P20E8: How to Diagnose & Fix — Reductant Pressure Too Low
7 vehicles · 7 makes · $150-$2,500 repair
How to diagnose and fix P20E8: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Volkswagen Touareg · 2011–2022
North American 3.0 TDI Touaregs (2011-2016, engine codes CATA/CNRB) and Euro 6 diesel Touaregs use an SCR system that injects AdBlue (DEF) to reduce NOx. Faults in this system — a failed NOx sensor, blocked AdBlue injector, failed AdBlue tank heater, or AdBlue crystallization/poor-quality fluid — trigger a dash warning and a legally-mandated no-start countdown ('No start possible in XXX km/starts'). Once the countdown reaches zero and the ignition is cycled, the vehicle will not restart, stranding the owner. In Europe, SCR arrived with the Euro 6 facelift, and VW of America publishes an SCR (AdBlue) light reset procedure for the US 2011-2016 3.0 TDI. Common diagnostic faults include 'NOx Reductant Consumption too Low', 'Reductant Quality Performance', and NOx sensor signal-low codes.
Common Symptoms
- 'AdBlue fault' / 'No start possible in X km' warning on dash
- Emissions warning light
- Reduced power / limp mode
- Vehicle refuses to start after countdown expires
How to Fix
Diagnose with VCDS/dealer tool. Fixes depend on cause: replace the faulty NOx sensor, clean or replace a blocked AdBlue injector, replace the AdBlue tank heater, or refill with quality DEF and clear crystallization. The SCR no-start counter usually must be reset by a dealer/specialist after the repair.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (4)
Jeep Grand Cherokee · 2014–2016
A DEF/SCR warning or reductant-system DTC on a 2014-2016 Grand Cherokee EcoDiesel does not prove that the complete DEF tank has failed. FCA documentation shows materially different causes and remedies within this model range: one defined 2015 population received PCM software and a fluid-level reset for reductant codes, while a separate, narrowly defined 2015 VIN/build population with manufacturing contamination required several DEF/SCR components. Eligible vehicles that received the Approved Emissions Modification may also have extended-warranty coverage for multiple DEF-system parts and diagnostic scanning.
Common Symptoms
- Malfunction indicator lamp
- Service DEF or reductant-system warning
- A stored DEF/SCR pressure, heater, quality, or system-performance DTC
How to Fix
Record the exact DTCs, freeze-frame data, warning text, VIN, build date, and current PCM software level. Have an EcoDiesel-capable shop or Jeep dealer follow the code-specific FCA diagnostic procedure and check whether a VIN-specific service action, applicable software update, or AEM extended warranty applies. Do not infer a failed tank from P20E8, P204F, P20EE, or another reductant code alone: verify the relevant pressure, heater, level/temperature input, fluid quality/contamination, delivery line, injector, SCR catalyst, wiring, and control-software path specified for that VIN. Replace only the component the tests and applicable FCA procedure identify.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Owner tips & cautions
- TipBring the exact code, freeze-frame data, VIN, build date, and software level to diagnosis; FCA's documented remedy changes with those details.
- WarningDo not buy a complete DEF tank from the warning message alone. FCA records show that software, contamination, the tank, lines, injector, catalyst, pump, sensors, or related controls can require different service paths.
- TipFor a 2014-2016 EcoDiesel that received the Approved Emissions Modification, check the transferable extended-warranty term before paying for DEF/SCR diagnosis or covered parts.
Sources for this issue (3)
Mercedes-Benz GLA · 2015–2023
GLA diesels (GLA 200d/220d), popular in Germany and the EU, develop clogged EGR valves and diesel particulate filters from soot buildup, plus AdBlue/SCR (NOx reduction) faults. EGR carbon fouling causes rough idle, reduced power and emissions faults; DPF blockage triggers limp mode if regeneration can't complete (common with short urban trips). AdBlue/SCR issues include crystallization from irregular use, sensor/NOx-sensor faults, level/quality warnings and countdown-to-no-start messages. The OM651 also shares timing-chain-stretch tendencies.
Common Symptoms
- Limp mode / reduced power
- Check engine and DPF warning lights
- AdBlue level/quality warning with no-start countdown
- Rough idle
- Excessive smoke
- Increased fuel consumption
How to Fix
Carry out periodic motorway runs to allow active DPF regeneration; clean or replace a clogged EGR valve and clear/replace a blocked DPF. SCR faults require diagnosing and replacing NOx sensors, the SCR/AdBlue metering/dosing unit, or clearing crystallization, then resetting the no-start countdown via XENTRY. Use only fresh, correct-spec AdBlue and keep the tank topped.
Sources for this issue (2)
Mazda CX-60 · 2022–2025
Peugeot 208 · 2015–2023
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P20E8 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P20E8 mean?
P20E8 stands for "Reductant Pressure Too Low." P20E8 is a generic powertrain code that applies to diesel vehicles with a Selective Catalytic Reduction (SCR) emissions system, which injects diesel exhaust fluid (DEF, also sold as AdBlue) into the exhaust to convert smog-forming nitrogen oxides into harmless nitrogen and water. The engine control module sets this code when the DEF pump cannot build or hold the pressure the system needs (roughly 70-90 psi on most applications) to dose fluid accurately into the exhaust stream. Day to day you may notice little beyond a check engine light and a DEF or SCR warning message, though some vehicles show reduced power. Because SCR operation is emissions-mandated, ignoring the code typically starts a countdown to a derate: the vehicle will progressively limit speed (often to 55 mph, then as low as 5 mph on trucks) or refuse to restart until the fault is repaired. Some manufacturers word the same code as "DEF Pressure Too Low" or "SCR Urea Pressure Too Low," but the meaning is identical.
What are the most common causes of P20E8?
The most common causes of P20E8 are: Failed or weak DEF (reductant) pump that cannot build specified pressure, Clogged reductant pump filter cartridge — DEF crystals gumming the internal filter is the most common cause on Duramax and Power Stroke trucks, Contaminated, diluted, or crystallized DEF fluid (or DEF frozen in cold weather due to a failed heater), Leaking DEF supply lines or fittings, or a DEF injector stuck open and bleeding off pressure, Faulty reductant pressure sensor giving a false low reading, Damaged or corroded wiring/connectors to the DEF pump or pressure sensor, Low DEF tank level. The specific cause varies by vehicle.
How much does it cost to fix P20E8?
Repair costs for P20E8 range from $150 to $2,500, depending on the vehicle and root cause.
Which vehicles are affected by P20E8?
Au7o has documented P20E8 across 7 vehicle models from 7 manufacturers: Jeep, Mazda, Mercedes-Benz, Opel, Peugeot, Skoda, Volkswagen.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.