How to choose a good used transaxle. Ideas?

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

 

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

 

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.

 

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

 

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.

 

From good Prius friend, Hobbit:

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

Bob Wilson

 

If you have a ground fault in a winding, that's *not* going to
show up as rotor cogging when you turn it. That would be
symptomatic of a winding shorted to itself or another one, much
more rare as a problem. You will get megger continuity from all
three leads of a given motor to the case in the event of a ground
fault because they're all Y-connected inside so it's essentially
one big hunk of wiring in terms of what the megger sees!
.
Note that several of the codes have to do with rotor demagnetization.
That's always a mild risk for a motor if the windings are ever
subjected to excess currents that build very strong opposing
fields, but I don't think anyone's actually ever turned up a Prius
that had that sort of problem. Those rare-earth PMs are pretty
stable, and I sort of wonder how they get those suckers magnetized
in the first place... probably some games with heating.
.
_H*

 

The journey begins!

I'm not sure what 'cogging' means ... engine runs but runs rough? Or is there a 'pulsing' when the car moves or is pushed about?

Hard to push in "neutral" means the transaxle has failed ... unless you find the drive shafts and CVTs connecting to the front wheels have a serious problem (very unlikely!) When in "neutral," all power to the transaxle MG1 and MG2 is cut.

To have mechanical resistance pushing the car, there has to be a shorted, loop in MG2 and possibly MG1. Disconnecting the inverter MG1 and MG2 and still having a mechanical resistance turning one or both wheels and you know it is the transaxle.

SAFETY: the traction battery has an orange, safety interlock accessible from the trunk. Please pull that before dealing with any of the power electronics.

Yes as would the inductance.

Bob Wilson

 

Cogging in an electric motor is the interaction of the magnets
with the reluctance of the stator poles as you turn it. You've
probably felt it if you've ever played around with a stepper motor.
Which is effectively what the MGs in the Prius are -- big-nice person,
computer-controlled steppers with three phases instead of two
or four.
.
_H*

 

That is failed! The short is not a 'designed' loop but involves some carbonized insulation.

None. But it makes sense to disconnect the inverter and verify the 'cogging' remains. It would be a shame to swap a transaxle only to discover a short, intermittent or otherwise, in the inverter.

Hummm, very, very improbable.

The built-in display has no units. Let's worry the traction battery after getting the transaxle working.

Bob Wilson

 

Please scan my battery experiment page and let's chat some more. The NiMH batteries are very good but they are not bullet proof. Go carefully into that area!

Bob Wilson