P2391

Code

Generic P — Powertrain

Diesel Intake Air Flow B Control Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 23 EN: 35 RU: 25

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Causes

Faulty intake air flow control valve/actuator (Carbon build-up, seized linkage, mechanical damage)
Damaged or shorted wiring / poor connector at the actuator or position sensor
Faulty intake air flow position sensor or feedback circuit (potentiometer, hall sensor)
Intake tract leaks or blockages (carbon, soot, foreign object)
Faulty related sensors (MAF, MAP, boost pressure sensor) causing incorrect PID comparison
Failed intake control module or ECM output driver

Symptoms

Malfunction Indicator Lamp (MIL) or check engine light illuminated
Reduced engine power or limp-home mode on some vehicles
Hesitation, rough idle, or surging at low load
Increased smoke or poor emissions at idle/low load
Poor fuel economy
Possible diagnostic trouble codes related to MAF, MAP, turbo boost, or EGR

What to check

Read and record DTC(s) and freeze frame data with a scan tool. Note conditions when code set (engine temp, load, RPM, boost).
Clear code and attempt to reproduce. Confirm code returns and under what conditions.
Visual inspection of intake tract, control valve/actuator, and linkage for carbon, damage, or binding.
Inspect connectors and wiring for corrosion, fraying, pin damage, or water ingress. Wiggle-test while monitoring live data.
Use a scan tool to monitor commanded vs actual valve/position values, MAF/MAP/boost sensor readings, and any related PIDs.
Check for intake vacuum/boost leaks and inspect turbocharger hoses, intercooler, and connections.

Signal parameters

Actuator command: typically 0–100% duty cycle (or 0–12 V depending on design) where 0% is closed and 100% is open
Position/feedback sensor: typically 0.5–4.5 V or 0–100% position report; should vary smoothly with commanded movement
MAF sensor: voltage or frequency proportional to airflow; should increase with engine speed/load
MAP/boost sensor: pressure should follow expected turbo response; compare commanded vs actual boost
Expected response times: actuator should reach commanded position within a few seconds under no-load bench/engine conditions
Resistance: actuator coil or motor resistance is typically low ohms for motors or higher for solenoids — consult OEM spec

Diagnostic algorithm

Retrieve all related codes and freeze frame data. Note operating conditions when the fault occurred.
Perform a thorough visual inspection of the intake air flow B valve/actuator, intake tract, and associated vacuum/boost hoses. Look for carbon, soot, restrictions, or mechanical damage.
Inspect wiring and connectors for the actuator and position sensor. Repair any damaged insulation, pins, or terminals.
With a scan tool, monitor the commanded position/duty and the actual feedback value while commanding the actuator through its range. Confirm movement and compare response times.
If actuator does not respond electrically, check supply voltage and ground at the connector with key on/engine off. Also measure resistance of actuator windings per shop manual.
If supply and control signals are correct but actuator fails, remove and bench-test or replace the actuator/valve assembly.
If actuator moves but feedback does not match command, test/replace the position sensor or recalibrate per OEM procedure.
Check related airflow sensors (MAF, MAP/boost) for plausible values; repair or replace if out of spec because incorrect inputs can trigger control-performance codes.
Inspect and clean intake passages and valves if carbon buildup is found. Re-test after cleaning.
If electrical and mechanical checks pass, consider ECM/driver faults and consult manufacturer procedures for module testing or replacement.
After repairs, clear codes and perform a road/drive cycle under the same conditions to confirm the issue is resolved.

Likely causes

Carbon/soot fouling or mechanical seizure of the intake flow control valve/runner
Wiring or connector fault to the actuator or its position sensor
Failed actuator or feedback sensor
Related sensor (MAF/MAP/boost) providing incorrect airflow data