Is P0138 the front or rear oxygen sensor?

[SanClara]

P0138 is the rear oxygen sensor. Below is an introduction about the engine assembly: 1. Introduction: The engine assembly, also known as the engine, is a machine capable of converting one form of energy into another more useful form of energy. 2. Principle: It usually converts chemical energy into mechanical energy (the conversion of electrical energy into mechanical energy is referred to as an electric motor). Sometimes, it applies to both power generation devices and the entire machine including the power unit, such as gasoline engines and aircraft engines. 3. Development: Looking back at the history of engine creation and development, it has gone through two stages: external combustion engines and internal combustion engines.