OK so... I've come across a lot of references to this issue. Has anybody EVER gotten a straightforward solution?
Also, I was informed by a GMC service manager that despite being solely emissions-related, and throwing Emissions codes when there's a problem, GM classifies the DEF delivery hardware to be part of the "Fuel System", not the "Emissions System", and is therefore ONLY covered by the B2B warranty, not the Emissions system warranty.
As a foreword, I have been working 12-15 hours a day, 7 days a week since mid-december, so getting my truck to the dealership hasn't been possible until this week.
I started getting the CEL and 65mph countdown this past winter. Scanner always showed two codes; P20BE, and B20BE (permanent). Reductant heater B performance. It only ever happened when the truck sat out in temps 12°F or less (the freezing point of DEF).
Normally if the DEF lines froze overnight, the truck should upon startup examine the ambient temperature and determine that the DEF heaters need to be on. This process tells the computer to ignore the NOX readings for a little while, because obviously frozen DEF isn't going to flow. Now, the heaters SHOULD be able to thaw the system in a given (unknown) amount of time, and get things flowing.
Anyway, I would get the P20BE CEL and code a few miles into my commute. The countdown would come on and stay on. Again typically, if the computer detected that the problem had been resolved, it's supposed to cancel the countdown. If it got up into the 30° range during the day, when I would go to leave, the CEL and non-permanent P20BE would disappear upon startup. If not, it stayed, and the mileage countdown continued.
That's when I started parking inside the shop while I was at work. Once the truck was all warm and thawed out, I could start it up and the code would disappear. Didn't matter if it was -10° out, everything would work 100% a-ok on the hour long drive home with no codes.
This repeated over and over throughout the cold part of winter, until recently, when it froze up at night and thawed out during the day, the CEL went away, but the countdown didn't. Scan tool still only showed the P20BE (permanent) code. Eventually the countdown ran out and I had no choice but to get in to a shop.
This is where it gets sort of weird.
I pulled in at the dealership a few minutes before they opened, so I plugged in my scanner. There it was still, that lone P20BE (permanent). Pulled it in, explained what was going on to the service rep (who wasn't listening anyway), signed the paperwork, got my loaner and left. A few hours later they call and tell me there's absolutely nothing wrong with my truck. No explanation why the Countdown ran out, no codes whatsoever on the computer. Not even the permanent code.
Now apparently, there's a procedure called an "Emissions tamper test" that runs through and verifies the function of every single component in the system one by one. THIS TEST IS HOW THEY RESET THE COUNTDOWN AND/OR SPEED LIMITER for those of you who have been told they cannot do that. Granted, it only works if everything tests out as functional, and cannot be used to disable the speed limiter say, while you wait a week for parts to come in. But the whole "wait for a regen" or "x number of drive cycles" story is BS. If your problem has been repaired, it will pass the ETT and the countdown/limiter will go away.
Anyway, they ran an ETT and everything checked out. The test computer turned on the DEF heaters, and confirmed the proper 3 amp draw for Heater B and 8 amp draw for heater A. Anyway, everything checked out correctly. Granted, it was being worked on inside a nice warm shop, and it hasn't been cold enough for them to recreate the problem. Speed limit is gone, no codes whatsoever.
Now what I want to know is how does the PCM actually establish whether or not the heaters are functioning correctly? Does it measure the temperature of the DEF at the injector? Obviously it doesn't go by the amp load like the diagnostic computer does, since it appears to draw the correct amount of power when manually engaged.
The diagnostic computer says "heater on" and sees the proper amp draw, "confirming" that the heater works.
The PCM says "heater on", but doesn't see whatever result it's looking for and throws P20BE.
So is the heater really just not heating despite drawing exactly the right amount of current? Ohm's law says no.
Does the PCM think it's turning on the heater, but it's not? Seems unlikely, as there are separate fault codes for no voltage, low current, and excessive current. (P20BD, P20BF, and P20C0)
Is the heater really heating and the PCM isn't detecting it? Again, that would mean the PCM goes by temperature at the nozzle, not by an electrical anomaly.
Is the heater heating and it's just a shitty design that isn't sufficient to thaw a frozen line?
I'm banging my head against the desk here. At least they're only charging me for diagnostics, and not just throwing parts at it and sending me a bill. I doubt we'll have any more cold enough temps this year to do any further diagnostics on it, but that also means I've got 9 months of (hopefully) trouble-free driving ahead of me before I need to worry about it again.
Also, I was informed by a GMC service manager that despite being solely emissions-related, and throwing Emissions codes when there's a problem, GM classifies the DEF delivery hardware to be part of the "Fuel System", not the "Emissions System", and is therefore ONLY covered by the B2B warranty, not the Emissions system warranty.
As a foreword, I have been working 12-15 hours a day, 7 days a week since mid-december, so getting my truck to the dealership hasn't been possible until this week.
I started getting the CEL and 65mph countdown this past winter. Scanner always showed two codes; P20BE, and B20BE (permanent). Reductant heater B performance. It only ever happened when the truck sat out in temps 12°F or less (the freezing point of DEF).
Normally if the DEF lines froze overnight, the truck should upon startup examine the ambient temperature and determine that the DEF heaters need to be on. This process tells the computer to ignore the NOX readings for a little while, because obviously frozen DEF isn't going to flow. Now, the heaters SHOULD be able to thaw the system in a given (unknown) amount of time, and get things flowing.
Anyway, I would get the P20BE CEL and code a few miles into my commute. The countdown would come on and stay on. Again typically, if the computer detected that the problem had been resolved, it's supposed to cancel the countdown. If it got up into the 30° range during the day, when I would go to leave, the CEL and non-permanent P20BE would disappear upon startup. If not, it stayed, and the mileage countdown continued.
That's when I started parking inside the shop while I was at work. Once the truck was all warm and thawed out, I could start it up and the code would disappear. Didn't matter if it was -10° out, everything would work 100% a-ok on the hour long drive home with no codes.
This repeated over and over throughout the cold part of winter, until recently, when it froze up at night and thawed out during the day, the CEL went away, but the countdown didn't. Scan tool still only showed the P20BE (permanent) code. Eventually the countdown ran out and I had no choice but to get in to a shop.
This is where it gets sort of weird.
I pulled in at the dealership a few minutes before they opened, so I plugged in my scanner. There it was still, that lone P20BE (permanent). Pulled it in, explained what was going on to the service rep (who wasn't listening anyway), signed the paperwork, got my loaner and left. A few hours later they call and tell me there's absolutely nothing wrong with my truck. No explanation why the Countdown ran out, no codes whatsoever on the computer. Not even the permanent code.
Now apparently, there's a procedure called an "Emissions tamper test" that runs through and verifies the function of every single component in the system one by one. THIS TEST IS HOW THEY RESET THE COUNTDOWN AND/OR SPEED LIMITER for those of you who have been told they cannot do that. Granted, it only works if everything tests out as functional, and cannot be used to disable the speed limiter say, while you wait a week for parts to come in. But the whole "wait for a regen" or "x number of drive cycles" story is BS. If your problem has been repaired, it will pass the ETT and the countdown/limiter will go away.
Anyway, they ran an ETT and everything checked out. The test computer turned on the DEF heaters, and confirmed the proper 3 amp draw for Heater B and 8 amp draw for heater A. Anyway, everything checked out correctly. Granted, it was being worked on inside a nice warm shop, and it hasn't been cold enough for them to recreate the problem. Speed limit is gone, no codes whatsoever.
Now what I want to know is how does the PCM actually establish whether or not the heaters are functioning correctly? Does it measure the temperature of the DEF at the injector? Obviously it doesn't go by the amp load like the diagnostic computer does, since it appears to draw the correct amount of power when manually engaged.
The diagnostic computer says "heater on" and sees the proper amp draw, "confirming" that the heater works.
The PCM says "heater on", but doesn't see whatever result it's looking for and throws P20BE.
So is the heater really just not heating despite drawing exactly the right amount of current? Ohm's law says no.
Does the PCM think it's turning on the heater, but it's not? Seems unlikely, as there are separate fault codes for no voltage, low current, and excessive current. (P20BD, P20BF, and P20C0)
Is the heater really heating and the PCM isn't detecting it? Again, that would mean the PCM goes by temperature at the nozzle, not by an electrical anomaly.
Is the heater heating and it's just a shitty design that isn't sufficient to thaw a frozen line?
I'm banging my head against the desk here. At least they're only charging me for diagnostics, and not just throwing parts at it and sending me a bill. I doubt we'll have any more cold enough temps this year to do any further diagnostics on it, but that also means I've got 9 months of (hopefully) trouble-free driving ahead of me before I need to worry about it again.
