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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3304
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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I have a 2008 isuzu npr showing code p0401 egr valve has

Customer Question

i have a 2008 isuzu npr showing code p0401 egr valve has been replaced and no restrictions in the ports. the same vehicle dies periodically at idle with no codes truck starts back up right away so not running out of fuel
Submitted: 2 years ago.
Category: Medium and Heavy Trucks
Expert:  Pete replied 2 years ago.
My name is ***** ***** I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
My info is limited on your model here but I see no one else has responded and thought I would see if I can help here.
The code P0401 indicates a fault with EGR flow itself.If there is an issue with the flow from the egr valve itself or the exhaust is plugged to where the egr is not pulling enough of the exhaust this will cause this code to set and is most common.
I would check over the exhaust and intake ports for the egr valve and make sure no damage or blockage is found.
If an issue is found it will need corrected.If this is checked and all found to be o.k. let me know.
Thanks Pete
Customer: replied 2 years ago.
I already said the ports arent plugged do you know how the computer determines the flow that is the info i want
Expert:  Pete replied 2 years ago.
On this model unfortunately I don't know how this computer monitors the flow rate.I will open your question up for others here to see if anyone else can assist further on this.
I will have to open this question up for others here to see if they can assist further on this as someone else here may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.
Thanks Pete
Expert:  Jeremy replied 2 years ago.
Check your MAF sensor. It is what detects the EGR flow.
I have included the info for you code below. This is direct from the Isuzu Diagnostic Technician's Portal so the links will not work inside the document for you.
Expert:  Jeremy replied 2 years ago.
I see you viewed this. Is there anything else I can asist you with?
Customer: replied 2 years ago.
I appreciate the info but the truck has not been back for any further testing may be here tomorro or the following tuesday
Expert:  Jeremy replied 2 years ago.
I thought I would check in just in case.
Customer: replied 2 years ago.
Good afternoon do you know what value the maf shoud read when the egr self test is done on board it reads 16.9- 18 g/s
Expert:  Jeremy replied 2 years ago.
If that is the MAF sensor reading, it is bad. It is supposed to be less than 11 on that sensor and you are at 16.9. I would replace the sensor.

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