VW Fox Diesel Warning Light + High Fuel Use Troubles

I had similar symptoms with my 2009 VW Polo TDI. The check engine light appeared along with rough idling and increased fuel consumption. After diagnosis, it turned out the knock sensor connector had corroded, causing intermittent signal issues. The repair involved replacing both the knock sensor and its wiring harness due to degraded insulation. This was a more serious issue than initially expected because the faulty signals were causing the engine management system to run rich fuel mixtures as a protective measure. The malfunction indicator stayed on for several days before I got it checked, which was a mistake. Waiting too long with these symptoms can lead to additional engine stress and even poorer fuel efficiency. Key checks worth doing: Scan for error codes, Inspect the knock sensor connector for corrosion, Check the wiring harness for damage, Test the sensor resistance values The knock sensor issue can sometimes mask other problems, so a proper diagnostic scan is essential. Avoiding this repair can lead to long-term engine damage and continued poor performance.

Thanks for sharing your Polo experience, those symptoms do sound very similar to my Fox issue. I finally got my car fixed last week and the mechanic confirmed it was indeed the knock sensor. Did the repair completely solve your warning light and fuel consumption problems? Also, if you remember, could you share how much the total repair ended up costing? I paid 380€ for the complete job including parts and labor, wondering if that was reasonable. One thing to note, I noticed some hesitation during cold starts is still present occasionally, though much less severe than before. Have you experienced any lingering issues after your repair?

Had my car back from the shop a while ago and can confirm the knock sensor repair completely resolved the issues. The warning light is now permanently off and fuel consumption returned to normal levels. My repair bill came to 95€ since they only needed to fix a faulty cable connection to the sensor rather than replacing the entire unit. The cold start hesitation you mentioned is interesting, I experienced nothing like that after my repair was done. If you are still getting occasional rough starts, might be worth having the mechanic take another look. Sometimes initial car problems can mask other underlying issues that only become noticeable once the main fault is fixed. Making sure the knock sensor gets fixed promptly was definitely the right call. These engine knock detection systems are crucial for preventing serious engine damage. Since the repair, my engine has been running smoothly with no check engine lights or any other warning signs. Just keep monitoring those cold starts, while the knock sensor repair often resolves most issues, any persistent symptoms should be checked to maintain optimal engine performance and prevent future car problems.

Thanks everyone for the helpful replies. I took my Fox to the shop last Tuesday after seeing these responses. The mechanic found heavy corrosion on the knock sensor wiring, just like some of you mentioned. The sensor itself was also damaged. Total repair cost was 380€ including a new knock sensor, wiring harness and labor. The malfunction indicator is now off and fuel efficiency has improved significantly. My engine runs much smoother overall. However, even after the auto repair work, I still notice slight hesitation during the first cold start of the day. The mechanic adjusted the ignition timing which helped, but said I might need to get the fuel injectors cleaned if it continues. For now, I will monitor how it runs over the next few weeks. Really glad I got this fixed promptly instead of waiting. Learning about proper engine knock detection and prevention was eye-opening. Will definitely pay more attention to warning signs in the future to avoid potential engine damage.