P0420 — Catalyst System Efficiency Below Threshold — 6.7 Powerstroke

Diagnostic reference for 6.7 Powerstroke (2011–present) P0420.

Updated October 15, 2026

What it means

Catalyst efficiency, judged by downstream sensors, is below threshold.¹

Most likely causes

1. Aged or contaminated diesel oxidation catalyst — Typical on this platform: aged or contaminated diesel oxidation catalyst, or exhaust-sensor drift.¹
2. Exhaust-sensor drift¹

How to diagnose

1. Verify code and freeze-frame data; confirm P0420 is present on 6.7 Powerstroke platform.
2. Inspect aftertreatment and oxidation catalyst for signs of age/contamination per platform typicals.
3. Evaluate exhaust sensor readings for drift consistent with catalyst efficiency monitoring.

Parts and tools you may need

• OBD-II scan tool
• Exhaust gas temperature/pressure sensors
• Diesel oxidation catalyst inspection access

Tools you’ll need

• OBD-II scan tool — Reads P0420 and freeze-frame data to confirm catalyst efficiency fault on the 6.7 Powerstroke.
• digital multimeter — Checks exhaust sensor voltage and heater resistance to identify sensor drift affecting catalyst monitoring.
• exhaust gas analyzer — Measures pre- and post-catalyst emissions to verify actual diesel oxidation catalyst efficiency loss.
• inspection mirror and flashlight — Allows visual inspection of the aftertreatment and oxidation catalyst for age or contamination signs.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If catalyst replacement or sensor calibration is required, have a qualified diesel aftertreatment technician perform the work.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources