What are the common causes of P239D?

A restricted air intake or clogged filter. A stuck or restricted intake air flow B control valve. Carbon buildup in the intake air flow B passages. A failed intake air flow B control actuator.

Read the diesel intake air flow B actual air flow on a scan tool. Check the air filter and intake for a restriction. Inspect the intake air flow B valve and passages for carbon. Command the intake air flow B control and watch air flow respond. Replace the intake air flow B control actuator if it does not respond. Clear the code and retest.

P239D

Diesel Intake Air Flow B Control System - Low Air Flow Detected

System: Ignition and misfire (P code)
Lamp: Check Engine Light
Category: Powertrain - Ignition

What it means

P239D means Diesel Intake Air Flow B Control System - Low Air Flow Detected.

Check these first

A restricted air intake or clogged filter
A stuck or restricted intake air flow B control valve
Carbon buildup in the intake air flow B passages
A failed intake air flow B control actuator

What to do next

Read the diesel intake air flow B actual air flow on a scan tool
Check the air filter and intake for a restriction
Inspect the intake air flow B valve and passages for carbon
Command the intake air flow B control and watch air flow respond
Replace the intake air flow B control actuator if it does not respond
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.