P20E8 — Reductant Pressure Too Low (6.7 Power Stroke)

Diagnostic reference for P20E8 on 6.7 Powerstroke.

Updated September 1, 2026

What it means

DEF (reductant) delivery pressure is below target.¹

Most likely causes

1. DEF pump performance / failure — Typical on this platform: DEF pump.¹
2. Frozen or clogged DEF line / filter — Typical on this platform: a frozen or clogged DEF line/filter.¹
3. Dosing valve restriction / fault — Typical on this platform: the dosing valve.¹

How to diagnose

1. Verify freeze conditions and DEF quality; frozen DEF can cause low reductant pressure.
2. Inspect DEF supply line and filter for blockage or ice; typical cause per platform.
3. Check reductant pump operation and pressure feedback; pump is a typical cause.
4. Evaluate dosing valve for restriction or malfunction; listed as typical.

Parts and tools you may need

• Scan tool with live reductant pressure data
• DEF line inspection kit
• DEF filter
• DEF pump
• Dosing valve

Rough cost and difficulty

Parts and labor vary by vehicle and shop; obtain a quote before work.

When to see a pro

High-pressure fuel and emissions systems require trained service. If the vehicle derates or shows additional SCR/DEF faults, have a qualified diesel technician diagnose and repair.

Sources

Watch a repair

Third-party videos, not ours — for illustration. Confirm anything against the factory service information for your truck.

P20E8 DEF Pressure too low 6.7 powerstroke — FullmetalToolBox