Peugeot 407 automatic transmission erratic shifting

I'm having issues with my 2009 Peugeot 407 diesel. It has 191587 km. The automatic transmission is behaving erratically, shifting in ways that don't seem right, and the transmission indicator light keeps popping on. Sometimes it doesn't shift when it should, and occasionally it even goes into emergency mode. Could it be the oil? Anyone else had the same issues?

4 comment(s)

I know that feeling all too well! I had something similar occur with my 407. The symptoms sound eerily familiar. Have you checked your car's voltage recently? In my case, undervoltage was the culprit. Is the battery old?

Thanks for your quick reply! Undervoltage, really? I hadn't considered that. How did undervoltage cause issues with your automatic transmission? And how did you figure it out in the first place?

Well, it's kind of like your car's brain (the ECU) getting scrambled signals when the voltage drops too low. The automatic transmission relies on precise electronic controls. If those controls aren't getting the juice they need, things go haywire. In the end I went to the workshop and they replaced the oil after diagnosing the undervoltage as the reason for the oil degradation.

Following your advice, I took the Peugeot to the workshop. You hit the nail on the head! It was indeed undervoltage that had prematurely worn out the transmission oil. Replacing the oil did the trick, for 240€! I really appreciate your help!

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