DTC P0171, P0172, P0174 Or P0175: Fuel Trim System & DTC P1130, P1131, P1132, P1150, P1151 Or P1152: Ho2S Not Switching: Condition

WARNING: This page is about a different car, the 2002 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0171 is set when right bank fuel trim system is too lean. DTC P0174 is set when left bank fuel trim system is too lean. DTC P0172 is set when right bank fuel trim system is too rich. DTC P0175 is set when left bank fuel trim system is too rich. DTC P1130 is set when right bank fuel control system has reached maximum compensation for lean or rich condition and front heated oxygen sensor HO2S is still not switching. DTC P1150 is set when left bank fuel control system has reached maximum compensation for lean or rich condition and front heated oxygen sensor HO2S is still not switching. P1131 is set when right bank fuel control system is correcting rich for an overly lean condition and front HO2S voltage is less than .45 volt. P1151 is set when left bank fuel control system is correcting rich for an overly lean condition and front HO2S voltage is less than .45 volt. P1132 is set when right bank fuel control system is correcting lean for an overly rich condition and front HO2S voltage is more than .45 volt. P1152 is set when left bank fuel control system is correcting lean for an overly rich condition and front HO2S voltage is more than .45 volt. Possible causes are:

Excessive fuel pressure.
Leaking fuel injector.
Leaking pressure regulator.
Low fuel pressure or running out of fuel.
Contaminated fuel injector.
Oil overfill.
Incorrect cam timing.
Incorrect cylinder compression.
Exhaust leaks upstream of or near HO2S.
Air leaks between Mass Airflow (MAF) sensor and intake manifold.
Vacuum leaks.
Restricted air inlet.
PCV system malfunction.
Fuel purge system malfunction.
Improperly seated engine oil dipstick.
Leaking EGR valve gasket.
Stuck open EGR valve.
Leaking EGR valve diaphragm.