My 05 prius has the P0AA4 and P0AA1 Codes, what can be the problem

<div class='quotetop'>QUOTE(maliy06 @ Feb 26 2007, 04:42 PM) [snapback]396857[/snapback]</div>

According to the service manual, P0AA1 is the #1 main relay and P0AA4 is the #3 main relay. I think it said there were 3 of these relays. In any case, the procedure is to check the relay by checking their resistance with and without power applied across the control terminals. The relays should be open for no 12V and closed (less than an ohm) with 12V. The fix for a bad relay is replace it.

This is the "little bit of knowledge is dangerous". The procedures go on for several pages with lots of warnings because you are in very dangerous territory (High Voltage!!!!!). The codes are set when the hybrid system thinks those relays might be stuck closed, leaving some part of the system energized with high voltage when things should be off. As you are getting codes on only two of three, there may be other consequences and/or causes (would two fail at the same time?).

This is from a very quick read of only part of those sections of the service manual (HV - high voltage and HB - hybrid battery chapters). Just one of these is over 400 pages long.

I'd strongly suggest it is dealer service department time.

- Tom

 

<div class='quotetop'>QUOTE(maliy06 @ Feb 26 2007, 05:23 PM) [snapback]396881[/snapback]</div>

I am not a Prius Tech. But because you have codes on two relays, my guess is that the problem is in the control circuit which could be the computer controlling them or the circuits in between. The codes means that the realys look like they are stuck "on", so "not starting nor clicking in the battery" does sound like some problem other than bad relays since the codes seem to mean that 2 out of 3 relays are always "clicking in the battery".

This may be a case where the 12V battery dying is an effect and not the cause.

As I said before, I don't think this is a home job. Just checking the relays puts you in a potentially life threatening high voltage part of the car.

- Tom

 

<div class='quotetop'>QUOTE(maliy06 @ Feb 26 2007, 05:45 PM) [snapback]396891[/snapback]</div>

Paul,

I took another look at the troubleshooting tree for P0AA1 and P0AA4. There are 3 "main" relays, two on the positive side and one on the negative. The troublshooting boiled down to checking the relays and replacing them if bad. It went like: check #1 - bad=replace#1, good=check#2 - bad=replace#2, good=replace#3. There didn't seem to be any other path unless there are other error codes that you didn't get a report on. If only #3 is "bad" (stuck on), the manual says you have "limited operation", but if #1 or #2 is bad the car is not diveable. I expect #2 backs up #1 (I didn't track down the circuit diagram to be sure), so if #1 won't turn off, #2 is kept off for safety. Hence the not driveable.

I have no idea how you get to this kind of problem from a dead battery, jump start, then stalling. I'd be interested if you report back when the source of the problem is discovered.

- Tom

 

with all the info codes associated with this, plus the sheer danger level of operating on the HV system, highly recommend going to a dealership for this one. good luck.

 

Hello Paul please can you be of help , i am in similar problem please.

 

where are there 2 relay , is it the one with 12v battery or big battery and which side is it ?

 

Please paul where are these relay at the back of the big battery?

 

There inside of the Hybrid Battery case. Have never seen those replays fail. Very rare. There's 3 relays. Two are in parallel and one of those 2 has the resistor in series with the load for soft start to protect the system from inrush.

Much more likely the Hybrid ECU has failed.

In the case of the OP the car probably threw alot more dtc's that would have pin pointed it closer. Having Hybrid issues after a 12 volt battery jump is highly suspect of a reverse polarity jump. Check all the fuses especially the dome and the 2 mounted on top of the 12 volt batter post assy.

 

I have similar codes now after a good used pack put in. Get the P0AA4 code and nearly every light on the odometer display lit up. Tried four cheap code readers and not sure the one that actually sees some codes is reading or resetting all of them. Question is.. is the #3 relay (by code) and "negative HV battery relay really stuck closed (connected)" by code listing legit... despite it reading open or 3meg ohms? Or do I just need a better code reader than this $60 harbor freight unit to reset the code properly.. unplugging the 12v battery for a day doesn't seem to do it..

I think that tech was right.. there's water or moisture inside the relay, I think its safe for this computer tech of 30 years to remove that battery power side side also and open them up or replace.. Some signs of water. the accident removed the people from the roof. so. it has a little rust on two bolts.. but not much. This is socal but we did have some rain this year 2018.. Pack vottalge very good for sitting two months. 7.55-7.57v on all cells but the bookends as usual(?). those were 7.50v. I'm ready to bail on this whole car. Anyone want it? It's been maintained well. LOL.

 

Update: Realized the pack went in yesterday so I hadn’t tried the overnight reset of codes via 12v disconnect.

Now the Centec brand code reader shows an ! Sign because it knows something is wrong, but there are no trouble codes now. Which means my old battery pack probably have the bad relay.

Also I’m hundred percent sure at least once I forgot to put the orange plug in and tried to start the car during these exploratory tests of readers and voltages on modules. I believe I only need a better code reader and maybe a new battery.

 

Update: indeed it was the ubiquitous need for a better code reader which can really reset prius codes. Because the newer ones couldn’t be found outside of China, I got the older mini VCI cable which claims it only works with the older operating system such as Vista ( which is what I installed). And I finally got around to fixing an old but still very useful laptop sitting in a drawer just in case I ever needed to run a windows app like this. (Note: this is the third windows app I’ve had to run in 25 years for a total of about three actual boots. And one of those is for data recovery the other, an inane security camera configuration).

I reset the codes and found out the new battery assembly case around and beneath The orange HV disconnect plug was not just bent in the front and side directions.. but also it was bent up when I compared it to the old one by 2-4mm only!

After trying gentler methods for a few minutes, a couple of short but firm taps for the hammer did the job. And I made a mental note of the dangers of doing that and determined that it was fine. Sure enough one more reset with the high-end software and the car was running like a charm.

My choice of Repair I believe is far superior to replacing individual cells. Instead of doing that for $300 I found a battery pack which came out of a car crash so badly from front and rear that the occupant had to be removed from the roof via the jaws of life hydraulic system. I’m happy to report that the battery will was not affected by this accident in the slightest. But getting a complete battery packAfter testing it first, is better because each one of those cells grew up together and has experience the same where in tear and age. It also saves a lot of labor hours taking apart the entire battery pack. The key was to find somebody with a newer battery pack and half the mileage at 100 K miles in my case, who did not require a court exchange. This means the phone and $50 I paid for this battery pack delivered, will be completely erased when I sell all the 24 remaining good sales for roughly $700, not to mention the relays in the EC you for the battery pack etc. etc. the thought of reconditioning the sales over a week. Did not appeal to me either, but maybe I wimped out.

I believe my gas mileage has gone up by 20% or more. The only regret I have is that I forgot to use the red spray paint type battery terminal protector coating onto all day 28×2 battery terminals, most likely using a poster board cut out some type. To ensure these coding would only go where I wanted it to. There’s no way I’m putting Vaseline or any other liquid-ish under heat coating onto those terminals.

 

So they orange grip was not seating correctly?

 

I had to P0AA1 code. I figured it out. I believe it will be the same for the P0AA4 code. Hit me up if interested. It was NOT the black relays.

 

Can you help me

 

Please share your solution. I have the following codes: P0A94, POAA4, POAOD, POAA1

 

The P0A0D is reporting something very simple: the safety interlock circuit that protects you from the high voltage systems is open.

Very often, that is because the orange service plug back at the battery has been removed at some point, and was put back but never fully seated so as to complete the interlock circuit again.

So that would be one easy thing to fix, and then see which other codes come back.

If you search for the codes and spell them correctly—P0A94, P0AA4, P0A0D, P0AA1, there is never a letter O in a trouble code—you will often get more and/or better search results than you will if you spell them with letter O.