MiTo Engine Light + Rough Running = Water Sensor Issue

Had similar symptoms with my 2015 Alfa Romeo Giulietta 1.4T. The check engine light combined with rough running turned out to be a faulty coolant temperature sensor causing incorrect fuel mixture. The car sensor was sending wrong readings to the ECU, leading to poor performance and irregular idle. Auto electronics testing revealed the issue was not the sensor itself, but corroded wiring connections at the sensor plug. The electrical fault made the readings unstable. A proper sensor testing procedure should include checking both the component and its connections. In this case, cleaning and reseating the connector solved the issue. Would have been a much bigger repair if the mechanic had just replaced parts without proper diagnostics. This type of sensor fault is common in these engines and can mimic more serious problems. Best to have it checked soon as incorrect temperature readings can affect engine performance and fuel economy. The repair itself is straightforward once properly diagnosed.

Thanks for sharing your experience with the Giulietta. Currently facing a moisture sensor problem in my MiTo and was worried it might be something major. Good to know it could be just connection issues. The rough running in my case sounds very similar. The mechanic initially suggested a full sensor replacement, but after reading your post, I will ask them to check the wiring and connections first. Mind sharing how much the repair cost in your case? Also curious if you had any recurring sensor issues since getting it fixed?

After having the sensor malfunction investigated, the repair ended up being quite simple. The mechanic found the moisture sensor issue was indeed caused by a faulty cable connection, just like I suspected. Total cost came to 95 Euro for cleaning and fixing the plug connection. The malfunction indicator hasnt returned since the repair was completed. No more sensor faults or rough running issues. Auto electronics testing confirmed the sensor is now sending correct readings to the ECU. Looking back, requesting a thorough check of the wiring connections before replacing parts saved considerable money. When these sensor issues appear, its often the connections rather than the sensor itself causing problems. If you get similar symptoms again, definitely have them check the wiring and plugs first. A proper diagnostic of the complete sensor system, including all connections, can prevent unnecessary parts replacement.

Thanks everyone for the helpful replies. Just wanted to update on how it turned out with my MiTo. Took it to a different mechanic who actually listened when I mentioned checking the connections first. They found corroded wiring near the moisture sensor that was causing the malfunction indicator to trigger. The repair was straightforward, they cleaned the connections and applied some protective coating to prevent future electrical fault issues. Total bill came to 120 Euro, which included the diagnostic work. Car has been running smooth for the past week with no warning lights. The auto electronics test they ran afterward showed all sensors working properly. Definitely learned to be more specific about checking connections before agreeing to full sensor replacements.