Circuit Description

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

Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term and long-term fuel trim. DTC P0171 and DTC P0172 apply to bank No. 1. DTC P0174 and DTC P0175 apply to bank No. 2. Heated A/F sensors are located on exhaust manifold above catalytic converters. A/F sensor for cylinders No. 1 and 4 is referred to as bank No. 1 sensor No. 1. A/F sensor for cylinders No. 2 and 3 is referred to as bank No. 2 sensor No. 1. A/F sensors may also be referred to as A/F ratio sensors.

DTC P0171 and/or DTC P0174 is set when fuel trim is driven rich beyond a certain value. Possible causes are:

Air induction system malfunction.
Fuel injector restricted.
Defective Mass Airflow (MAF) meter.
Defective Engine Coolant Temperature (ECT) sensor.
Improper fuel pressure.
Exhaust system leak.
Air/Fuel (A/F) sensor circuit is open or shorted.
Defective Air/Fuel (A/F) sensor.
Vehicle is ran out of fuel.
Defective ECM.

DTC P0172 and/or DTC P0175 is set when fuel trim is driven lean beyond a certain value. Possible causes are:

Fuel injector restricted or leaking.
Defective Mass Airflow (MAF) meter.
Defective Engine Coolant Temperature (ECT) sensor.
Improper fuel pressure.
Exhaust system leak.
Air/Fuel (A/F) sensor circuit is open or shorted.
Defective Air/Fuel (A/F) sensor.
Vehicle is ran out of fuel.
Defective ECM.