P21AB CEL
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Cargo Master
Joined: Jan 2007
Posts: 2,243
Likes: 79
From: Roman Forest, TX
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.
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.
Elder User
Joined: Jul 2006
Posts: 585
Likes: 4
I just went through the same thing. CEL, Filled the DEF tank, and cleared the code. Drove 2000 miles, pulling my big fiver with no issues. A few days later, CEL. Tried to put more DEF in and it wouldn't take it.
Took it to a dealer and they dropped the DEF tank and replaced the heater/sensor unit. I asked why it wouldn't take more DEF and he said the tank was full.
So it appears that I drove 2000 miles, pulling heavy, and didn't use a drop of DEF.
Another thing: What does DEF have to do with regen? Two different systems. Regens use extra fuel, not DEF. The mechanic tried to make the same argument with me, but couldn't explain why when I asked.
From all the gripes about this particular problem with the DEF system, it is starting to look like Ford didn't get it quite right
Took it to a dealer and they dropped the DEF tank and replaced the heater/sensor unit. I asked why it wouldn't take more DEF and he said the tank was full.
So it appears that I drove 2000 miles, pulling heavy, and didn't use a drop of DEF.
Another thing: What does DEF have to do with regen? Two different systems. Regens use extra fuel, not DEF. The mechanic tried to make the same argument with me, but couldn't explain why when I asked.
From all the gripes about this particular problem with the DEF system, it is starting to look like Ford didn't get it quite right
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Cargo Master
Joined: Jan 2007
Posts: 2,243
Likes: 79
From: Roman Forest, TX
Hi all. Update time. First, to attempt an answer to glsurratt, DEF doesn't have anything to do with the regeneration, but rather burns the junk the regen makes prior to shooting it out the exhaust...I think. Something similar.
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.
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.
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