XT4 Diesel Rough Running Points to QDC Sensor Issues

As someone with moderate experience working on diesel engines, I dealt with nearly identical symptoms on a 2018 XT5 Diesel last winter. The fuel economy dropped significantly and the engine had similar rough running issues, especially during cold starts. After checking the system diagnostics, my workshop found that drift compensation values were way off on one injector. They performed detailed testing which revealed a faulty injection valve. The car sensors were picking up the irregular fuel delivery pattern, triggering the check engine light. The fix required replacing the defective injector and performing a complete system reset to clear the compensation adjustment parameters. Total repair cost was 515€ including parts and labor. Since the repair, the engine has run smoothly with no further issues. To provide more specific advice about your case: What is the current mileage on your XT4? Have you noticed any changes in fuel consumption? Does the rough running improve once the engine reaches operating temperature? Can you share the specific error code from your diagnostics? This information would help determine if your situation matches what I experienced and whether you might be looking at a similar repair path.

Last service was done at 93000 KM and my current mileage is 94981 KM. Thanks for sharing your experience. The symptoms match exactly, fuel economy dropped about 15% and the rough running does improve after warmup. The diagnostic code I get is P0263, and fuel consumption increased from 6.8L to around 7.8L per 100km. The compensation values shown in my scanner are beyond typical ranges according to the workshop manual. Since posting, I had the airflow sensors tested and they check out fine, so the fuel injection system seems the likely culprit. I will have the injectors tested as you suggested to identify which one might be failing.

Thanks for providing those details. Your symptoms are nearly identical to what I experienced, especially that 15% fuel economy drop and the P0263 code. My compensation values were also out of normal range before the repair. The fact that your airflow sensors tested good narrows it down further. In my case, cylinder 1 injector was the problem, and the onboard diagnostics kept trying to compensate for its irregular spray pattern. This matches with your P0263 which specifically relates to cylinder 1 injection issues. Since our vehicles are similar and showing the same patterns, I strongly suspect you are dealing with the same injector problem I had. The drift compensation keeps trying to adjust for the failing injector, but cant fully correct it, hence the rough running and increased fuel consumption. One tip from my experience: when they replace the injector, make sure they perform a complete system reset to clear all the accumulated drift compensation values. My workshop initially skipped this step and the engine still ran slightly rough until they did the full reset procedure. The repair cost might be in a similar range to what I paid (515€), though prices vary. Let us know what they find when you get it checked.

Following up here, I booked the car in for next Tuesday and will definitely make sure they do the complete system reset after replacing any parts. Your details about the compensation values and P0263 code really helped confirm what I was suspecting about the injector. The workshop actually called to say they regularly see this issue with similar mileage on these engines. They quoted 490€ for the repair including the full reset procedure, which seems reasonable based on your experience. Interesting that the rough running behavior improves after warmup in both our cases. This whole situation has taught me to pay more attention to changes in fuel economy as an early warning sign. The onboard diagnostics definitely helped pinpoint the issue, makes diagnosis much more straightforward compared to older vehicles. Will update once the repair is done to confirm if it was indeed the same injector issue you experienced. Thanks again for all the detailed feedback.