Fiat Doblo Knock Sensor Fault

Ah, the dreaded knock sensor! I had a similar experience with my old Opel Corsa, though it was a diesel. The symptoms were almost identical: warning light, poor fuel efficiency, and an unstable idle. In my case, it turned out to be corrosion within the connector itself, even though it looked fine at first glance. The ECU was pulling timing due to the erroneous signal, hence the increased fuel consumption and rough running. Have you checked the resistance of the sensor itself? And what DTC are you getting?

Thanks for the info! I haven't checked the resistance yet; I'll need to get my multimeter out. The DTC is P0325, which is the generic code for 'Knock Sensor 1 Circuit Malfunction'. Is there a specific resistance range I should be looking for?

P0325 confirms the knock sensor circuit issue. I don't recall the exact resistance range for your specific sensor, but a quick search of the Fiat forums should yield the correct figures. Given your mileage and the age of the vehicle, and considering that you've already visually inspected the wiring, I'd say it’s prudent to take it to a qualified workshop for a thorough diagnosis before throwing parts at it. It could be a faulty sensor, damaged wiring, or even a problem with the ECU itself.

Thanks again for the advice. I took it to a mechanic, and you were spot on it was the connector. They cleaned up the contacts and replaced a small section of corroded wire. Cost me about 95€ all in. Runs like a dream now!