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Fingers crossed for you, but I don't understand how hysteresis is being affected this way by the fluid level. Shouldn't the ECU be enforcing hysteresis via its lookup tables? For it to not do so, it would need a failure in solenoid activation, speed sensing, or table lookup. Fluid level shouldn't affect the 1st or last items. Maybe it could confuse a sensor in the transmission making the ECU inappropriately think loads have changed and switch inappropriately to another lookup table?
I'm still stuck on the "happens when I gingerly press the throttle" observation...as opposed to randomly happening whenever. Perhaps that is what you are saying, but you exceeded my cognitive processors.
OK. I'll try to explain. As the car goes faster, the automatic transmission changes gears. It does so at shift points. Those shift points must not trigger on exactly the same state when crossing upwards or downwards in speed. Otherwise, you'd have states in which the transmission would rapidly bump gear up and down if you held a constant speed and load. Hysteresis is a behavior built into the system to make the upward shift trigger be a different condition than the downward trigger. It can be done mechanically, but I think ours is done via the ECU because it's easier to design a system that way. Simpler parts and the ability to adjust shift points by reprogramming the ECU.
So, the ECU needs to know data from the transmission, throttle, and engine to determine what gear it should place the car. Given a set of conditions, it can look up (or calculate) what combination of solenoids it needs to energize to effect a gear setting.
Your moving up in speed crosses through a shift point. As the transmission changes gears, it should put you into a completely load condition. Preferably not one at which you are already at an opposite shift point. If it is immediately at an opposing shift condition, you'd get immediately bounced back down. Normal operation doesn't have this happen because the ECU's typical behavior includes hysteresis. It has to by design, but something is making it not work that way.
Your gradual throttle increase puts the system into more repeatably related states. That is why it is more likely to trigger such a fault. I'm not saying this should be happening. I'm saying that slowly varying throttle rather than rapidly adjust throttle will recreate the trigger for malfunction more readily.
Thanks for the further explanation. I think we are agreeing: mere fluid level should not necessarily affect any of the shift points this drastically, especially if it was "just a little past max". Recall, I first proposed TPS or similar. Perhaps a tranny speed sensor, but I doubt that would manifest when lightly varying the throttle. I think there is redundancy in the speed sensors, so a code would likely result even if just sporadic operation.
But, a TPS (or the device on the pedal side) might be somehow malfunctioning in a way such that a light pedal movement results in an erratic overstated signal being sent to the tranny ECU, somehow mimicking more throttle than actually given. And, since the throttle system is a mechanical to electrical conversion, I usually put my bets on those devices as first failures. But I would also expect the engine throttle to similarly momentarily increase? Unless the blip is long enough to signal a downshift but short enough to not move the throttle?? So the more I think about it, the less convinced I am.
If it were a tranny solenoid, I'd expect a code.
Dang it, Badhobz, what did you do to your car!?!? Perhaps your dealer was right....new transmission!
Another thing that you could check is to use a OBDII monitor and bring up the tach and speedo on your display and drive around. Especially monitor during the times when it is bouncing back and forth on the gears. If the mpg and rpm meters are steady then the problem source is elsewhere but if they are bouncing around, the problem could be with the speed and rpm sensors.
yup... my thoughts too. ill just have to keep driving it for it to pop up again (hasn't done it since yesterday). Pretty sure I just wasted my money on 2 tranny flushes now.
well ive driven it 3 times and it hasn't happened since they lowered the transmission fluid levels. I didn't want to say anything I until I had a few more drives in but I think it might be fixed (trying to not jinx myself).
So i think here's how it might have happened.
first time i went in for a transmission flush was 2017. They must have overfilled it during that time too. Then this strange shifting started to happen roughly a year or two after. I then went in for a transmission flush and they replaced what they took out (still overfilled). Now they finally lowered the levels and it seems to be okay.
do you mind sharing the dealer you used for my future reference? we are both in calif. if you prefer, you can pm me.
also, am i correct that this is your second sc430? i thought you had a silver on black (like mine) but i saw you recently posted a pic of white on saddle. did something go wrong with the silver one?
Im in Vancouver BC Canada. I think I registered before they had Canadian provinces available (I should change that location).
This is my second SC. The original silver one was written off by a careless driver and i started hunting for another one. I love the SC so much i wrote an article about it hahah.
I've never understood some of the hate for the SCs. Fast, comfy, HARD-TOP convertible. Not even the LC500s can say that! For me, though, I had to replace the stock wheels. The only other aesthetic differences are: painted chrome strip on hood, griffin emblem, painted side marker lights, newer LED taillights.
Im in Vancouver BC Canada. I think I registered before they had Canadian provinces available (I should change that location).
This is my second SC. The original silver one was written off by a careless driver and i started hunting for another one. I love the SC so much i wrote an article about it hahah.
thanks for clarifying. before you corrected your location as Vancouver BC, i assumed "ca" meant california. guess that dealership info is a lot less relevant for me now!
sorry to learn of your first sc's demise. here's hoping your second one brings as much reliability and joy as your first.
i read and thoroughly enjoyed your article. it captures everything the sc430 means and is to me.
Originally Posted by degmla
I've never understood some of the hate for the SCs. Fast, comfy, HARD-TOP convertible. Not even the LC500s can say that! For me, though, I had to replace the stock wheels. The only other aesthetic differences are: painted chrome strip on hood, griffin emblem, painted side marker lights, newer LED taillights.
beautiful! i love the subtle mods you've made.
one question: with the newer LED taillights, do you now have upper and lower backup lights?
one question: with the newer LED taillights, do you now have upper and lower backup lights?
Thanks! Your question confuses me, as I don't think SCs ever had upper backup lights? IIRC, those have always been turn signals, with the backup lights always at the bottom of the bumper. The newer taillights are more sleek looking to me. The earlier years had some random circle lenses that I didn't like as much.
Thanks! Your question confuses me, as I don't think SCs ever had upper backup lights? IIRC, those have always been turn signals, with the backup lights always at the bottom of the bumper. The newer taillights are more sleek looking to me. The earlier years had some random circle lenses that I didn't like as much.
sorry for the confusion and thanks for correcting me. my only experience is with my new-to-me 2002 sc430. i assumed the 2006 and newer taillights with the white embedded in the red lens were backup lights.
03-17-21, 08:26 AM
