A P00AF on the 6.7L Cummins indicates the turbo boost control system is not performing as expected, commonly tied to the variable-geometry turbo actuator.
What P00AF means
Turbocharger Boost Control A Module Performance is a diagnostic trouble code set when the monitored value falls outside its expected range. On the 6.7L Cummins, it narrows the problem to a specific system, and reading it correctly prevents replacing good parts.
Common causes
- Soot-stuck VGT vanes
- Failing or out-of-calibration turbo actuator
- Wiring or connector faults
- A worn VGT mechanism
Symptoms you may notice
- Limp mode and reduced power
- Weak exhaust brake
- Sluggish spool-up or excess smoke
- Boost-related codes
How to diagnose it
Read actuator commanded versus actual position and check whether the vanes move freely. Sticking vanes or a failed actuator that cannot achieve commanded boost control set this code. Inspect wiring and connectors.
How to fix it
Clean a soot-stuck VGT if the turbo is otherwise healthy, or replace and calibrate a failed actuator. Keep the emissions system healthy to limit soot loading. Verify boost control after the repair.
Frequently asked questions
What is P00AF?
A turbo boost control performance fault, usually the variable-geometry turbo actuator not achieving commanded control.
Can I clean the VGT?
If the vanes are soot-stuck and the turbo is sound, cleaning can restore function. A failed actuator needs replacement and calibration.
Does it cause limp mode?
Yes. The truck often reduces power to protect itself when boost control is compromised.
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