Initial Inspection and Diagnostic Overview

Hint 1: The exhaust gas purification performance will worsen if there is a malfunction of the heated oxygen sensor.

Hint 2: If the heated oxygen sensor output voltage deviates from the standard value even though the results of the checking of the heated oxygen sensor are normal, the cause is probably a malfunction of a component related to mixture control.

[Examples]
1. Malfunction of an injector.
2. Air leakage into the intake manifold from a leaking gasket.
3. Malfunction of the intake air temperature sensor, the manifold absolute pressure sensor, or the engine coolant temperature sensor.