Flashing CEL & Rough Idle on Jaguar XF Raises Red Flags

Had similar symptoms with a 2019 Jaguar XE P250. The flashing check engine light combined with rough idle often points to knock sensor issues, but in my case it turned out to be a loose wiring harness connection to the knock sensor rather than the sensor itself. The engine knock was most noticeable at idle, and poor performance was significant during acceleration. Auto repair revealed the connector had partially separated due to engine vibration, causing intermittent signal loss to the ECU. The repair required removing some engine covers to access the harness, cleaning the connector pins, and securing the connection properly. This is a serious issue that needs prompt attention since running with faulty knock sensor input can lead to engine damage. When the knock sensor stops communicating properly, the ECU defaults to a conservative timing map, explaining the significant drop in fuel economy you are experiencing. While 800€ for just diagnostics seems steep, dealing with sensor communication issues requires proper testing equipment. Suggest getting a second opinion from a certified shop that specializes in Jaguar electronics. The actual repair cost varies based on whether its just a connection issue or if the knock sensor needs replacement.

Thanks for sharing your experience. Wondering how much you ended up paying for that wiring harness fix at the end? My ignition timing is still off and fuel efficiency hasnt improved, so I am trying to gauge what to expect cost-wise. Also, has everything been running smoothly since your repair or have you noticed any related car problems popping up?

Since getting the knock sensor issue fixed, my Jaguar XE has been running perfectly with no warning lights or engine problems. The repair was straightforward, just 95€ to clean and secure the loose connector. The malfunction indicator cleared immediately after the fix, and fuel economy returned to normal within two tank fills. The rough idle and engine knock symptoms completely disappeared once the wiring connection was properly restored. Looking back, I was fortunate it was just a connection issue rather than needing a full knock sensor replacement, which would have cost significantly more. My advice is to get it checked soon, the drop in fuel efficiency you are experiencing likely means your engine is still running in protective mode due to the faulty knock sensor input. Running too long in this state isnt ideal for engine longevity.

Thanks for the input. I took the car to a different mechanic who actually specializes in engine management systems. The diagnostic fee was reasonable at 120€, and they found the exact same issue, a damaged wiring connection to the knock sensor. Total repair came to 180€ including labor, much better than the 800€ quote from the first place. The malfunction indicator cleared right after the fix, and the engine runs smooth now. Fuel efficiency is almost back to normal after about 4 days of driving. Was definitely worth getting a second opinion rather than jumping into expensive repairs. The specialist mechanic showed me the corroded connector and explained how these issues affect ignition timing and overall engine performance. Good learning experience, though I wish I had investigated the poor performance symptoms earlier before my fuel costs shot up.