How to choose a good used transaxle. Ideas?

[orange4boy]

I'm about to start to repairs on an 03 Prius that is throwing P3120.

ADDED: This transaxle died because a leak in the sump ran it dry. Not a reliability issue.

How can I be as sure as I can that I'm getting a good used transaxle?

What I know so far:

1) High pot test the windings. Can I do this with the 3 main leads:

Anyway, we checked between each of the 6 cables with the transaxle case with the megger and found that all 3 MG2 cables had continuity to ground, meaning there is a short to ground in one of the windings. All 3 of the MG1 cables had the proper resistance, specified in the manual. This was the same on both transaxles we diagnosed; only MG2 was bad.

I will bring a Megger to the wrecking yard with me for sure.

2) The oil can be visually inspected and smelled for burning/colour. It could be sent out for testing but this takes too much time.

Are there any other ways to check it.
Are wrecking yards mileage ratings trustable?

Thanks for your input. I may opt for an MG2 replacement from Art's but I have to weigh the pros and cons.

[bwilson4web]

Try this with your transmission first:

1. Make sure rear wheels have chocks - you don't want it to slip or move in the next test.
2. Shift into "N" - this releases the parking pawl
3. Make sure opposite wheel is chocked
4. Jack up one wheel - you want to spin it by hand
5. Spin wheel and try to detect a 'pulsing' resistance - this is the signature of shorted MG2

The windings are 3 phase with all tied to a common point inside the transmission. The short should be across one winding. Rotating the wheel using two DVMs across two windings should show a measurable voltage drop at any given speed. Be sure and compare all three sets of windings. Same test works for MG1 although we've not seen an MG1 fault.

Bob Wilson

[tochatihu]

If you remove the transaxle pan, it will have some amount of metal bits in it. The ferrous ones will try to stick to the magnet. Hard to say what an acceptable amount would be but less is certainly better. If you can look into the pan of your '3120 trans' you will have at least one point of comparison.

If the seller of the used transaxle will offer a written warranty that would be best. Short of that I have no idea how much to trust them.

Here is a list of the subcodes from P3120 from the Graham Davies miniscanner manual:

P3120 - HV Transaxle Malfunction

234

Energy Balance Malfunction. Small reduction of motor magnetism

235

Energy Balance Malfunction. Large reduction of motor magnetism

236

Energy Balance Malfunction. Small reduction of generator magnetism

237

Energy Balance Malfunction. Large reduction of generator magnetism

239

HV Transaxle Malfunction. Shaft damaged

240

HV Transaxle Malfunction. Generator locked

241

HV Transaxle Malfunction. Torque limiter sliding

242

HV Transaxle Malfunction. Planetary gear locked

243

Motor Resolver Malfunction. Motor resolver inter-phase short

244

Motor Resolver Malfunction. Motor resolver inter-phase short (When there is a
history that the state of malfunction continued during inverter fail safe mode)

245

Motor Resolver Malfunction. Open or short in motor resolver circuit

246

Motor Resolver Malfunction. Open or short in motor resolver circuit (When there is a history that the state of malfunction continued during inverter fail safe mode)

247

Motor Temperature Sensor Malfunction. GND short in motor temperature sensor

248

Motor Temperature Sensor Malfunction. Motor temperature sensor malfunction

249 Motor Temperature Sensor Malfunction. Open or +B short in motor temperature

sensor

250

Motor Temperature Sensor Malfunction. Motor temperature sensor performance
problem

253

Generator Resolver Malfunction. Generator resolver inter-phase short

254

Generator Resolver Malfunction. Generator resolver inter-phase short (When there is a history that the state of malfunction continued during inverter fail safe mode)

255

Generator Resolver Malfunction. Open or short in generator resolver circuit

256

Generator Resolver Malfunction. Open or short in generator resolver circuit (When there is a history that the state of malfunction continued during inverter fail safe mode)

257

Generator Temperature Sensor Malfunction. GND short in generator temperature
sensor

258

Generator Temperature Sensor Malfunction. Generator temperature sensor
malfunction

259

Generator Temperature Sensor Malfunction. Open or +B short in generator
temperature sensor

260

Generator Temperature Sensor Malfunction. Generator temperature sensor

performance problem

[orange4boy]

Try this with your transmission first:

1. Make sure rear wheels have chocks - you don't want it to slip or move in the next test.
2. Shift into "N" - this releases the parking pawl
3. Make sure opposite wheel is chocked
4. Jack up one wheel - you want to spin it by hand
5. Spin wheel and try to detect a 'pulsing' resistance - this is the signature of shorted MG2

Will do, when I get it home. I'm not optimistic but would be thrilled if it's a simple problem

Here is a list of the subcodes from P3120 from the Graham Davies miniscanner manual:

I will need a scanner to get the codes. Is there a good miniscanner that will work with the Prius or should I invest in a used graham. Will a scangauge work?

[Patrick Wong]

I'm not sure why there's interest in the subcodes. All of them point to a transaxle problem. If you want to retrieve the subcode you have to use the Toyota diagnostic laptop or hand held tester. Although the Ecrostech (Graham Davies) miniscanner documentation lists the subcodes, that device is not capable of retrieving them.

Unless you have the ability to obtain individual components and rebuild the transaxle, who cares exactly what is the failed component within the transaxle?

Regarding the original question, I suppose you would want a transaxle from a low mileage vehicle, but this assumes you can trust the claims made by the seller.

[bwilson4web]

Originally Posted by orange4boy

. . .
I will need a scanner to get the codes. Is there a good miniscanner that will work with the Prius or should I invest in a used graham. Will a scangauge work?

Sad to say, there aren't many good solutions:

• Graham miniscanner - no longer in production and as Patrick pointed out, it does not report subcodes. However, the Toyota scanner does.
• 3d party scanners - Hobbit has been working with independent mechanic groups and tends to follow the technology closely. I would recommend a PM to him on the state of the art. A local Huntsville Prius rebuilder showed me a laptop with software that appeared to cover a lot more details than the Graham scanner (I'll send him a PM and ask.)
• Toyota scanners - the gold standard ... try to find one!

The reason for listing the subcodes is the ambiguity group resolves to the transaxle or in some cases, wiring. It is unlikely to have a wiring problem (although there have been reports of rodent wiring damage) but when diagnosing a problem, an open mind driven by symptoms is critical.

IF you should run the car by the Toyota Service Center for a diagnostic readout, make sure the service writer understands you want not only the codes but the subcodes too. For good measure, ask them to read out the traction battery module voltages (might as well get that out of the way early.)

Bob Wilson

[tochatihu]

OP was considering MG2 vs. full transaxle replacement. Presuming the subcodes are known, some of them would indicate at MG2 replacement is insufficient.

May have mentioned this before - as you are in Vancouver BC, can you find the shop(s) where all those Prius taxis go? Somebody there must have a reasonable level of experience with these vehicles.

[orange4boy]

Unfortunately, due to the logistics, I don't think I will have time to stop at the dealer on the way home.

May have mentioned this before - as you are in Vancouver BC, can you find the shop(s) where all those Prius taxis go? Somebody there must have a reasonable level of experience with these vehicles.

I will have to research that too. I'm hoping to avoid dealing with any shops though. I would like to get some kind of scanner though. Will hopefully find one that works with Toyota sub codes. (does not seem likely)

I have a friend who was a mechanic who might help me do the MG2 swap if I decide to go that route.

[bwilson4web]

From good Prius friend, Hobbit:

I think AutoEnginuity has reasonable coverage for the Classic,
as well as the second-gen. I haven't asked them about the
third-gen yet but I suspect that's going to take them a looong
time to get going.

He has looked at many of them and I trust his judgment.

Bob Wilson

[orange4boy]

Excellent. Looked it up. will get one for sure. I could even use my palm smart phone. A small price to pay to keep away from the Dealership pirates.