What P13DF and P20E8 Mean

The P13DF fault relates to the AdBlue tank heater circuit — it prevents the fluid from freezing during cold weather. When resistance in the heater element or wiring is too high, the ECU detects a malfunction.

The P20E8 fault means low reductant pressure in the SCR pump line. This can be caused by air leaks, blockage, or a weak pump motor. In most cases, one triggers the other: when the fluid can’t warm up, pressure drops, and both codes appear together.

Models Commonly Affected

We see this fault combination on Sprinter 906/907, Vito 447, and C-Class OM651/OM654 diesels. They share the same modular SCR system used across Mercedes cars and vans from 2014 onward.

Typical Symptoms

• “AdBlue System Fault” message or orange warning light
• Stored codes P13DF00 and P20E800
• Countdown: “No Start in XXX miles”
• Longer cold starts and increased AdBlue use
• Fan running longer after shutdown

Root Causes of P13DF

• Failed tank or line heater element
• Corroded connector near the AdBlue pump assembly
• Internal short or open circuit in heater wiring
• ECU misread due to low battery voltage in cold weather

Root Causes of P20E8

• Blocked dosing injector or crystal build-up
• Air trapped after tank refill
• Weak or damaged SCR pump
• Frozen fluid preventing flow from the tank

How the Two Faults Interact

When the heater fails (P13DF), the system can’t thaw the AdBlue, causing the pump to run dry. The ECU then detects low line pressure and logs P20E8. In other cases, low pressure itself makes the ECU believe the heater has failed, so both appear even though only one component is bad.

How to Test the Heater Circuit

With a diagnostic tool, monitor current draw for the tank heater. It should read around 3–4 A. Zero current means an open circuit; above 6 A indicates a short. Resistance testing at the connector can confirm whether the fault lies in the heater or the harness.

Live Pressure Checks for P20E8

Live data will show target pressure (usually 5000 kPa) versus actual. Anything under 2500 kPa during dosing attempts confirms a pressure issue. If the pump motor runs but pressure stays low, inspect for leaks or crystallisation in the injector line.

How We Fix P13DF and P20E8

Our mobile AdBlue repair service performs full SCR diagnostics at your location. We test heater resistance, pump output, and ECU signals before applying software resets or safe AdBlue deletes for off-road/export vehicles.

In many cases, we restore proper dosing without replacing any hardware. When parts are required, we fit OEM components and reprogram the control module for accurate pressure calibration.

Other Related Codes

• P3041 – Heated Pipe & DEF Quality Fault
• SPN 4354 – DEF Line Heater 1 Fault
• P207F vs P20EE – Quality vs Efficiency Fault

Example Case: Sprinter OM651

A 2018 Sprinter 2.1 CDI logged P13DF00 and P20E800 after sitting unused for a week in freezing weather. Live data showed 0 A heater current and 1900 kPa line pressure. The heater circuit tested open at 29 Ω — a clear failure. After fitting a new heater and running an SCR pressure bleed, both faults cleared and dosing resumed normally.

How to Prevent It

• Keep AdBlue above ¼ tank in winter — less air space means less freezing risk.
• Start the van weekly during cold months to circulate heated fluid.
• Avoid jet-washing around the AdBlue tank and pump area.
• Have the SCR system checked yearly before winter.

Can You Keep Driving?

Yes, temporarily, if temperatures are mild. But once it freezes overnight, pressure will drop and the countdown will begin. Once it reaches zero, the engine won’t restart until both faults are cleared. Getting it repaired early avoids downtime.

Our Coverage Area

We provide mobile AdBlue repair in Stoke-on-Trent, Stafford, Crewe, and Newcastle-under-Lyme. Same-day visits available for most Mercedes Sprinter and Vito models.

Why Choose AdBlue Specialist

• 250 + AdBlue jobs since 2021
• IMI-registered, fully insured technicians
• Dealer-level diagnostics — Autotuner & CMD Flash tools
• No towing, no workshop visit, safe ECU software fixes

Need Help With P13DF or P20E8?

If your Mercedes shows P13DF or P20E8, we can identify the cause and clear the countdown quickly. Don’t wait for a non-start — get it fixed today.