F5, F6 Secondary-Air Malfunction

From Bavarian Technic

Jump to: navigation, search


F5 & F6 - Secondary Air system fault

  • DME version MS43


The service engine soon lamp is illuminated. After a short test on the vehicle, faults F5 and F6 are stored in the DME control unit.

  • F5 - Secondary air system, air flow too low, bank 1.
  • F6 – Secondary air system, air flow too low, bank 2.
  • P-code – P0491 and P0492


A malfunction within the secondary air system is present or intermittently occurs. If one of the secondary air components is malfunctioning, the service engine soon lamp will illuminate. Possible failures within the secondary air system could be the air pump, one-way valve, activation solenoid valve, or the air passage within the cylinder head.


Verify operation of the secondary air pump through activations. With a hand held vacuum pump verify the operation of the one-way valve; actuation can be felt at the valve. Connect a vacuum gauge to the activation line at the one-way valve from the activation solenoid. Run the engine and activate the solenoid valve via the activations menu. Monitor the vacuum gauge, engine vacuum of greater than 15 in. of vacuum should be visible on the gauge. Intermittent malfunctions within the secondary air system are very common. Moisture collecting in the one-way valve can cause it to malfunction in cold temperatures. The most common component to have intermittent faults is the activation solenoid. When checking the operation of the activation solenoid, be sure to inspect the vacuum line to/from the activation solenoid and one-way valve. Some secondary air systems have eliminated the activation solenoid and designed a one-way valve that will only open when air pressure is applied by the secondary air pump.

Personal tools