Replacing Transaxle

Before doing large-scale work that requires a lot of time and money, it is first worth diagnosing the hybrid installation and finding out the reason why the engine does not start.

There should be errors and reading error codes is the primary goal.

P3000-288 The power management control ECU alerts the driver and performs fail-safe control based on error signals received from the battery smart unit. This DTC is set when the SOC (state of charge) of the HV battery starts to drop as a result of leaving the shift lever in N, running out of fuel, or a malfunction in the hybrid control system.

 

There's no inspection plate or nothing I don't think like that like a regular automatic has I don't believe so your choices will be to pull the transaxle so the drive axles have to come out of the transmission usually I undo the lower ball joint at the bolts on the control arm so I can pull the axles out and leave them hanging. And then the inverter has to come out and so on and so forth and the transmission usually comes out the top I guess you could take out the wiper tray and drop the whole crossmember engine and everything but then it's got to go back up.

 

I don't remember checking this on my gen 3, but some gens do have a small handhole in the blanking plate that comes down from the flywheel-end of the engine and closes the lower portion of the bell housing. There is a rectangular plastic plug that closes the handhole, and you can pop that out and feel around through it a little.

Sometimes when the coil springs in the input shaft damper have been beaten to smithereens, you can feel fragments of them if you feel downward in the bell housing.

But you described an electric hum and the engine not starting. You can get a first idea what's going on by standing at the right side of the car and watching the crankshaft harmonic damper (the thing that would be the crankshaft pulley if the engine had a belt).

If your buddy pushes the power button and you hear the spinning of MG1 in the transmission and the engine crankshaft stays motionless, then you will certainly need the transaxle off to see what is broken; likely the input shaft.

 

I would do what chap is talking about and see if in fact the crankshaft pulley turns not that you can turn it with your hand with a socket on a pull bar of course you can I hope you can your engine's free good to go now you want to see if the motor that's supposed to turn the engine is actually turning the engine not you turning it but that motor If so then we're looking elsewhere I got a funny feeling you're not turning the engine with the electric motor and that's something physically broke that doesn't really get a code like if you throw a rod you might not get a code maybe for misfires or something but generally for a mechanical failure there's usually not a code broken rod things like that

 

I'm willing to bet there's nothing wrong with your transaxle because that problem has never been presented on here since Gen1 Prius... If there was a problem it would be in your dampener like Chapman explained and that would be due to ignoring a rough running engine from a failed headgasket for way too long. And the fact your engine is trying to start indicates that motor generator in the transaxle is fine. Most common problem with your symptoms in Gen3 is a failed headgasket. I've also heard lots of noise and no start from a Gen3 engine due to a failed vacume hose.

 

If the symptom is MG1 spins and the engine doesn't, I would expect that it is past time to be worried about the damper, because the damper's life becomes very easy and peaceful again once the input shaft breaks off.

 

What's the miles?

 

With a broken shaft, I wonder if you could even hear the motor generator spinning? It wouldn't be very loud? And there would certainly be way more error codes than a P3000. Regardless, OP's symptoms are not a broken shaft because they said: "...The real clue is the clunk and shudder as it tries to start."

 

What's inevitable from trying to start it too many times is the high voltage battery getting drained down and getting the error code for Hybrid battery voltage being too low. But if all you got is a P3000, that's usually a hybrid battery that's been sitting for a long time and needs a charge and balance, or has a failing cell, or has corrosion in the Voltage Sensor harness where it plugs into the ECU,

 

The clanking may come from the damper when the springs break.

ENGINE ASSEMBLY COMPONENTS by MAX2 posted Mar 3, 2025 at 9:51 AM

But your high-voltage battery is discharged and until you charge it and find out the reason for the failure to start, you should not disassemble the engine and gearbox with MG1.

 

They usually break in conjunction with coolant in cylinder, a “something had to give” scenario.

 

It's a pretty big motor. Kind of a zoomy sound. One of the people it's happened to posted a recording. (Don't know how long I'd need to search that link back up.)

When the input shaft breaks, it does not also vanish. There's still a broken stub of an input shaft stuck in the splines of the damper, and the broken end of it may still be pretty close to the stub that's still sticking out of the tranny. The actual sound you hear when the stub sticking out of the tranny starts to spin could depend on individual circumstances.

Even with broken springs the damper will transmit rotation from the input shaft to the engine. It'll just clank over until the spring stops are touching and then the engine turns.

If, on the other hand, you hear rotation from MG1 and that rotation isn't making it to the engine crankshaft at all, the damper and springs are probably not the main concern anymore.

 

Yea... All that makes sense, but in any of the above scenarios you outlined you'd have alot more than a P3000 for error codes. And that brings us back to the contradiction that OP has a P3000 but no warning lights and red triangle. That makes no sense!

If I had to place a bet I'd put it on way more error codes exist and for some reason OP isn't seeing them.

 

Waitin' on the miles.

 

There are a couple ways the OP could supply more information that would help.

One would be to look for a better scan tool and post whether there are more codes (or even just INF codes for the P3000).

Another would be to watch the crankshaft harmonic balancer during a cranking attempt and see if it turns.

(That is, if a zoomy sound is heard from MG1. If there is not even a zoomy sound, the car may be declining to crank at all because not enough traction battery charge. That'd be a P3000-388 if I'm not mistaken.

 

Might well find "bits" in there. I've never popped ours off either, but I believe that's what it's there for.

With the engine off, if you rotate the engine (socket on the crankshaft at passenger wheel well), would the damper rotate as well? Or the park pawl prevents this, for starters.

 

I think those blanking plates are pretty standard parts, probably shared with other cars.

On a conventional automushic transmission, the torque converter might be bolted to the 'flywheel' (usually a much lighter/thinner version, since the attached torque converter can supply some of the mass) with bolts through from that side, and you might use that access hole to undo those bolts one by one as you turn the crankshaft around to present them.