P20E8 – Reductant Pressure Too Low (OBD2)
P20E8 means "Reductant Pressure Too Low". The SCR system injects AdBlue (urea solution) into the exhaust to convert nitrogen oxides into nitrogen and water; these codes mean a fault in the AdBlue level, pressure, injector, heater or the system's efficiency.
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P20E8 quick summary
| Fault code | P20E8 |
|---|---|
| Meaning | Reductant Pressure Too Low |
| System | Powertrain (Engine & Transmission) |
| Vehicles | Generic OBD2 |
| Severity | High |
| Can I drive? | For a limited distance. Watch the dashboard: many vehicles count down and then limit power or prevent restarting. Top up AdBlue if it is low and have faults repaired before the countdown ends. |
| Repair cost | €0 – €2,000 |
How the SCR (AdBlue) system works
AdBlue is stored in a separate tank with a level sensor, a heater and a pump. The pump builds pressure and the dosing injector sprays AdBlue into the exhaust before the SCR catalyst. NOx sensors before and after the catalyst tell the control unit how much to inject and whether the catalyst works.
By law the vehicle must warn the driver and, if the fault is not fixed, limit the engine or prevent a restart after a countdown. Codes cover a low AdBlue level, level sensor faults, low pressure, injector circuit faults, low catalyst efficiency and NOx emissions above the limit.
Typical causes are crystallised AdBlue blocking the injector or lines, a failed pump or tank heater (often in the tank unit), poor-quality or diluted AdBlue, faulty NOx sensors and wiring faults.
Symptoms of P20E8
- AdBlue / emission warning and countdown message
- Check Engine light
- Engine will not restart after the countdown
- Reduced power
- AdBlue consumption too high or too low
Most common causes of P20E8 (most likely first)
Mechanic's Pro Tip
Never add water or anything other than ISO 22241 AdBlue to the tank. Contaminated AdBlue can destroy the pump, injector and catalyst – the repair then costs far more than a new tank of fluid.
1.AdBlue level too low or poor-quality AdBlue
Most likely2.Crystallised AdBlue in the injector or lines
White deposits block the dosing injector or pipes.
3.Failed AdBlue pump, heater or level sensor
On many vehicles these are integrated in one tank unit.
4.Faulty NOx sensor
Wrong NOx readings make the system dose wrongly and set efficiency codes.
5.Wiring or connector fault
Step-by-step diagnostic guide
- 1
Check AdBlue level and quality
Top up with ISO 22241 AdBlue if low. If contamination or dilution is suspected, check the concentration with a refractometer.
Multimeter: Correct AdBlue concentration is about 32.5 % urea.
- 2
Read codes and live data
Read all codes and check AdBlue level, pressure, temperature and both NOx sensor readings in live data.
- 3
Run the dosing and pressure tests
Use the scan tool's AdBlue pump and dosing quantity tests to check pressure build-up and the injected amount.
- 4
Inspect injector and lines
Check the dosing injector and lines for white crystals and leaks; check the tank unit connector.
- 5
Repair and reset
Clean or replace the injector, pump/tank unit or sensor, clear codes and run the SCR system adaptation; some vehicles need the countdown reset with a scan tool.
Frequently asked questions
Can I keep driving with P20E8?
For a limited distance. Watch the dashboard: many vehicles count down and then limit power or prevent restarting. Top up AdBlue if it is low and have faults repaired before the countdown ends.
How much does it cost to fix P20E8?
Typical repair costs are 0 € – 2000 €, depending on the cause and the vehicle. The most common fixes are: adBlue level too low or poor-quality AdBlue; crystallised AdBlue in the injector or lines; failed AdBlue pump, heater or level sensor. Always confirm the cause with the tests above before buying parts.
Why won't my car start after an AdBlue warning?
The law requires the engine to be disabled if an AdBlue fault is not fixed within a certain distance. Fix the fault and clear the codes; some vehicles need a scan tool to reset the countdown.
Can I just remove or disable the AdBlue system?
No. It is illegal for road vehicles, the car fails inspection and may lose its type approval.
What is the difference between P20E8 and similar codes?
P20E8 belongs to a group of codes for the same component that differ in the type or location of the fault: P203F – Reductant Level Too Low; P2047 – Reductant Injector Circuit/Open Bank 1 Unit 1; P2048 – Reductant Injector Circuit Low Bank 1 Unit 1; P2049 – Reductant Injector Circuit High Bank 1 Unit 1; P20EE – SCR NOx Catalyst Efficiency Below Threshold Bank 1; P2BAD – NOx Exceedence - Root Cause Unknown. The tests on this page apply to the whole group; the type of fault tells you where to start.
Related fault codes
- P20EESCR NOx Catalyst Efficiency Below Threshold (Bank 1)
- P2049Reductant Injector Circuit High Bank 1 Unit 1
- P2048Reductant Injector Circuit Low Bank 1 Unit 1
- P2047Reductant Injector Circuit/Open Bank 1 Unit 1
- P203FReductant Level Too Low
- P203EReductant Level Sensor Circuit Intermittent
- P203DReductant Level Sensor Circuit High
- P203CReductant Level Sensor Circuit Low
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.