I recently purchased a 2019 d3 manual with 80 000 miles. I did 3000 miles without any significant issues. I commute daily (about 20 minutes commute) every day, and usually do longer drives on weekends (2 hrs +).
I occasionally get the “Reduced Engine Performance” light and most recently on the motorway (From France to UK = 12 hour drive) the occasional engine light.
The car RPMs sometimes oscillate at idle and it performs the occasional “jerk” (almost like a misfire) which can happen on the overrun or part throttle (I have not noticed this at WOT). This almost feel like a very small stab of the brakes.
I am writing this post to share my experience trying to understand the cause of these errors.
I receive the following codes after scanning with the Car scanner device:
P047100 – Exhaust Pressure Sensor A Circuit Range/Performance.
P00BC00 – Mass or Volume Air low A circuit Range / Performance – Air flow too Low. General Failure information. No Sub Type Information.
P20EE00 – SCR Nox Catalytic Converter Efficiency Below Threshold (Bank 1). General Failure information. No Sub Type Information.
P252F00 – Engine Oil Level Too High. General Failure information. No Sub Type Information.
P200977 – Intake Manifold Control Circuit Low (bank 1). Commanded Position Not Reachable.
These errors never clear, so I decided to attempt to diagnose the source of this issue. At this point, the car just clocked 84 000 miles, so I am going to assess all the engine sensors and check the looms for cleanliness or if there are any nicks or cuts.
The first sensor is the boost pressure sensor (31405341). This is located on the intake side of the engine and is held in by a T30? Screw. It is simple to remove, just need to be careful not to damage the connector.
This sensor seemed very dirty, I cleaned it using some brake cleaner and an air gun (careful not to blow into the sensor).
I then scanned the car again and it still came back with the same error codes. The “occasional jerk” is also still present. It seems like the engine feels a bit more crisp now (not by a lot) and the RPM no longer seems to fluctuate on idle.
The next step for me was to clean the pipe at the back of the engine, which leads to the exhaust pressure sensor (31319419).
The pipe is very accessible and came of quite nicely. Just need to be careful when removing the bolt that secures the sensor bracket not to drop it into the eternal abyss…
Upon inspection, after removing the sensor, it was found that the pipe was fully blocked with soot. Using a combination of lockwire, WD40, brake cleaner and a burner (very careful next to the flammable products!). I managed to clear that pipe so that I could blow air through it. This would have been easier using a compressed air gun, but I did not have one handy at the time…
I re-installed the pipe and to my disappointment, the errors were still present.
I then tried disconnecting both batteries (to try and reset the car), this also did not work. This was followed by disconnecting the ECU (after re-disconnecting the batteries), which is located behind the front left wheel trim inside a waterproof box.
From the picture you can see how dirty this area of the car gets. I did my best to clean everything and the electrical components with electrical cleaner.
The errors were still present on the scan after that, despite trying to clear them. I then took the car for a 20 minute drive and it drove fine, but due to the intermittent nature of the “occasional jerks” and the Reduced Engine Performance lights, it is still far too early to assess what is going on.
Summary (09/01/2025):
- Cleaned Boost Pressure Sensor
Idle fluctuations possible gone but the “occasional jerk” is still there.
Summary (11/01/2025):
- Cleaned Exhaust Pressure Sensor pipe and sensor
- Disconnected Batteries
- Disconnected Batteries, ECU and gave the ECU pins a clean.
Still no idle fluctuations or Reduced Engine Performance/Engine Lights.