Diesel Trouble Codes

P226C — Turbocharger/Supercharger Boost Control A Position Exceeded Learning Limit (6.7 Power Stroke)

Diagnostic reference for 6.7 Powerstroke P226C.

Updated September 1, 2026

What it means

The turbo actuator’s learned travel is outside the allowable range.1

Most likely causes

  1. Sticking VGT mechanism — VGT vanes sticking from soot can cause boost control deviation and actuator learning errors.12
  2. Worn or failed turbo actuator — Actuator wear or failure can move the learned position outside the allowable range.1
  3. VGT vane sticking from soot — Soot buildup can cause VGT vane sticking, leading to boost system performance issues.2
  4. Turbo actuator calibration fault — Actuator calibration fault can cause overboost conditions and learning limit exceedance.3
  5. Boost sensor error — MAP/boost sensor error can contribute to boost control and performance faults.32
  6. Intercooler/boot leaks — Charge-air-cooler boot leaks can cause boost system performance deviation.2
  7. VGT vanes stuck closed — Vanes stuck closed can cause overboost condition.3
  8. VGT vanes stuck open — Vanes stuck open can cause underboost condition.4
  9. Sticking turbo actuator — Sticking actuator can cause underboost condition.4
  10. Restricted air filter — Restricted air filter can cause underboost condition.4

How to diagnose

  1. Verify freeze-frame data for engine speed, load, and boost at set.
  2. Command VGT actuator through scan tool and observe actual vs desired position; note if travel exceeds learned limits.
  3. Inspect VGT mechanism for sticking or soot buildup; check actuator rod movement and electrical connector.
  4. Check boost pressure readings from MAP sensor against expected values under load.
  5. Inspect charge-air system for leaks at intercooler boots and connections.
  6. Review related codes such as P0234 overboost, P2263 boost system performance, P0299 underboost for pattern correlation.

Parts and tools you may need

Rough cost and difficulty

Cost varies by root cause; actuator replacement, turbo cleaning/replacement, or sensor replacement may be required. Diagnostic time should be confirmed before repair.

When to see a pro

If VGT mechanism is seized, turbocharger requires removal and specialized service. High-pressure fuel and turbo work involve safety risks; have a qualified diesel technician perform repairs.

Sources

  1. Curated DTC seed — 6.7 Powerstroke (curated) ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — 6.7 Powerstroke (curated) ↩︎ ↩︎ ↩︎ ↩︎

  3. Curated DTC seed — 6.7 Powerstroke (curated) ↩︎ ↩︎ ↩︎

  4. Curated DTC seed — 6.7 Powerstroke (curated) ↩︎ ↩︎ ↩︎