Tech notesDirty air filter, air filter housing or Mass Air Flow (MAF) sensor, or faulty MAF sensor are common causes for the P0170 code.
When is the code detected?Fuel injection system does not operate properly or the amount of mixture ratio compensation is not correct
P0170 Bmw DescriptionWith the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The Engine Control Module (ECM) calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECM judges the condition as the fuel injection system malfunction and light up the Malfunction Indicator Light (MIL) (2 trip detection logic).