codes P203F and P0128

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upflying

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While sitting completely stopped and idling for one hour on an incline on Interstate 80, a check engine light popped on. After I got home, I pulled the codes and discovered P203F is low DEF and P0128 is engine operating cooler than it should. Dealer wants $180 plus labor and parts to diagnose this. Could idling for one hour in cold weather cause the cold engine code? Could the incline I was stopped on cause the low def code? Def tank gauge shows about 1/3 remaining. I'm ready to clear the codes myself an tell the dealer to screw it.
My truck is a 2018 CTD, crew cab, shortbed...29,000 miles.
 

18CrewDually

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That's what I'd do. I'd top it off with fresh DEF and clear the codes. I'd also stop idling it for an hour! ;)
If you have to idle, use the cruise control buttons and tach it up to 1500 rpm.
 
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upflying

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Thanks, I was stopped in gridlock traffic due to the storm over Donner Pass.
Idling was needed to keep the heater going, I'll increase the idle speed if it happens again.
 

mtnrider

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Fill it with DEF and reset the codes. I'd bet they won't come back...

.
 

06 Dodge

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Thanks, I was stopped in gridlock traffic due to the storm over Donner Pass.
Idling was needed to keep the heater going, I'll increase the idle speed if it happens again.

I'm surprised the computer at some point didn't increase idle speed...
 
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upflying

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I did the unthinkable and brought my Ram to the dealer for a look. An extended warranty put my mind at ease regarding the cost. Stelantis apparently ordered a reflash of the PCM if a P0128 CEL appears. TSB 18-080-22 covers the latest software download. The P203F low def CEL was apparently caused by 1/3 remaining in my def tank. Refilled the DEF which required a "quick learn" of the 68RFE for some reason. All good for now, bill was no charge..
 
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