Hi all again, My car is broken. I think the transaxle plate fell appart inside while on the motorway. Now it won't start at all, it just tries with electric hum and drains the HV battery. Fault codes cleared and nothing new comes up. But the real clue is the clunk and shudder as it tries to start. That bit started today, yesterday it was just locked. Today a clunk and judder. Very weird. What is involed in replacing the transaxle? Or at least to split it from the engine to replace the plate? Can this be done from underneath if I jack it up and drop it down? Or could it still actually be the battery? A P3000-388 came up after the break down (along side the cascade of faults that followed due to the catastrophic fail while giving it beef up a ateep motorway hill at 80mph. I thnk that was due to a little burn hole on a chip in the little BMS, that's replaced now. Not sure what the cause is here. I'm guessing the plate fell apart. Thanks, Deian
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.
What if I said I've been able to turn the engine on the crankshaft pulley. I took the plugs out and I put a socket on an extension bar on the pulley, it turned fine. Certainly didn't feel or hear any metallic bits moving or any abnormal resistance. But trying to start it today, it felt locked and it clunked with a slight forward judder. As if it was very very nearly starting. Part of me wonders if one of the battery cells just pulls the whole pack down so it just can't deliver the amps to start it. I should get a fault code for that. No warning lights, no red triangle. If the motor was off wouldn't that be a more obvious electrical fault? Again what baffles me is the lack of fault codes.
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.
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.
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.
