Yesterday afternoon after the vehicle had been sitting for over ten hours, a Engine Malfunction - Reduced Output warning was received. It was gone before I could really even see what it was. The vehicle ran fine on the way home, approximately 15 miles.

After sitting overnight, this morning again the warning was received. When I got to work, I used Carly to pull any DTCs. Only 04BC0 was present. I cleared it and went for a quick drive.

The vehicle ran fine and no warnings were received. I stopped and started the engine twice. After approximately 20 miles and after coming to a stop at a traffic light for approximately 30 seconds, multiple engine malfunction warnings were received. They would come on for about one second and then go away for five seconds. Once I started driving, everything was fine.

When I parked again, I used Carly to get the DTCs. This time:

004BC0 - Air Flow Meter - Signal too low
004BC2 - " - short circuit

Recent work less than 5k miles ago:

Transmission fluid and filter replacement
Active SCR tank replaced
SCR metering module replaced
Diesel fuel filter replaced
Engine oil and filter replaced
Engine air filter replaced

Any ideas on how I should proceed? Does not seem to be a common fault although there is a SIB regarding the HFM.

ETA: The vehicle sat for several hours since this morning. Took it out at lunch on nearly the same route and routine as this morning. No issues. The only thing I did in between was pull the engine cover off, look at the HFM and move the connector around. I read on another forum that a poorly connected HFM could cause issues.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim