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DylanM
Well-Known Member
I only see one other mention of that code on this site, and the cause in that one was a bad DEF pump. See below for the info from the service manual concerning this code.
P20E8-00-REDUCTANT PRESSURE TOO LOW
THEORY OF OPERATION
The Diesel Exhaust Fluid (DEF) System uses a solenoid style pump. There are two separate solenoids inside the pump, one for the pressure pump and the purge pump. The pressure pump is used to pressurize the system and deliver a supply of DEF to the DEF injector. The purge pump runs for a brief time after the vehicle has been shut down to remove DEF from the supply line. The DEF pump operates in three main stages: Pressure Build, Metering Control, and Purge. There is no pressure sensor in the system, rather pressure is a modeled calculation based off the amperage draw and the duration of the pump stroke. The higher the amperage and the longer the stroke, the higher the pressure is. Pressure seen on the scan tool is a calculation performed by the Powertrain Control Unit (PCM). cardiagn.com Once the Selective Catalyst Reduction (SCR) Catalyst reaches operating temperature of 273°F (134°C), the PCM will begin the pressure build phase. The PCM will activate the DEF Supply Pump to refill the line. As the line fills, the pressure builds to the set point. Then, the PCM turns on the DEF Injector to bleed air out of the Pressure Line. Each time the injector is turned off, the PCM monitors the amount of time it takes for the pressure to rise back to the set point to determine when all of the air is bled out of the line. During Metering Control, the PCM adjusts pump run time to maintain a steady pressure between 6.5 - 8.5 bar (94 - 123 psi). When the engine is shut off, the Purge pump will activate. The purpose is to draw the DEF back into the tank to protect the line. DEF will freeze at 12°F (-11°C) and its concurrent expansion has potential to damage the pressure line.
WHEN MONITORED
This diagnostic runs continuously when the following conditions are met: With the engine running. SCR at operating temperature. During DEF Metering control.
SET CONDITION
The DEF fluid is below 2.5 bar (36 psi) after 5 consecutive occurrences during a single drive cycle.
Possible Causes
LOW DIESEL EXHAUST FLUID LEVEL
CONTAMINATED DIESEL EXHAUST FLUID
DEF PRESSURE LINE DAMAGED/LEAKING
DEF INJECTOR PHYSICALLY STUCK OPEN
DEF PUMP SUCTION SOCKET O-RING OUT OF PLACE/DAMAGED
DEF SUPPLY PUMP ASSEMBLY
P20E8-00-REDUCTANT PRESSURE TOO LOW
THEORY OF OPERATION
The Diesel Exhaust Fluid (DEF) System uses a solenoid style pump. There are two separate solenoids inside the pump, one for the pressure pump and the purge pump. The pressure pump is used to pressurize the system and deliver a supply of DEF to the DEF injector. The purge pump runs for a brief time after the vehicle has been shut down to remove DEF from the supply line. The DEF pump operates in three main stages: Pressure Build, Metering Control, and Purge. There is no pressure sensor in the system, rather pressure is a modeled calculation based off the amperage draw and the duration of the pump stroke. The higher the amperage and the longer the stroke, the higher the pressure is. Pressure seen on the scan tool is a calculation performed by the Powertrain Control Unit (PCM). cardiagn.com Once the Selective Catalyst Reduction (SCR) Catalyst reaches operating temperature of 273°F (134°C), the PCM will begin the pressure build phase. The PCM will activate the DEF Supply Pump to refill the line. As the line fills, the pressure builds to the set point. Then, the PCM turns on the DEF Injector to bleed air out of the Pressure Line. Each time the injector is turned off, the PCM monitors the amount of time it takes for the pressure to rise back to the set point to determine when all of the air is bled out of the line. During Metering Control, the PCM adjusts pump run time to maintain a steady pressure between 6.5 - 8.5 bar (94 - 123 psi). When the engine is shut off, the Purge pump will activate. The purpose is to draw the DEF back into the tank to protect the line. DEF will freeze at 12°F (-11°C) and its concurrent expansion has potential to damage the pressure line.
WHEN MONITORED
This diagnostic runs continuously when the following conditions are met: With the engine running. SCR at operating temperature. During DEF Metering control.
SET CONDITION
The DEF fluid is below 2.5 bar (36 psi) after 5 consecutive occurrences during a single drive cycle.
Possible Causes
LOW DIESEL EXHAUST FLUID LEVEL
CONTAMINATED DIESEL EXHAUST FLUID
DEF PRESSURE LINE DAMAGED/LEAKING
DEF INJECTOR PHYSICALLY STUCK OPEN
DEF PUMP SUCTION SOCKET O-RING OUT OF PLACE/DAMAGED
DEF SUPPLY PUMP ASSEMBLY
rharr
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Top up the tank with fresh quality Def and a bottle of this, see if it fixes it.
https://a.co/d/0chA6guE
https://a.co/d/0chA6guE
mystic330
Well-Known Member
- Thread starter
- #5
Thanks for the info!
My DEF was low and I grabbed a box of no name brand from a gas station as I was traveling, and shortly after is when I got the code, so I’m kinda suspecting contamination/old fluid…. Question is how to fix now… as I’ve since filled it with known good fluid.
The code comes back pretty quickly after clearing (the setting after 5 consecutive cycles happens pretty quick!). DEF level is dropping so it is being injected… so at least it’s not in limp mode.
I think I’m gonna pull the injector first and look/clean it…. I’ll report back.
My DEF was low and I grabbed a box of no name brand from a gas station as I was traveling, and shortly after is when I got the code, so I’m kinda suspecting contamination/old fluid…. Question is how to fix now… as I’ve since filled it with known good fluid.
The code comes back pretty quickly after clearing (the setting after 5 consecutive cycles happens pretty quick!). DEF level is dropping so it is being injected… so at least it’s not in limp mode.
I think I’m gonna pull the injector first and look/clean it…. I’ll report back.
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mystic330
Well-Known Member
- Thread starter
- #6
I got the injector off...
Holy crap...!!
This is on a 3.0L with only 28k on the clock...
Cleaned it up and cleared the code.... It hasn't come back.
I definitely think this was the issue - although I would've expected a HIGH pressure issue with a clogged injector, not a low pressure code...
Getting the injector off is pretty easy - Might be worth a look if you haven't checked it before...
(if there was only a way to fix this
)
Holy crap...!!
This is on a 3.0L with only 28k on the clock...
Cleaned it up and cleared the code.... It hasn't come back.
I definitely think this was the issue - although I would've expected a HIGH pressure issue with a clogged injector, not a low pressure code...
Getting the injector off is pretty easy - Might be worth a look if you haven't checked it before...
(if there was only a way to fix this
)
'22 Ecodiesel JT
Member
Awesome, glad it wasn't a bigger issueI got the injector off...
Holy crap...!!
This is on a 3.0L with only 28k on the clock...
Cleaned it up and cleared the code.... It hasn't come back.
I definitely think this was the issue - although I would've expected a HIGH pressure issue with a clogged injector, not a low pressure code...
Getting the injector off is pretty easy - Might be worth a look if you haven't checked it before...
(if there was only a way to fix this
t-bot
Well-Known Member
I'm also glad you were able to get this resolved on your own. Without getting into a flame war, "My DEF is better than your DEF!", just curious what you typically use. Do you usually use boxed or from a station/ or combination?
That seems like an interesting problem to get at such low mileage. Did a search and the only referecne to that code was where "biodiesel' mentions getting a faild pump replaced, but that was after 113k miles link.
Regards...
That seems like an interesting problem to get at such low mileage. Did a search and the only referecne to that code was where "biodiesel' mentions getting a faild pump replaced, but that was after 113k miles link.
Regards...
mystic330
Well-Known Member
- Thread starter
- #9
I’m glad too…
I’ve usually been using boxes of DEF - name brand. I’ve heard the pump DEF is the best (truck stop) because it gets refreshed more often - but I’ve only been able to find/use that once while traveling.
it was just coincidental that this once I used a no name brand that’s probably been sitting on the shelf for a while and then have issues. But I can’t think that clog was from one box - that’s been building up for a while.
yeah I searched and found VERY little info on that code - some Cummins folks talked about it and about cleaning the injector… which lead me down that path.
I’ve usually been using boxes of DEF - name brand. I’ve heard the pump DEF is the best (truck stop) because it gets refreshed more often - but I’ve only been able to find/use that once while traveling.
it was just coincidental that this once I used a no name brand that’s probably been sitting on the shelf for a while and then have issues. But I can’t think that clog was from one box - that’s been building up for a while.
yeah I searched and found VERY little info on that code - some Cummins folks talked about it and about cleaning the injector… which lead me down that path.
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