P0A4B Code, Transaxle/Generator

Run, don't walk to Steve Woodruff at Plug In Hybrid Electric Vehicle PHEV and he will fix your Prius using a salvaged transaxel for a more reasonable price. His garage is in Scottsburg, Indiana.

JeffD

 

If the transaxle is busted on , definitely go with salvage transaxle. And you have Steve Woodruff to help you being in Indiana.
I recently hit a big rock which cracked the transaxle housing and also bent suspension cross member.

Incidentally my 2005 also had 165K when it happened. I got it fixed with salvage parts from my regular mechanic who had not previously worked on Prius. Finding a good salvage transmission was what took most time. I was in same boat as you contemplating whether to put in so much money.

Now 800 Miles and 2650 $ later I am more than happy. I am getting 54 MPG while I never got more than 52 MPG previously.

 

DTC P0A4B means that the generator resolver in MG1 is not working correctly. This helps the hybrid vehicle ECU keep track of the MG1 rotor position. The wiring harness, the transaxle and the hybrid vehicle ECU are the suspect components.

It is interesting to see that the problem is intermittent. If the car has previously been in a front-end accident or flood, perhaps the wiring harness might be causing the problem. Good luck.

 

Another possibility I would check: make sure the generator position sensor plug on the transaxle, and the wires to it, are clean, properly seated and making contact.

 

If it were me, I would slow down, take a deep breath and drive it until the code(s)/lights come back. Although you do have the stored code, it is very difficult to troubleshoot when the problem is intermittent (and not currently evident). Replacing the whole transaxle may be too big of a jump (at least it would be for me at this point). Look at Patricks comments for advice ("The wiring harness, the transaxle and the hybrid vehicle ECU are the suspect components"). If you replace the transaxle and it turns out to be the Hybrid ECU, you're going to be mad at yourself.

There is a possibility (remote as it may be) that this problem will not resurface (then you will be happy you waited). My experience with the Prius so far has been, lights/DTC's appear, I get really freaked out and assume the worst, next thing you know, I restart the car and the car's running fine for months. Now, this may not be your experience but you won't know if you don't give it some time.

I suggest having a plan in case it happens again (tell a friend/family member/work you may need help if your car dies). Of course this is a dicey situation that may leave you stranded.

If you don't want to deal with that, I strongly second jdenenburg's advice to contact Steve at Autobeyours. He is a straight shooter who is extremely well respected. He is also a Prius expert with all the parts you could ever want for a Gen II. Hopefully you are close to Scottsburg and not near Gary/Chicago.

 

Yes he's right on....I would check that first thing. Its out in the open and the plug assy gets rusted and the connectors inside rot out. Its the electrical plug right above the 2 small coolant hoses that enter the trans. It has a bolt that holds the sensor in.

Which is why I spray lube all connectors. keeps the water out and the connector assy will not rust.

 

If the generator is "locked up" then the gas engine won't start. I suspect a connector problem too. Or it could be that the trans is in fact on its way out. But you can get a good used one put in for $1500-$2000 if it turns out to be that case.

 

Mr Blue,
How have things been going since this experience? I would really like to know because I had the same experience last Friday afternoon...

I was about 40 miles into a 175 mile trip. Just before hitting the road I filled up with gas at a new gas station. My Prius had one square left when I filled up but it wasn't flashing yet. It is a 2004 with 78,000 miles on it.
About 40 miles on the road the engine went dead and 4 warning lights came on. I went for about another mile on just the battery but it was draining fast without the engine so I pulled over and the car became unresponsive and wouldn't even turn off anymore.
I called AAA and they towed me to the dealer.

I thought the problem was bad gasoline.
I got the dealer to tell me the code and they said it was the P0A4B. They said I need a new transaxle and computer for the generator and it would cost $5,800.
I found this forum and this thread by googling P0A4B and so I contacted Steve in Scottsburg, IN. He was really helpful and had a transaxle he could sell me and after speaking to him we realized it would be better to send my car to him and let him diagnose and repair because he said it is unusual for my Prius to need a transaxle with only 78,000 miles.

I started trying to figure out how to ship my car to him and asked him what else I should check before I ship it. He said check the Mass Air Flow Sensor to be sure if it was bad gasoline or not.
I went to the dealer and told them to check it but they were not cooperative and it's like they were code Nazi's. They kept saying it is code P0A4B, we cannot check the air flow sensor. I finally got them to agree to check it however during this conversation I learned from them that my Prius was running.

Since it was now running I asked them to let me give it a test drive. They didn't want to let me do it but finally I got them to and I rode with one of their mechanics.
The car ran fine, the engine was running fine, and the battery was charging like it should when the car runs. There didn't seem to be a problem with the Mass Air Flow Sensor because it was running and didn't shut off. It is not leaking anything as far as I can tell.

So I have decided to take usnavystgc's advice and drive it as is and hope there is not another problem. I called Steve Woodruff through the whole process and he was extremely helpful and told me he thought my decision was a good solution.
I upgraded my AAA so I get the 200 mile tow if it breaks down again and if that happens I will be sending it to Steve. I also bought a code reader so I can find out what is going on before taking my car to the dealer or anyone else.

The thing is I'm a sales rep and making 200 mile trips one way every week and 200 miles back home but I will take my chances.

Does anyone have any idea what this glitch is?...

 

This has to be a loose connection in the wiring harness or elsewhere. That's the only way it could trigger the fault code then upon reset, not come back and be fine. I would highly recommend cleaning the contacts on the plug that Edthefox5 spoke of.

 

I went and got my car from the dealer last night. I had to pay $221 for having them look at it.

So far I have driven about 20 miles and thought I was in the clear but today the red triangle and check engine warning lights came on.

I used my code reader and it was the P0a4b again. However this time the engine continues to run with the warning lights on. I was less than a mile from home and drove back and luckily still have the car I borrowed from a friend.


I had popped the hood earlier today to try & find the plug Edthefox mentioned but I'm not sure which it is. Is it the one above the dipstick and a little to the right? Just below the air filter?

Also if any of you would be willing to post a list of all the connections I should check I would really appreciate it. I am going to read through the thread again and list all the wiring connections that have already been mentioned and check them this weekend.

The thing is the dealer was supposed to have done this, oh well.

I am about to go to autozone and buy the lube or whatever it is I need to put on all the connections.

 

It's been almost a year since my posts on this problem and I have not had any issues... until last night...

I got in my car to go to my Friday night job and as soon as I power on it lights up like a christmas tree with warning lights, even the red triangle.

I had to get to work so I decided to take my chances and drive it with all the warning lights. It was going fine until about a mile down the road I noticed I was down to only one bar on the battery. I turned off the power at the red light and let sit for a few minutes then when the light turned green I turned it back on.

Fortunately the engine was running and it started to charge the battery back up.

Today I got out my code reader to find out what the warning is and of course, it is my old friend P0A4B. I drove across town this afternoon about 20 miles and no problem. After using my code reader the warning lights went off.

Here's my ideas as to why this warning popped back up:
-cold weather, it's been around 27 degrees here, maybe it is triggered by the cold, last time it happened was in the cold
-it's related to a long trip, last time I had driven >150 miles, this time I had just gotten back from a 200 mile trip earlier in the day
-the computer gets cold
-the transaxle freezes in place
-on my long trip I ran the vent heater without the AC on, could this affect it?
-when I turn off my car after driving around town there is about a 10 second buzzing noise, I guess a powering down noise, could it be related?

I just wanted to report this update in case anyone else has the problem. Maybe those who have already posted or newer Prius owners...
I am going to continue driving since that's what I did last time and had no problems.

Any ideas or recommendations?

 

Not so lucky today. All the warning lights came back on but the engine ceased and did not kick back on to charge the battery.
I went as far as I could then had to coast into a parking lot when the battery drained. Oddly enough when the battery drained the car became unresponsive. It wouldn't even power off.

I checked the codes and this time there were two codes: P0A4B AND P0A4B Pd. I'm not sure what the Pd means it was off to the side on the code reader and the p was sort of on top of the d.

I had it towed to the dealer and am awaiting diagnosis tomorrow.

 

Just got off the phone with the dealer. They said it is not showing any codes at all. They said the 12 volt battery is not holding a charge and recommended we start with a new 12 volt battery. I think he said it would be $296. He said if the battery will not hold a charge it can kick off some of the codes and effect the engine engaging.

I told him to let me know what else it needs for the 100k service and let me know. I will most likely have them go ahead and do the 100k service and a new 12 volt battery.

Since no one is responding to this thread I take it the P0A4B code is a fluke and just a glitch in my particular Prius and the one other individual who originally posted.

All I can figure is the cold weather causes the 12 volt battery to malfunction because as I said this happened last year in the cold yet I drove it for 11 months after the last incident and another 25,ooo miles.

If anyone gets the P0A4B code, I hope you find this thread instead of having a dealer sucker you into paying $6,000 for a new transaxle.

 

I think you should authorize the 12V battery replacement, but hold off on the 100K mile service for now (which will cost $500 or more). See if P0A4B comes back.

If it does, then you know you'll need to replace the transaxle and in that case you might decide to get rid of the car. Should you make that choice, then there would have been no point in performing the 100K mile service.

 

Good point, I went ahead with this course of action. It's gonna cost me $324 just for the 12 volt battery job. I guess I could've saved some money if I had my personal mechanic do it but it's there at the dealer and I don't know for sure if I could get it to my mechanic without towing it.

I am hoping this is all it needs. I will be monitoring and will report back anything that comes up...

 

Yes, that is around $200 for the battery and the rest for labor.

 

After taking a closer look at some other threads, I am learning some details about the 12 volt battery. I am guessing the dealer will use a Toyota battery.
Should I check with the dealer to make sure it is charged and if it is a certain type of battery?

 

It is likely that the dealer will use the Toyota TrueStart battery which actually is produced by GS Yuasa, the original equipment manufacturer. You might want to confirm this since you are paying top dollar and don't want some bargain brand substituted.