Engine Controls - MIL ON Fault Code 174/175

SI B 12 12 07
Engine Electrical Systems

August 2007
Technical Service

SUBJECT
S54 Service Engine Soon Light Illuminated: FC 174 and 175 Fuel System Diagnosis

MODEL
E46 (3 Series) M3 with S54 engine
E85 Z4 M Roadster and E86 Z4 M Coupe with S54 engine

SITUATION
Customer may complain of one of the following faults in conjunction with the Service Engine Soon Light being illuminated.

^ Rough idle

^ Engine idle observed higher than normal (approximately 900 RPM)

^ Hesitation while accelerating

^ Poor fuel economy

One of the following FC's may be stored in the DME:

^ FC 174 (AE) Fuel system diagnosis, cylinder 1-3

^ FC 175 (AF) Fuel system diagnosis, cylinder 4-6

When attempting to diagnose, the air mass sensor (HFM) signal deviates from specification at idle.

CAUSE
One of the following causes may be found:

^ Induction system diffuser is missing or removed changing velocity or direction of induction air path

^ Activated carbon filter removed or modified

^ Aftermarket unapproved air filter/cold air kit

^ Induction system air path disturbance, holes, cracks, separation of air duct

^ Redirection of the induction air path, collapsed, blocked, etc.

^ A velocity increase in the induction air path, air duct removed, missing, etc.

^ Modifications made to any part of the induction air path including the duct work mounted in the front bumper and grille area.

Note:
Air path disturbance can be defined as any modification to the induction system from the point where the air is entering the front of the vehicle to the cylinder head intake ports.

PROCEDURE

Inspect the air path for redirections and modifications. Remove the upper half of the air filter box to inspect for the removal of the air diffuser. Refer to illustrations.

E46 M3





NOT OK!
Air diffuser is removed causing disturbance in air path. If the diffuser is found defective or missing the entire air filter assembly lid will need to be replaced as a whole. The air diffuser is not available separately.





OK!
Air diffuser installed correctly.

E85 and E86 MZ4

Not OK!





1. Removal of the activated carbon filter will disturb the intake air path and allow hydrocarbons to escape the intake plenum when the vehicle is stationary not running. This activated carbon filter is a emission control device and should not be removed. If found removed or modified the entire air box assembly needs to be replaced. The activated carbon filter is not available separately

2. Air diffuser is removed causing disturbance in air path.

If either of the above items are found removed or modified the air filter assembly lid needs to be replaced. Both items are not available separately.





OK!

1. Activated carbon filter installed correctly

2. Air diffuser installed correctly

WARRANTY
Use of non-approved modifications or items will not be covered under the terms of the new vehicle warranty.





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