This may help - from TIS:

P2279 The control unit recognises a mechanical malfunction of the following component via an internal evaluation logic:
Intake system

The following test steps must be performed in the given order. If a fault is found in one test step, the subsequent test steps can be skipped.
Function Checks
•Verify mechanical system functions/components
Intake system
Check intake system/charge air hoses for leaks (secondary air, porosity and blockages)
Check the hose clamps at the intake-air system / charge-air system for correct fitting.
Check connected hoses and tubes for kinks, damage etc.
Check air filter for fouling and correct mounting.
Check air mass meter for fouling.
Exhaust-gas turbo charger
Exhaust system
Refer to Table B-023 Check: Vacuum Supply System
Read and (if applicable) apply Field Remedy 1779
Actuator Tests
•Select the following Functional System:
Electronic Diesel Injection System EDC 16C9, Z 17 DTL, Z 17 DTH
•Perform the following Actuator Tests:
Refer to Table B-014 ACTUATOR TEST T001 EGR Solenoid Test (Below):


Work Order Description Nominal Value
•Ignition ON
•Engine idling

•Press corresponding key in the system main menu to call up Actuator-Test functions, select the desired test and confirm with ENTER . Follow the instructions in the diagnostic tester display.
•After the test is started, the corresponding component can be actuated using the soft keys.

•Press soft key INACTIVE
Mass air flow sensor signal is greater than 35 kg/h
•Press soft key ACTIVE
Mass air flow sensor signal is less than 35 kg/h
Note:
To protect the component, the duration of the actuator test is limited.
Concerned Terminals:
ECM: 9, 34, 51, 57 (XC11)
Reply to: