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I have a P20C9 code. 2011 Isuzu NPR 3.0 4jj1. Fixing myself.

I have a P20C9...

I have a P20C9 code.

Mechanic's Assistant: What's the make/model/year of your truck? Engine type?

2011 Isuzu NPR 3.0 4jj1

Mechanic's Assistant: Are you fixing your truck yourself? What have you tried so far?

Fixing myself. Cleared codes four times but it keeps coming back after a while

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Answered in 5 days by:
8/21/2018
Technician: Jeremy, Certified Truck/Bus Technician replied 4 years ago
Jeremy
Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 4,370
Experience: ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, Network Engineer specializing in CAN faults, Aftertertreatment, and vehicle communications
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Customer reply replied 4 years ago
I do and I'm able to understand trouble shoot dialog in a high level.
Technician: Jeremy, Certified Truck/Bus Technician replied 4 years ago

The fault is for the Diesel Exhaust Fluid Control Module. Here is what aggravate about this particular fault. A scan tool is needed to diagnose it further.

The fault is telling you that the particular module is seeing a fault and it has a fault stored inside of it. It is Isuzu's way to get the truck into their shop for the issue. Not really in the US, but other countries (like the European union) where they are not allowed to work on regen systems. It is heavily controlled in other areas.

When the scan tool gets connected, the tech can see the fault in that module and then see what is causing it. It can be simple things like contaminated DEF (which you can check with a DEF test kit) to a dead spot on the DEF tank float to more serious items like bad NOx sensor or plugged DEF injector.

CLICK HERE for the diag tree for the particular fault you have. You can see it keeps referring to checking the scan tool and running the diagnostic within the controller for the DTC inside of it. I don't recall the dash ever giving DTCs that are in the fault controller. If you have another one that popped up, give that as well. Otherwise, this will need the scan tool to dig further. It is one of the most aggravating things about this fault with Isuzu.

Jeremy
Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 4,370
Experience: ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, Network Engineer specializing in CAN faults, Aftertertreatment, and vehicle communications
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Jeremy
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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 4,370
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