Toyota Prius EGR monitor

Eric Owner/Technician Grand Rapids, Michigan Posted   Latest  
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Driveability
P0401 — EGR "A" Flow Insufficient Detected

Simple issue, EGR valve not responding to command from PCM. Easy to see desired and actual, actual always at zero. Removed EGR motor on top of valve and the pintle is seized. No problem, replace EGR valve, perform active test, all is good. Here is my question, it passed the EGR monitor very quickly. Does Toyota only want to see actual and desired matching each other for a passing monitor? Prius is unique in that the gasses pass through a cooler just prior to entering the actual valve. This cooler can get restricted with carbon and oil, especially on high mileage engines. This obviously limits the amount of exhaust gas entering the combustion chamber. Is it also looking at AFS and/ or O2 sensors for validation? There is zero spark knock, vehicle runs very well. Confirming repair with a passing EGR monitor is quick but would like a bit more confirmation that system is indeed repaired as needed. Note- changing the EGR cooler is a major pain and the coolers are a bit pricey, if it needs it fine, but as a cover your ass job, would only want to do it if necessary. 

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Edward Owner
San Antonio, Texas
Edward Default
 

Good morning Eric What's the VIN number

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Eric Owner/Technician
Grand Rapids, Michigan
Eric Default
 

Sorry, 2010 Prius. All Gen 3's use this set up.

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Matt Technician
Lawrence, Massachusetts
Matt Default
   

It seems it looks at the MAP sensor From SI: MONITOR DESCRIPTION "The ECM monitors the pressure inside the intake manifold while opening and closing the EGR valve during fuel cut operation. If there is no change in the manifold absolute pressure sensor value, the ECM interprets this as a malfunction in the EGR valve assembly, illuminates the MIL and stores the DTC (2 trip detection…

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Eric Owner/Technician
Grand Rapids, Michigan
Eric Default
 

All that had been performed about 6 months ago. I certainly felt that if it passed the monitor we're good to go but I think I'll monitor both egr actual, requested and map values on the Techstream during graphing and watch for the necessary change in map. Got another gen 3 in now for other work, my guinea pig.

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