Question

Technician A says that manually opening an exhaust gas recirculation (EGR) valve with a vacuum pump or scan tool will cause the engine to idle roughly or stall. Technician B says that blocking the EGR valve passages will have no effect on the OBD-II. Who is correct?

Answer 1

Technician A is correct

Step-by-step explanation:

Manually opening the Exhaust Gas Recirculation (EGR) valve with a vacuum pump or scan tool will cause the engine to idle roughly or stall.

The EGR valve recirculates a portion of the exhaust gases back into the intake manifold to lower combustion temperatures and reduce NOx emissions. Opening it manually introduces extra inert gases into the intake air-fuel mix, disrupting normal combustion and causing unstable idle or stalling.

Technician B is incorrect. Blocking the EGR valve passages will set an EGR related diagnostic trouble code (DTC) and illuminate the check engine light. This is because the OBD-II system monitors the EGR system functionality and detects issues like blockages or flow problems.

So in summary, manually opening the EGR valve interferes with proper engine idle, while blocking EGR flow triggers the OBD-II system diagnostic monitors and turns on the check engine light.