Exhaust EGR (Exhaust Gas Recirculation) Systems 2

Question 1

Which sensor is most commonly used to directly monitor EGR flow rate?

Accepted Answer

EGR differential pressure sensor

Answer

The EGR differential pressure sensor measures the pressure drop across a restriction in the EGR circuit to calculate actual exhaust gas flow rate.

Question 2

What OBD-II diagnostic trouble code most commonly indicates insufficient EGR flow?

Accepted Answer

P0401

Answer

P0401 is the standard OBD-II code for EGR Flow Insufficient Detected, meaning the PCM commanded EGR flow but measured less than expected.

Question 3

Under which operating condition does the PCM typically disable EGR flow completely?

Accepted Answer

Wide-open throttle (WOT) acceleration

Answer

EGR is disabled at wide-open throttle to allow maximum airflow into the combustion chamber without dilution, ensuring full power output.

Question 4

In a high-pressure EGR system, where is exhaust gas extracted from?

Accepted Answer

Upstream of the turbocharger turbine inlet

Answer

High-pressure EGR taps exhaust gas upstream of the turbocharger turbine, where exhaust pressure is highest, providing a strong pressure differential to drive recirculation.

Question 5

What condition typically results from EGR cooler failure?

Accepted Answer

Coolant contamination of the intake and white smoke from exhaust

Answer

A cracked EGR cooler allows engine coolant to enter the intake manifold, producing white smoke as coolant burns in the combustion chamber and risking serious engine damage.

Exhaust Practice Test

Exhaust Practice Test

Exhaust EGR (Exhaust Gas Recirculation) Systems 2