QuestionWhat is this modulator used for?
What are the meaning of P, R and Q letter on it?
What is the purpose of the filter inside the modulator? If this filter got clogged, what will be the result?
About DTC P0401 "Exhaust Gas Recirculation Flow Insufficient Detected". What sensor detected this flow and sent its status to the PCM?
If it it possible, please give me a short lession about the EGR vacuum modulator.
Thank you very much.
AnswerThe vacuum modulator controls the EGR valve with a vacuum switching valve to turn the egr valve on and off, the entire process in sontrolled by the onboard computer, the egr valve is on or off depending on driving conditions, it is supposed to be on during cruise conditions, never at idle or full throttle.
The computer regulates egr gases based on several input signals on the engine such as rpm,vehicle speed, engine load,coolant temperature etc.
The DTC PO401 is stored in the computer because the egr exhaust gas temperature sensor doesn't see a predetermined temperature programmed into it because of insufficient egr gas flow into the intake manifold, this will turn the check engine light on.
You can check the vacuum modulator by removing it and if you are able to blow air through it from the bottom port it has an internal leak and needs to be replaced.
