P21AB CEL - Diesel Forum - TheDieselStop.com
6.7L Power Stroke Engine and Drivetrain Discussion of the 6.7L Power Stroke diesel engine and drivetrain in the 2011-Up Super Duty trucks. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.7L Power Stroke engine.

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post #1 of 10 (permalink) Old 12-20-2017, 07:52 PM Thread Starter
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P21AB CEL

Hey guys. As it is with Murphy (damn him), and my luck, I had a CEL pop up two days ago on my truck. Of course, just when I need it on a trip, and of course, one month after the extended warranty expired! Anwyay, I plugged in the ELM and connected to Forscan Lite, and it was a P21AB - Reductant Level Sensor B Circuit High. I cleared it, but it returned the next morning. I didn't drive it again until today, and it was still there. Being related to the DEF, I checked it, and it was "under 1/2 remaining". I figured I would stop and pick up some DEF and fill it, and see if it was just beyond the sensor. The dash also popped of a "800 miles remaining" message just before I got the DEF. It did take almost two full jugs. Afterward, the CEL did clear, and it seems to be fine. I checked with the dealer, and they advised against driving it. They said when it goes into regen, it will go into limp mode.

So after that sorta long sob story, what do you thing. Will it make a trip from Houston to San Antonio. I'm my pulling my 5th wheel, just me, the wife, a son, and a dog. And a back end full of presents for the other sons and grandkids. If it is something that will re-occur, I will try to replace it...I've done some sleuthing online. Dealer estimates from others with this code were around $800. Anyway, let me know. My trip is tomorrow.

Ed...KF5INW
2011 6.7L PSD XLT - Dead and gone
2019 6.7L PSD XLT - Still too new!
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post #2 of 10 (permalink) Old 12-20-2017, 08:26 PM
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Have you crawled under the truck to check if there might be any indication of bad wiring or frayed?

Is the DEF tank full?

JMHO, might be wrong, but is what I would be checking.

Larry

2015 F350 Ultra Lariat 6.7L CCLB DRW 3.73 Limited Slip, Green Gem Metallic w/ Caribou accent, Camper Package, Titan 65gal tank, Rapid Heat, Block Heater, Upfitter Switches, Dual Alternators, Camper Package, Cable Lock, Husky Floor Liners, Spray in Bedliner, 5th Wheel Prep, 25K 5th Wheel Hitch, Ford Goose Neck Hitch.

Traded 2011 F350 XLT CCLB SRW 6.2L gasser 6,000 miles for 2015

Sold 1996 F350 XLT CCLB DRW 7.3L 208,000 miles




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post #3 of 10 (permalink) Old 12-26-2017, 08:56 PM Thread Starter
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Dang Larry...I didn't even see your post. I did check the fluid level, and it was "Under 1/2 Full", according to the console reading. Shortly after that, I got the message "Less than 800 miles to empty", or whatever it said. So I stopped and got a couple of jugs of DEF. It took just short of both of them. I was going to clear the CEL code when I got home, but sometime during the drive, it cleared itself.

Now, I just got back from San Antonio, and have not had any issue. The CEL has not returned, and no issues. I can't say if it's done a regen. If it did, I missed it. Anyway, I will keep a watch on it, and try to get back and update again if anything related pops up. If it does, and it is just a sensor, hopefully I'll be able to drop the DEF tank myself and change the sensor. I'll have to google up on that to see what kind of job it may be.

Ed...KF5INW
2011 6.7L PSD XLT - Dead and gone
2019 6.7L PSD XLT - Still too new!
2010 Wildcat 28RKBS 5er
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post #4 of 10 (permalink) Old 12-27-2017, 06:53 AM
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Ed, It is not a difficult job as I understand it to replace the sensor and heater. You can pump/siphon out the DEF from the tank to make it easier. You can get a cheap pump from Wal Mart/Harbor Freight. This is part of the Ford Workshop procedure.

Larry

2015 F350 Ultra Lariat 6.7L CCLB DRW 3.73 Limited Slip, Green Gem Metallic w/ Caribou accent, Camper Package, Titan 65gal tank, Rapid Heat, Block Heater, Upfitter Switches, Dual Alternators, Camper Package, Cable Lock, Husky Floor Liners, Spray in Bedliner, 5th Wheel Prep, 25K 5th Wheel Hitch, Ford Goose Neck Hitch.

Traded 2011 F350 XLT CCLB SRW 6.2L gasser 6,000 miles for 2015

Sold 1996 F350 XLT CCLB DRW 7.3L 208,000 miles



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post #5 of 10 (permalink) Old 12-27-2017, 08:29 AM
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It has nothing to do with regen at all. The DEF level sensor B circuit has an issue. Since the level sensors and the DEF temp sensor share a common ground, the absence of codes for the other level sensors and the temperature sensor points toward the level sensor B itself. (there are three) Verifying the wiring is necessary however I am thinking there is a new DEF heater/level sensor assembly in your future. And for the record, the truck does not go into "limp mode" but rather, anything faults related to the aftertreatment system whether it be DEF related or any of the temperature sensors will trigger an engine power derate condition with had increasing degrees of severity eventually resulting in the engine being forced to idle only. Most faults result in a message center warning with a mileage range that incrementally reduces power if the fault remains. Unfortunately many truck owners ignore these warnings and end up with a truck that is undriveable or shuts down.
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post #6 of 10 (permalink) Old 12-27-2017, 10:54 AM Thread Starter
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Originally Posted by ford_doctor View Post
It has nothing to do with regen at all. The DEF level sensor B circuit has an issue. Since the level sensors and the DEF temp sensor share a common ground, the absence of codes for the other level sensors and the temperature sensor points toward the level sensor B itself. (there are three) Verifying the wiring is necessary however I am thinking there is a new DEF heater/level sensor assembly in your future. And for the record, the truck does not go into "limp mode" but rather, anything faults related to the aftertreatment system whether it be DEF related or any of the temperature sensors will trigger an engine power derate condition with had increasing degrees of severity eventually resulting in the engine being forced to idle only. Most faults result in a message center warning with a mileage range that incrementally reduces power if the fault remains. Unfortunately many truck owners ignore these warnings and end up with a truck that is undriveable or shuts down.
Thanks Larry. FordDoctor, is the replacement of this heater/sensor as straight-forward (relatively) as Larry states? I've had the heater/sensor replaced once already under warranty. I might have to dig that up and see if it was indeed the same code (and see if there is any recourse there for "re-warranty"). But for now, it is running fine, though I suspect as the DEF gets low, it may throw the code again.

Ed...KF5INW
2011 6.7L PSD XLT - Dead and gone
2019 6.7L PSD XLT - Still too new!
2010 Wildcat 28RKBS 5er
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post #7 of 10 (permalink) Old 12-27-2017, 11:02 AM
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Level sensor failures are not all that common but DEF heater failures are to some degree... same part however contains both. It's not a terribly difficult job and I suppose if you were to tackle it in the driveway at home having the tank empty would be to your advantage. Personally if I were stuck doing it that way I would simply run it low instead of messing around with pumps and such. The tank does not necessarily need to be empty to replace the part but lowering it down and putting it back up into place will be easier without the weight of 5 gallons of DEF in it. I have left them full... but I have the truck on a hoist and use a jack to lower and raise them, your preference though.


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Last edited by ford_doctor; 12-27-2017 at 11:06 AM.
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post #8 of 10 (permalink) Old 12-27-2017, 09:56 PM Thread Starter
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Good info Doc. Thanks. I would certainly have it as empty as possible. I'm getting too old to be messing with heavy stuff. I'm going to do some YouTube searching and see what I get. But for now, it is working fine, so I'll leave it be. But I still want to be prepared for when the day comes. The truck only has just short of 73K on it, and it's been a great truck. I'd like to keep it that way for a while.

Ed...KF5INW
2011 6.7L PSD XLT - Dead and gone
2019 6.7L PSD XLT - Still too new!
2010 Wildcat 28RKBS 5er
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post #9 of 10 (permalink) Old 12-29-2017, 09:58 AM Thread Starter
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Just a quick update...I had to do another road trip (Houston to Austin), and actually saw a regen start. No lights, no issues. Will update further if needed.

Ed...KF5INW
2011 6.7L PSD XLT - Dead and gone
2019 6.7L PSD XLT - Still too new!
2010 Wildcat 28RKBS 5er
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post #10 of 10 (permalink) Old 12-29-2017, 10:04 AM
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Again, this has nothing to do with a DPF regeneration.


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