basically, what am I missing besides replscing the CAT converter that is causing such terrible MPG?
Also, I’ve read the coolant control valve could be stuck, this may be contributing to the dash lights, but wouldn’t cause poor MPG, and according to real-time diagnostics the engine coolant temp never rises above 190F even while driving 70-80 on the interstate.

I’m not a super mechanic wiz, but if there’s instructions I can follow them, and do a great deal of my own repairs.
I would take the CAT to a shop though.

Any ideas or experience with these issues and how I might resolve the poor MPG? I could honestly care less about the lights being on, but it randomly not wanting to power off, or the one time it would turn on but only go into neutral those things are problematic as is the 19-25MPG out of what is supposed to be a hybrid fuel efficient car despite age and mileage lol.

Thanks for any help!

 

———————

Hey y’all.
Thanks for all of the great tips. I’m going to have to research what to do for each of them because surprisingly enough each of you mentioned things I’ve not yet learned about or heard of.
I used a traditional OBD tool you purchase at autozone or such that my father in law had on hand from last year. It gives very very little
Information... I purchased a Bluetooth OBD tool that connects to my phone and I had to purchase the OBD Fusion App and the specific Prius software through the app. I can program it to give me a very large range of options and values on stats, performance, and I’m sure much much more. It also connects to Auto Doctor, which I thought was a steal for $19.99 for a year subscription.... turns out, the OBD Fusion app and software were the same price and are far more useful...

I thought the one light was tire pressure but didn’t pay any attention to it because just 2 weeks ago I had all four tires replaced and an alignment done at firestone ($430) not too bad considering ... but I guess they didn’t reset the TPMS.

On mention of the brakes, I did read of some Prius’ having a clicking noise when applying the break, I’ve noticed that happening more regularly, and loudly...
I don’t think I have that gun you mentioned, my father in law might, I will definitely ask.

I had firestone check all the fluids, however of course I double checked, and I had already done the synthetic oil change and filter myself so I know it’s current.

If you’ll suggest the possible names of some values to pull from the OBD tool I’ll scan for them and post for your review.

Is it normal, while sitting in park, car cranked, and a/c or defrost turned on, for the car to crank up the regular motor semi loudly every 3-5 minutes and run for about 30-45 seconds and then shut the regular motor off again?


I also forgot to ask in my initial post if the battery and car exclamation point on the info display was directly related to the lights on the dash or if they indicated something different?
Oh yes, A few more items ... I don’t really view them as significant but...
cruise control doesn’t work at all, no indicator light etc.,
And some steering wheel functions: specifically the defrost buttons do not work, so far I think all of the others do though.
And finally, my key fob cranks the car, the key fits the door and unlocks the car... but, the buttons on the key fob and the button on the door will not unlock the car, and I replaced the batteries in the fob, and even attempted reprogramming it but every guide I found was to program a second remote so I didn’t really expect to be successful in that attempt.

attached are screen shots of some of the sensors and values I already have set up in the OBD app. These values are while sitting in park with the car running.

Please feel free to advise as whatever you’ve seen be successful lol.
I too wish I was closer to more Prius gurus

Hey! I guess I must of done something better... I just took the last pic of the info screen and average mpg, and it’s almost up to 28.... LMBO...

Thanks again!
Wayne

 

Oh wow! Thanks... that’s a lot of information and a lot of it got lost on me.. lol...
I’ve posted some of the readings from the OBD reader and the app that I use. In the other comment. I read over those codes and explanations you’ve listed. It makes me rather curious because I’ve definitely got the car to over 80mph regularly, the o2 sensors are new, and I have no idea where that harness is that was mentioned in the DTC Codes you posted.
I’m going to find a mini dvi cable and use that to get the sub codes I suppose. Is there a program needed for it, and hopefully I can use it with a Mac.
Thanks

 

Hi guys, okay,
So I’ve ordered tech stream, we shall see how that goes.

I’ve ready the A08 code could be the inverter or converter or even the pump for it.

I bought the cat converter online for $60 and took to a muffler shop to have it installed, and they ran codes and checked system and said CAT was NOT bad or clogged. Said they would clear codes and I should drive it and return if the codes come back.

So, I took the advice on driving it a distance on as flat of a road as I could get.
I drove it on the interstate at speeds of 75-90mph from Covington, la to Biloxi, ms (approx 100 miles) I filled up at shell with 97 Shell V-Power, and also put in a bottle of Emissions full system high mileage cleaner, the kind that guarantees to pass emissions, I think this is just guaranteed for states like NY and CA and would force it to pass the OBD scan (this was not my goal, I just hoped it would clean some deeper parts and injectors etc)
Anyway, after Biloxi, without refueling I drove to Bogalusa, la from Biloxi, Ms (approx 90 miles) at speeds of 65-80mph. Then back to a Covington from bogalusa (approx 36 miles)
I have been relying on the MFD for MPG data, but this time I refueled and decided to run the calculations myself, and came up with 38.9MPG. Granted, on this trip the MFD, had increased to read (29.1MPG) which is the best it’s ever done.
Before that tank, I would get at most 250-300 miles to a tank.

So now, I’m back to having no clue what is wrong. On this tank I’ve since only driven short distances at speeds under 70, and have 170 miles on this tank and reading about 1 bar over half tank remaining...
So MPG seems to be improving slightly...

I disassembled the MAF Sensor and cleaned it, cleaned the Throttle Body while I was in there.
Still have the A08, A09, and P0171 codes showing and they still come right back on immediately after clearing them.

I have not yet checked the inverter coolant but I will be doing that shortly.

On the MFD screen, I still see the Battery and the Car with the exclamation point, as well as the traditional red triangle of death and the other lights posted before.

One piece of curious info, after I cleared the codes, my Bluetooth OBD reader tells me if the MIL (malfunction indicator lamp) is turned on or off, after I reset the codes it says the lamp is “off” even though it’s clearly on.

Also, on the AUX battery in the back, there is the white plug that we can unplug to disable battery etc, but there is another very small single wire that runs to another much smaller white plug, any idea what this wire is for?

The P0171 code is mainly emissions.... other than replacing the CAT, the Coolant sensor, and the MAF Sensor... I’m not sure what other emissions parts could be fixed...

The trans fluid and other such fluids have not been changed to the best of my knowledge, but surely those would cause other issues like poor transmission shifts, overheating, etc ?
Thanks again!

 

Well Guys... we will find out what comes next here shortly..
I mentioned all of the repairs in previous posts.
As I went to disconnect battery, yet again, for a hopeful fix to a random issue, I noticed this little white lead positive wire was disconnected/unplugged from its connector.
I googled and researched. I found what it was and grabbed some electrical tape, and a little 18 gauge wire, and saudered the new wire to the micro terminal connector, secured it, and reinstalled it.

1st improvement noticed:
when I cranked the car,
The break system light was gone !!

2nd: The cruise control WORKS now!!!

3rd: ran OBD codes, came back with the same DC/Inverter (08 and 09) and Sustem Lean 0171 code... except.....this time when I cleared the codes ... THEY DIDN'T COME BACK!!!!

So I was literally so excited I had to share it before I even got out of the car LOL...
Going to take it for a quick test run and heat it up see if anything comes back... hopefully NONE come back !!!
Thanks for all the advice!

 

Hey again,
So I purchased a new key fob, and you were right the SKS button was OFF. However, I got the new remote programmed and it starts the car, but when I attempt to program for unlocking I get the 2 cycles lock/unlock to indicate the program failed. I’m going to email the seller, I don’t believe it’s a TOYOTA OEM, but it works otherwise, it’s possible it might just be the new fob is faulty, and the fob I have was like you said a used fob programmed like I did before I bought the car.

UPDATE: after the other day of repairing the sense LEAD connector on positive side of AUX battery, I’ve driven the car approximately 175-200 miles with multiple stops, starts, parking, driving hwy and city, and ZERO Issues!!!
The only code that keeps returning is the P0171 and P1121 which I’d assume are related codes.
So, I purchased the new control valve and will attempt installing it later this weekend.
Thanks for any insights!

 

Hey,
Thank you for the information and advice! Yes, that would be correct I did purchase a brand new fob with a blank key inside, but also correct, it is now no longer new since I am programmed it to the car and the seller on Amazon would not except it as a return or even replace it. However, from what it sounds like that would not of solve the issue anyhow. Do you have any idea what the dealership or a locksmith or such would charge me in order to reprogram the remote to lock and unlock the car? Also, to answer your initial question when I purchased the car used, the remote fob that came with it would not unlock or lock the car is by the button on the fob. I have looked into purchasing light stream, and I still think I might; however, what is a seed code? And how do I use it with text stream to reprogram the remote Bob’ I have looked into purchasing LightStream, and I still think I might; however, what is a seed code? And how do I use it with text stream to reprogram the remote fobs?
The only downside to light stream from what I can tail is that a Windows computer is required, I only own Mac computers. So I will need to swing by pawnshop or something and locate an inexpensive windows laptop or netbook in order to utilize light Stream. The only downside to tech stream from what I can tail is that a Windows computer is required, I only own Mac computers. So I will need to swing by a pawnshop or something and locate an inexpensive windows laptop or netbook in order to utilize LightStream.

I will say, though I really do enjoy the Prius and the potential features that it offers, and even the way that it drives and handles, for the age of the vehicle there is so little information how to use, videos, or self-help support available even though they can around four years. There is a great deal of do it yourself and self-help guy made by other individuals, unfortunately, those are not always the most accurate resource. I am actively learning more and more about the car actually only logged on to the forum today to post a question about something else, so I’m glad that I saw your post. Please let me know if you have any idea about the pricing or have any tutorials or two to reprogram myself

 

Update: all right guys, you all have been so very helpful over the past several weeks with my Prius and the issues. However, the error code P0171 will not stay gone for good, or so it seems. This week I finally got the chance to replace the coolant flow control valve, and the engine or radiator coolant. I chose to go ahead and use super long life coolant made for Toyota vehicles. Unlike the tutorial videos, how to guides, and other resources available, when I removed the hoses and the control valve the coolant from the radiator system did drain and I also drink the rest of it in order to replace. However, the coolant from the inverter did not drain, or at least not all of it.

The videos and such resources suggested that the inverter could Coolant would also mostly or completely drained, resulting in meeting to completely replace the inverter coolant. I did lose a little inverter coolant so it seemed by checking the reservoir, so I did go ahead and complete the bleeding process for both the radiator and the inverter after replenishing the coolant in both. And the inverter needed about 1/2 to 1 quart maybe not even that much I did not get to measure it precisely. I did bleed the radiator and the inverter separately with hoses as directed in multiple guides, and the coolant temperature seems to be stable between 180 and 190 varying slightly depending on conditions and speed.
I also purchased the coolant temperature sensor to replace and could not find it on the side of my engine, all of the resources available to show it should be on the top right hand side when looking for a technicality, the driver side of the engine block closest to drive. Since I could not find this, I did not replace the coolant temperature sensor.

Since having completed those tasks, I have driven the Prius approximately 215 miles and have used slightly more than 1/2 tank of gas the MFT says I’m averaging 27.2 miles per gallon, my OBD two reader says that I am averaging between 35 to 30 miles per gallon again, very depending on driving and spe since having completed those tasks, I have driven the Prius approximately 215 miles and have used slightly more than 1/2 tank of gas MFD says I’m averaging 27.2 miles per gallon, my OBD two reader says that I am averaging between 35 to 30 miles per gallon again, very depending on the driving conditions and speed.

So, do I trust the MFD, or the OBDII? Also, there have been a few where the check engine light has come on, the little engine symbol, NOT the red triangle! And I have checked the code and pulled P0171, and twice randomly at different times on different days the P0420 catalyst system throttle position sensor code popped up.

I am now searching as to why these codes are continuing to return. The P0171 (bank 1 too lean) code, and I see on my OBD app the fuel trim averaging .28-.34 them occasionally spiking to .40, I am not sure what to do with this information..

What aspect should I consider replacing or repairing next? I’m still getting pretty rough mpg. MFD says 27.2, OBD app says 35-38.
I know that I’ll be doing a manual calculation when I refuel next.

I’ve included a screen recording of my OBD app displays as well as pics of the MFD and combo meter while driving on the flat interstate with the cruise set at 75mph and AC on recycled at medium speed.

I’ve only ever run shell fuel since I purchased it, and I do a fuel treatment cleaner LUCAS brand, every other fill up.

I just want it normal and to get the fantasy45-50 mpg Prius is known for !!
Thanks again for any advice or tips.

 

Hey there, Thanks for calling that to my attention, and my apologies. Yes, when I purchased the car, the first of the maintenance I completed, was replacing all the spark plugs with the recommended type and the most expensive brand at O'reillys, I know the expensive ones probably work about as well as the cheap ones, but since plugs are replaced so rarely, I thougth it would be a good idea to potentially get a little more life out of them.
Also, in the same day, I replaced the Engine Air filter, Changed the oil to full synthetic (if it wasn't already, didnt have any records) and the filter, I also changed the cabin air filter. I went back to my first few posts, as I thought I'd included those items, but it appears not... lol However, all of this was done at the time of the initial post along with the other items shown. Thanks again!! lol

The MFD is reset every time I refuel, and as shown in the images, the MFD does not seem to be accurate either in the realistic "instant" or in the averaging mpg's.

Prior to replacing the Flow Control Valve this week, about 2-3 weeks ago, I thoroughly cleaned the MAF and the Throttle Body until they were both almost sparkling (With appropraite cleaner).
I have even contemplated replacing the MAF sensor; however, the OBDII app shows the A/F is normal range. So, I am not sure about if the MAF would allow normal ranges if it were not functioning correctly?

As far as inspecting the intake and PCV Hoses, I am not entirely sure how I could do that without removing them all and doing what, the cork in the ends, soapy water (bicycle tire trick)? lol

I read somewhere online that the P0171 code could be a number of things; however, I've slowly checking off the possibility of each them off the list one by one, and honestly seems like I will have rebuilt the entire durn car by the end of it... LOL

I am all game to check the hoses, but I wonder if the hoses were to blame, and intake were an issue if it would not run properly, or even sputter, die, and choke while gs engine was active?
Thanks again, I look forward to trying out all suggestions lol

 

Update again:
Hello everyone,
Alright, so I posted last night while on my way for a short trip, about 120 miles, and when I finished the trip, I had completed 270 miles on that tank of fuel, and refueled at shell, it took 5.424 gallons to fill back up, which according to my calculations is roughly 49.7 MPG. which is AMAZING!! I can totally live with that!! This is what I have been looking forward to!
However, my question is why do these codes keep returning, almost all of the electrical components have been either checked, rebuilt, or replaced.
I don't think I mentioned in my post from earlier today/last night, that I had also replaced most of the mini fuses under the hood, and also replaced the 120A Fuse link in the adapter thing that connects to the AUX Battery.

I really do need to find a thorough detailed walk-through video on where the coolant temperature sensor is located on the GEN 2 prius, I think I may have to dismount the inverter reseroir and some other items just to be able to dig around to find it.

Last night after making my trip, I did some around town driving 10-15 miles total, with multiple stops. It seems that even though I clear the P0171 code, it continuously comes back every time I get back in the car or turn it off and then turn the car back on. After one of my stops, I cranked the car back up and got these codes shortly after cranking, without even moving the car, which seems bizarre. P0171 (too lean), P0A80 (replace hybrid battery), and P3000 (Battery control system). I cleared the codes, and drove around with a few more stops, and none of the battery codes ever returned, just the P0171.
Then occaisionally the P1121 (Throttle/Pedal Position Sensor/Coolant flow control valve position sensor circuit stuck) code has popped up randomly, both before and after the flow control replacement. Is it possible I should look into replacing the Throttle/Pedal position sensor?

I mean if it maintains that kind of actual MPGs, I really don't care what it says... Just curious what is off to continuously throw these codes.

Short 90 Mile trip home to work overnight tonight, I am going to retop off the fuel, and reset trip/MFD/ etc and see how that goes...

Thanks again for any help/advice!!!
Attached are screen shots of the codes.

 

The P0171 does not come back immediately when cleared. It typically comes back on only. When the car has been recently cranked, and sometimes a few miles into a trip it’ll come on. Tonight it didn’t come on when I cranked after it sitting most of the day.

What would you recommend I spray with?