Seeing P20E8 on your dash or scan tool? That code means the AdBlue (DEF) system can’t build enough pressure. Below we explain what causes low pressure, how we diagnose it on your drive, and the quickest way to fix it.
What P20E8 actually means
P20E8 is “Reductant Pressure Too Low.” In plain English: the SCR system isn’t getting the AdBlue pressure it expects, so dosing is cut back and warnings trigger. Leave it, and you can get limp mode or a no-start countdown.
Good to know: Low pressure can be the pump, blocked lines, a sticking pressure relief valve, a clogged filter, or wiring/voltage drop to the pump module.
Typical symptoms you’ll notice
- P20E8 fault stored and AdBlue warning light on.
- “0 miles until no start” style countdown appearing after a few key cycles.
- Reduced power or SCR/engine management warning.
- Fan running after shutdown while the module tries to prime.
Main causes of low AdBlue pressure
- Pump wear or failure: The internal gear pump can’t build target pressure at prime.
- Clogged pickup or filter: Crystal build-up or contaminated fluid restricts flow.
- Frozen or gelled fluid: After severe cold, ice can block the pickup or lines until the heater wakes up.
- Leaking line or injector: Pressure drops under demand; you may smell ammonia near the rear of the van.
- Electrical issues: Poor ground, low battery, corroded connector, or failed pressure sensor feedback.
Our on-site diagnostic process
We come to you and run a structured test so you’re not guessing at parts. Here’s the short version:
- Initial scan & freeze-frame: Confirm P20E8 and check related codes like P204F (system performance) or NOx sensor faults.
- Prime & pressure test: Command the pump to prime and watch target vs actual pressure and time-to-pressure.
- Electrical checks: Battery state, live voltage at the pump, grounds, and connector condition.
- Flow & restriction check: Inspect lines, filter screen, and injector for blockages or leaks.
- Heater status (cold weather): Verify the tank/line heater switches in and the temp sensor reads sensibly.
- Road test & verify: Clear codes, trigger dosing events, and confirm stable pressure under load.
If the fault sits alongside NOx codes, read this next: Signs of NOx sensor failure and NOx sensor delete vs replacement.
Fix options we offer on your driveway
- Software resets & adaptations: After the hardware is healthy, we reset the AdBlue counter and run guided priming. See: AdBlue fault codes: reset options.
- Wiring & connector repairs: Corrosion at the tank module plug is common; we test and put it right.
- Pump/line/injector remedies: Where the pump can’t hold pressure, we advise on the most sensible repair route.
- Emergency countdown clear: Need it gone today? Read how to clear a no-start countdown without the dealer.
DIY checks before we arrive
- Confirm you’re using genuine, fresh AdBlue (ISO 22241). Contamination or mixed fluids cause repeat faults.
- Check battery health; low cranking voltage can trigger pressure faults.
- Look under the van for any damp AdBlue residue along the lines or at the injector.
Will P20E8 come back after clearing?
If the root cause stays—yes. A quick clear can silence the dash for a day, then the pressure test fails and the warning returns. That’s why we pair a reset with proper testing. If your van repeatedly throws AdBlue warnings, read why systems keep failing again and again.
Related faults you might see with P20E8
- P204F: Reductant system performance (often appears with low pressure).
- P207F: Reductant quality issues after contamination or old fluid.
- P20EE: SCR catalyst efficiency; sometimes triggered by poor dosing history.
When repair isn’t the right answer
Some fleets choose a software-only path to avoid repeat AdBlue spend. If you’re weighing choices, start with AdBlue delete vs repair — what’s right? and Is AdBlue delete legal in the UK?
Book a mobile diagnostic today
We fix P20E8 at your home or workplace—no tow, no dealer wait. Most visits take under an hour once we’re on site. See what a full diagnostic includes or book a mobile visit.
Helpful links
- SCR system repair (mobile)
- AdBlue delete service
- Delete vs repair (updated guide)
- AdBlue fault codes: reset options
- Latest AdBlue guides
Need the P20E8 warning gone before MOT?
Call 07349 821 999 or email info@ifixadblue.co.uk. Mobile visits across Leicestershire and nearby counties.
