The P20E8 code means “Reductant Injection System Pressure Too Low.” Reductant is another name for DEF (AdBlue). This code says the pressure in the DEF delivery system is below what the engine computer expects, so the SCR system cannot dose enough fluid to cut NOx. It often appears alongside P20EE and P204F.

What causes low DEF pressure

• A weak or failing DEF pump.
• A clogged DEF filter or line, often from crystallized fluid.
• A stuck or leaking dosing valve (injector).
• Air in the DEF lines, or a low DEF level.
• Degraded fluid that has crystallized. See DEF quality.

How to diagnose P20E8

Check the DEF level first, then use a scan tool to command a DEF system pressure test and watch the actual pressure. Inspect the filter, lines, and injector for crystal deposits. If pressure is fine but P20EE is still present, the issue is more likely a NOx sensor or the catalyst. See NOx sensor diagnosis and our main P20EE guide.