Circuit Description

Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term and long-term fuel trim.

DTC P0171 is set when fuel trim is rich beyond a certain value. Possible causes are:

• Air induction system malfunction.
• Improper fuel pressure.
• Fuel injector restricted.
• Defective heated oxygen sensor No. 1.
• Defective Manifold Absolute Pressure (MAP) sensor.
• Defective Engine Coolant Temperature (ECT) sensor.
• Exhaust system leak.

DTC P0172 is set when fuel trim is lean beyond a certain value. Possible causes are:

• Improper fuel pressure.
• Fuel injector restricted or leaking.
• Defective heated oxygen sensor No. 1.
• Defective Manifold Absolute Pressure (MAP) sensor.
• Defective Engine Coolant Temperature (ECT) sensor.
• Exhaust system leak.