ECU / Red Light Issues. No Start. - New Prius Owner

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Did you pay the dealer for this repair estimate, if so they should've supplied you with the retrieved OBD2 codes (DTCs) on the paperwork.

Many find using a toyota hybrid compatible OBD2 scanner as helpful when diagnosing a problem, as it may help save time and money.

Have you already checked the 12v battery for voltage, and again the 12v voltage at the jump points under the hood (driver side), and also be sure to check the battery cables attaching to the 12v battery and to the body (negative ground strap).

Please post the DTCs (OBD2 codes) here and we can offer additional guidance.

 

how many miles on her?

 

I got a new (used) prius a couple weeks ago. Apparently sold by a weasle. It's never started reliably, and the red triangle light comes on / off.

You came to the right place.

Jumping it would start it though. I replaced the low voltage battery. It started 4 more times, then won't start at all. Not even with a jump.

Explain what you mean by 'it started 4 more times'. Does this mean you successfully drove the car 4 seperate times? or that you heard the engine spin for several seconds and then turn off, 4 sererate times?


Also, the red triangle + CEL, and several other dash lights stayed on now.

I'm curious if the battery depleted itself trying to start the engine....... but there are many possibilities. We need actual codes, which will most likely only be able to be read by a prius/hybrid aware code reader


The toyota dealer gave me a very vague diagnosis.

No surprise, but if you paid a diagnosis fee, they owe you the code printout.

I'd really like to get some feedback before I spend $2500. Honestly, after like 2 hours on the web, I can't even figure out what the parts are that they need replacing.

Again, you came to the right place. If needed, I have every computer you may need.
The important first step is the codes.

Is there any chance at all that you connected the 'jump' backwards, even for a second? If so, this almost always blows the large fusible link in the underhood fuse box, plus a couple or three fuses. The fusible link that blows is under the clear plastic cover, directly below the underhood jump point as seen below.

 

Most here will use a mini-vci cable with Techstream (same software the dealer uses) on a windows device (or emulated).

If you would rather try using an OBD2 adapter, then read up on some of the options here : Hybrid battery diagnostic and repair tool for Toyota and Lexus - Once you have an OBD2 adapter, then try one of the apps like : Dr Prius/Dr Hybrid, Hybrid Assistant. I've successfully used some cheapo OBD2 bluetooth adapters ($2 shipped) before, but wouldn't recommend it.

Hopefully the dealer will come clean with the DTCs that you've paid for. Is the vehicle is still parked at the dealers?

 

The P0AC0 is: Hybrid Battery pack current sensor circuit range/performance and trouble areas are:

1. HV battery assembly wire harness or connector
2. Battery current sensor
3. Battery ECU

The P0AFA is Hybrid Battery System voltage low and trouble areas are:

1. Junction block assembly (a busbar module on the battery)
2. Number 2 wire frame (a wire harness used in the HV battery to sense module voltages)
3. Battery ECU

Most likely the P3000 is just the hybrid system letting you know that the battery ecu is throwing out a fault signal.

The P0420 is catalytic converter efficiency below threshold.

Personally, if it were my car, my suspicions fall completely on the HV battery and its ecu. Something is going on with it. A good visual inspection by a knowledgeable person would probably resolve it. That's no surprise, whether it's original or a typical rebuilt replacement. I'd have to tell the dealer no thanks for now. If it's original, it's probably due for replacement. If it's a typical rebuild, you'd be better off replacing it anyway.

As for the TSB: It's kind of strange to me that the TSB is dated May 28th 2009. Would make sense to me that a 2009 Prius (yours is 2009 right?) would have this 'improved' ecu and hardware. I would be VERY surprised if a 2009 didn't have the 47092 battery ecu. The other one, you could probably get from ebay for a hundred bucks if desired. I was wrong, they're all over ebay for 40 bucks.

TOYOTA: SOME VEHICLES MAY EXHIBIT A M.I.L. ON CONDITION WITH ONE OF MORE OF THE FOLLOWING DIAGNOSTIC TROUBLE CODES (DTCS): P0AC0; P0A1F; P0A7F; P0AFA (HYBRID BATTERY PACK/SYSTEM). IMPROVEMENTS HAVE BEEN MADE TO THE HV ECU AND BATTERY ECU HARDWARE TO CORRECT THESE CONDITIONS. *PE

 

The HV battery ecu commonly gets corrosion on the pins where the #2 wire frame plugs into it. So this wouldn't be a surprise to me. I have seen it be bad enough that a pin or two breaks off on the ecu side. This ecu is relatively easy to replace and requires no programming at all. Just a chop and swap/plug n play or whatever you want to call it.

The HV Control ecu is located behind the glovebox and on the far passenger side. I've never swapped one on an operable car, but have removed them from salvage cars. A bit more of a PITA. It is also my understanding that the HV Control ecu needs to be programmed with the cars VIN, and a previously used ecu CAN be rewritten with a new VIN

 

You may want to check the dealer reported "vehicle mileage", TSB/recalls, and maintenance/service history at https://toyota.com/owners

Check for mini-vci cables on Ebay (unless you only support Bezos), then try sorting by US sellers, as one might be available more locally.

If you have the time and tools, use this guide to get you towards the HV battery and related ECU : 2004 – 2009 Toyota Prius Plug-and-Play Car Harness Installation Instructions | Hybrid Automotive

Optional: You can also inspect and clean the HV battery fan while working through the process (step #23).

Once you have all of the trim and stuff out of the way and the HV battery exposed (and after taking all safety precautions in step #6 and #13, and any others you may need), take a look at the HV battery ECU and connector by remove the hybrid battery junction cover (step #14), neither one should NOT look like this : 2005 179km Wont go to Ready Mode | PriusChat

Or look like anything that might be fired and pictured in this thread (a gen1 thread FYI) : https://priuschat.com/threads/the-battery-fires-at-ecu-sense-connector-thread.151412

If bored, open up the HV battery cover, and look at the corrosion around the bus bars and wires, and then create a game plan from there.

There are a bunch of threads here that can help identify where the leaks are, and how to seal them. Here is one to get you started.

 

Never seen toast that looked like that. I think you meant it's, figuratively, toast and then you could leave the word figuratively out, as we all know that's what you mean. Even if you meant it is burnt like toast, the word is still figuratively. (Sorry, been inside a while now, I couldn't help myself.)

All joking aside, most likely the actual ECU is ok, but no guarantees. You would need to replace the plug on the harness, the connector on the board and two (or maybe 4) of the pins within the plug (the remainder can be moved over from the old connector), which I'm not sure whether that is easier said than done, in terms of actually getting those parts. You could look through the EWD (electrical wiring diagram) (more info) to find the plug, connector, and wire pins.

A less elegant, but easier, way would be to buy a new Wire Frame No 2 from Toyota and a second-hand ECU off eBay/Amazon or an auto wrecker yard/pick-n-pull.

I hope that helps and good luck.

 

The new harness should be all you need for the front side and the wiring. On the rear side, you just clean up the connecting plates and terminal nuts and reuse them.

 

You should have cleared the codes after your work, they won't necessarily reset by themselves. You are at a loss as you obviously cannot read all codes wit your std reader, so you are not going to know what it is worried about and means you cannot make a judgment call as to whether the codes are something new to worry about or just residual from before your work. If the triangle is still on, you can use your reader to clear all codes and see if any come back. If they don't then you could assume that they are from before your work. If they do not clear or come back after, then you will need to get your Techstream running so you can read them with the knowledge you are starting with a clean slate.