haraldsilber2
Siena automatic transmission implausible shifting
Summary of the thread
A 2010 Fiat Siena 1.3 diesel is experiencing erratic shifting and is stuck in emergency mode, with the transmission indicator light on. The issue may be linked to worn-out transmission oil, potentially caused by undervoltage affecting the transmission control unit. A suggested solution is to have the transmission oil checked and replaced, which resolved the problem in this case, restoring smooth shifting.
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4 comment(s)
haraldsilber2 (community.author)
Undervoltage, huh? Interesting. Now that you mention it, the car has been struggling to start sometimes. You think that could actually mess with the transmission? What exactly was the issue with yours?
sarahblade10
Yeah, on mine, the low voltage was messing with the transmission control unit. It couldn't properly regulate the oil pressure, hence the weird shifting. I'd suggest getting it checked at a workshop. They'll probably recommend a transmission flush and oil replacement.
haraldsilber2 (community.author)
Thanks a lot! Workshop confirmed it was worn-out transmission oil due to undervoltage. 240€ later and a transmission oil change, it's shifting smoothly again. You nailed it!
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FIAT
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SIENA
sarahblade10
I had something similar happen with my Siena (though it's a different year). Was the shifting rough, and did you notice any undervoltage issues beforehand? Like, did the lights dim unusually or the starter sound weak?