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99' GS400 Transmission Issues.

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Hey everyone,

I have a 1999 GS400 with, (and I know it's a lot), 350,000ish miles. Shes pretty old, but the engine runs great and there are no issues on that part. However, my check engine light has been on for a pretty long time now and my OBD reader throws a "shift solenoid c electrical failure" code. My transmission shifts extremely hard, and I do not believe it shifts passed 3rd, but I am not 100% sure on that part yet since there is no clear way of me telling. It takes a few seconds when I put my foot down for it to downshift. The fluid is in moderate condition, no sign of transmission wear at all.

But this is where it gets weird.

This has happened I would say maybe 3 times now, but the check engine light will go away and the transmission will go back to normal.

Also, i should note, when the CEL is on, the digital shifting w/ the steering wheel buttons does not work; however, when the CEL is off, it does.

The few times that the CEL went away, it was relatively warm outside, and it lasted about 15 minutes each time. Then out of nowhere, I would hear a thunk, and the CEL comes right back on. The last time the CEL turned off was about a month ago, and it has been on ever since then.

I have read up on a few forums on here and on other places regarding this, but no one's seems to be working & then not working like mine is. I'm hoping that since it comes and goes that i can simply just replace the solenoid and not have to worry about a rebuild.

If anyone has any insights or suggestions please let me know!

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I would try changing out the solenoid which should not cost that much if you can do it yourself and changing the filter while your in there. With that many miles the only answers that you will get is to rebuild the tranny. 

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9 hours ago, sha4000 said:

I would try changing out the solenoid which should not cost that much if you can do it yourself and changing the filter while your in there. With that many miles the only answers that you will get is to rebuild the tranny. 

Thanks, i should be able to replace it myself. I just need to make sure i buy/order the right one. 

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