Hello, I have a 2010 Toyota Estima Hybrid E-Four X. The car runs perfectly fine when I'm driving around the city. But as soon as I go on the motorway and drive above 50–60 mph, it starts showing fault codes and stops accelerating. I have to pull over, turn the car off, and restart it. When it starts again, the fault codes are still there. After driving for a bit at around 30–40 mph, the same issue happens again. Eventually, the car won’t start at all unless I disconnect and reconnect the battery.

I had the car checked and two fault codes came up:

• P0A94 – DC/DC Converter Performance (active)
  
• P0A80 – Replace Hybrid Battery Pack (pending)
  

Some garages have suggested replacing the DC/DC converter, but the person I bought the car from said he already replaced it and it didn’t solve the problem. I’m not sure if that’s true or not.

Another garage told me the battery might be the issue and that a weak battery could be causing the DC converter to fail. I also came across a forum post where someone with the same model had a similar issue, and replacing the transaxle fixed it for them.

I’m really confused now. I don’t want to replace the converter and still have the same problem, or replace the battery and find out it wasn’t that either. Can anyone please give me some advice on what I should replace first? Thank you. Also, has anyone experienced the same problem? And is there any mechanic near Birmingham or the West Midlands who was able to fix it?

 

P0A80 is 100,000% a bad hybrid battery. I have NEVER seen an instance where a P0A80 occurred when it wasn't the hybrid battery in HUNDREDS of instances. ZERO.

The ONLY time you see a fake P0A80 is if there are issues with the 12V system, i.e., the 12V is so low, it causes multiple errors across all computers. When this happens, it looks like every single system in the car is failing because you have over a dozen codes.

P0A94 is almost always an inverter replacement. The DC-DC converter is often in the inverter, but that varies, and I know absolutely nothing about the Estima as that is not available in the U.S or on the Toyota Techinfo website.

Depending on model, there are ±24 different variations on the P0A94 code based on the detail code read by Techstream or a professional grade diagnostic tool. You can't properly diagnose a P0A94 without professional tools. While most are coded "DC/DC converter", it often has nothing to do with the DC/DC converter.

Lastly, in many instances of the P0A94 code, Toyota indicates:

If any other codes besides P0A94 are output, perform troubleshooting for those DTCs first.

That means you should ignore the P0A94 and resolve the P0A80. Once the P0A80 is resolved, if the P0A94 is still present, THEN you resolve it.

You need to replace the hybrid battery with a KNOWN GOOD hybrid battery.

 

Thanks for getting back to me. I’ve been to over 10 mechanics and they all said the DC converter needed replacing, so I got it changed today for £600. I drove less than 20 miles and the same problems came back. The warning lights showed up again saying "Check Hybrid System," "VSC System Check," and "4WD System Check."

Now the mechanic says it might be the hybrid battery. I’m really confused about what to do next. I read on a forum that someone with a similar issue had to replace the transaxle, but I don’t know how to figure out if that’s the problem in my case and how to know for certain the problem is caused by the transmission.

All the mechanics relied on the diagnostic tool, which pointed to the DC converter, so I feel like I wasted £600. Maybe I should have trusted the previous owner, who said he had replaced the DC converter twice before and the problem didn't go away.

 

Did you actually read my response? I have already given you a complete answer to your situation. You have provided nothing new to the conversation.

I have included my post here again in case you missed it:

"West Midlands/Birmingham" implies that you are in the UK, so I don't think this is a language barrier. Your English isn't THAT different from the colonies.

If I am somehow being unclear, please ask appropriate questions. If I'm just not giving you the answer you want to hear, that's a "you problem."

 

I read your reply and even said thanks. I didn’t mean to offend you or make you that upset lol. It just feels like you’re a bit mad. I was only trying to help others by saying the DC converter wasn’t the issue in my case.

Today, I replaced the hybrid battery with a known good one for £1,000. After driving 20 to 30 miles, the same issues came back. The same two fault codes showed up on the OBD scanner, even with different mechanics. I saw the whole battery pack get replaced myself, and I bought a new DC converter, so I know everything was done top notch.

What do you think I should try now? Replace the transmission?

 

I'm not mad. I just prefer not to waste my time. Your response indicated you had taken the exact opposite to what I (and Toyota) recommended, i.e., pursue the P0A80 first and then the P0A94. Again, I am going off data for similar models as Toyota US does not have information for the Estima though wiki says it is similar to the RX400h drivetrain. P0A94/P0A80 criteria are nearly identical across multiple Toyota hybrid models.

Unlikely you got a "known good" battery for £1,000. If you have a P0A80, you have a bad battery. I've never personally seen it in several hundred events, but the battery computer can also be bad, but when most batteries are swapped, the entire assembly, including the battery computer are swapped. That may or may not be the case with the Estima.

The only other option here is if there are other codes that aren't being pulled (P0AFC for the battery computer), and if all of these professionals are indeed professionals, then they should be using professional grade diagnostic tools that can read all codes and freeze frame data. P0A94 should be presented as P0A94-XXX where XXX is a three digit detail code to help pinpoint the issue. If you are only getting "P0A94," your are dealing with amateurs/hacks that haven't invested in the proper tools.

Lastly, a professional shop should be able to connect to the car and observe the "known good" battery block voltages. How do those look?