DTC P0173 - Bank No. 2, Fuel Trim Malfunction: Condition

WARNING: This page is about a different car, the 1997 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when fuel injection closed loop correction and learning correction are above specified value because of system malfunction. Possible causes are:

Fuel pressure regulator malfunction.
Fuel injector malfunction.
Fuel pump malfunction.
Engine Coolant Temperature (ECT) sensor malfunction.
Mass Airflow (MAF) sensor malfunction.
Left front oxygen sensor malfunction.
Purge solenoid valve malfunction.
Intake air system leakage.
Engine Control Module (ECM) malfunction.
Open or short in circuit between fuel injectors and ECM terminal No. 4U, 4AC or 4AK.
Intake Air Temperature (IAT) sensor malfunction.
EGR boost sensor malfunction.
PCV valve malfunction.