GR Yaris (Gen 2) Auto gearbox specialist / thoughts?

Ecsrobin

Ecsrobin

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So as most will know my engine went bang at around 4-5,000rpm, it also took out my transfer case.

A new engine has been fitted, upgraded and a new transfer case installed. After 31 dyno miles all operating ok the gearbox decided to not play ball and showed an error code P07457F Pressure control solenoid A actuator. Instead of changing one actuator I went for the whole set in a new valve body. Unfortunately that hasn’t solved the issue.

So engine running you can go from park to drive but no gear gets engaged and then when you try and shift it goes to 3rd but again nothing happens. To me that suggests somethings out of alignment rather than a new gearbox but the garage is stumped and so am I.

Online looking at other Toyota DAT transmissions the general thing seems to be check fluid levels and complete a TCM module reset on techstream which have both been done, pre solenoid replacement and after.

Whilst I know I’ll be the first probably with an issue here before I say yes to fitting a new gearbox and still finding a problem I thought I’d throw it to the hive mind for any suggestions or if anyone knows of an auto gearbox specialist they can recommend?
 
You need a diagnose dan type guy who can research the actual condition required for that code to set and follow the data. The factory flow charts are just for your average dude.
It could be a bent pin for the gearbox ecu or a damaged wire but it appears unlikely to be the valve body. The top diag guys in an area are usually well known in the trade, ask around.
 
Being that the code is 'Stuck Off' vs 'Stuck On' the diag is a bit more straight forward. I know you are tuned, have you flashed the vehicle back to stock to see if there was a change? I flashed a few maps on my car and it must have had an issue writing the TCM portion correctly because I had a very similar symptom as you but a different solenoid code, I flashed back to stock, all was good, then flashed the map back on and all was good again after that.

The pertinent solenoid is SL1 and that solenoid runs the C1 clutch that is the main input clutch for gears 1-5. Where you have no engagement that means something is keeping that clutch from applying. I will preface that 'performance' codes like the one your car is setting will almost always end up being a mechanical issue, there are exceptions but those are rare. If this vehicle was at my shop the first step would be to make sure the PCM is commanding SL1 to turn on when put in Drive, it is a linear solenoid and as amperage increase the pressure it sends to the clutch increases. You would need a scope watching the amperage spike in the harness to verify the actual command is being sent. If the amperage does not change when put in Drive they will need to diagnose what is inhibiting the command from happening. The PCM uses the Input and Output speed sensors as a determination as well, you'll want to make sure since you had an engine out that there are no pinched/chafed wires in the harness to the transmission, we see this a lot after engine swaps.

If the amperage does change and the harness is sound going into the transmission then it would be solenoid inspection time. You can bench test all the solenoid by sending power to them to see if they click, if they all click then they are capable of working. You can also check resistance to make sure none of them are electrically failed.

Where they put a valve body on it and there was no change it is pretty safe to rule out a valve body/solenoid issue. I would concentrate on wiring into the transmission. If those are in good order the next step would be to get the transmission out on the bench and see what happened. Any time we have had a Toyota 8 speed on the bench with this particular code it has been a mechanical failure and the C1 clutches were destroyed.
 
sinistriel said:
Being that the code is 'Stuck Off' vs 'Stuck On' the diag is a bit more straight forward. I know you are tuned, have you flashed the vehicle back to stock to see if there was a change? I flashed a few maps on my car and it must have had an issue writing the TCM portion correctly because I had a very similar symptom as you but a different solenoid code, I flashed back to stock, all was good, then flashed the map back on and all was good again after that.

The pertinent solenoid is SL1 and that solenoid runs the C1 clutch that is the main input clutch for gears 1-5. Where you have no engagement that means something is keeping that clutch from applying. I will preface that 'performance' codes like the one your car is setting will almost always end up being a mechanical issue, there are exceptions but those are rare. If this vehicle was at my shop the first step would be to make sure the PCM is commanding SL1 to turn on when put in Drive, it is a linear solenoid and as amperage increase the pressure it sends to the clutch increases. You would need a scope watching the amperage spike in the harness to verify the actual command is being sent. If the amperage does not change when put in Drive they will need to diagnose what is inhibiting the command from happening. The PCM uses the Input and Output speed sensors as a determination as well, you'll want to make sure since you had an engine out that there are no pinched/chafed wires in the harness to the transmission, we see this a lot after engine swaps.

If the amperage does change and the harness is sound going into the transmission then it would be solenoid inspection time. You can bench test all the solenoid by sending power to them to see if they click, if they all click then they are capable of working. You can also check resistance to make sure none of them are electrically failed.

Where they put a valve body on it and there was no change it is pretty safe to rule out a valve body/solenoid issue. I would concentrate on wiring into the transmission. If those are in good order the next step would be to get the transmission out on the bench and see what happened. Any time we have had a Toyota 8 speed on the bench with this particular code it has been a mechanical failure and the C1 clutches were destroyed.
Click to expand...
Thank you. That’s the most convincing answer I’ve had yet. A new gearbox is on order so hopefully that solves the issue. It then leaves me a gearbox to fix or upgrade at some point.
 
Ecsrobin said:
Thank you. That’s the most convincing answer I’ve had yet. A new gearbox is on order so hopefully that solves the issue. It then leaves me a gearbox to fix or upgrade at some point.
Click to expand...
I'd love to get my hands on an extra transmission there are some neat changes made to the base 8 speed that Toyota/Aisin made to get it to where its ate now. I have a company interested in making some kevlar/carbon TCC frictions that I've used in a Mazda transmisison that work great and would increase holding capacity for the converter. There is also the possibility of adding some more clutches in the other clutch sets to increase capacity there as well.

I would also love Ecutek to do something with TCM access but last I inquired they said they had no plans for that.
 
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