Engine Performance (A8)Pregunta 93 de 120
An oxygen (O2) sensor in the exhaust provides feedback to the PCM about:
a.Engine oil level
b.Coolant temperature
c.The air-fuel ratio (rich or lean)
d.Ignition timing advance
Explicación
The oxygen sensor measures residual oxygen in the exhaust, telling the PCM whether the mixture is rich or lean so it can adjust fuel trim. A lazy or failed sensor degrades fuel control and emissions. Wide-band sensors report the actual ratio rather than just rich/lean.
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- A diagnostic trouble code (DTC) of P0301 indicates:
- Technician A says a vacuum leak causes a rich condition. Technician B says a vacuum leak adds unmetered air and causes a lean condition, especially at idle. Who is correct?
- Technician A says a positive long-term fuel trim of +20 percent means the PCM is adding fuel to correct a lean condition. Technician B says positive trim means the engine is running rich. Who is correct?
- Technician A says a rich air-fuel mixture can raise tailpipe CO and HC. Technician B says the oxygen sensor helps the PCM keep the mixture near stoichiometric. Who is correct?
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