P2399Diesel Intake Air Flow B Position Sensor Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2399 is the upper-limit counterpart of P2398: the B-throttle position signal reads higher than any real flap angle can produce. That usually points to a lost sensor ground, a signal wire touching the 5 V reference or battery voltage, or water bridging the terminals in the connector. No manufacturer is known to publish P2399. For the A valve the LML Duramax from GM uses P02E9 once the voltage exceeds 4.72 V during 5 s; Ford's 2023 diesels react when 4.92 V is passed for 3 s. Measure the ground lead back to the module first, since a weak ground lifts the signal without the sensor itself being damaged. The consequences resemble those of the other sensor codes: flap de-energised, MIL, EGR and regeneration compromised.
- What you may notice
- MIL on
- Flap stays at spring position
- Regeneration suspended
- Likely causes
- LikelyOpen or high-resistance sensor ground
- PossibleSignal wire shorted to 5 V reference or battery voltage
- PossibleMoisture bridging terminals in the connector
- RareFailed position sensor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.