Peugeot 406 Automatic Transmission Issue

Sounds nasty. I had something similar happen with my old Opel Astra, though it was the coolant temperature sensor throwing everything off. The symptoms were almost identical – limp mode, dodgy shifting, the works. Have you checked for any signs of a leak around the radiator or oil cooler? Maybe the pressure sensor is working fine, but it is simply reading low pressure? Inspecting the wiring and connections to the sensor is a good call, but also look around the surrounding components.

A coolant temperature sensor, huh? Interesting. I'll have to look into that too, thanks! When you say 'signs of a leak,' what exactly should I be looking for?

With a leak, think about staining, gunk buildup, anything that looks out of the ordinary. However, since it's related to pressure and transmission, I'd say it's time for a workshop. It's very likely to be a broken wire connection, but you risk damaging the transmission even further if it turns out to be something else. In my case, I had to change the automatic transmission fluid and the coolant temperature sensor.

Thanks a lot! You were right, it ended up being a defective cable connection to the oil pressure sensor like I thought. The mechanic charged me 95€ to replace it. I appreciate the advice!