P2038 Reductant air pressure sensor: reading or operation not right ("A")

By: Diagno editorial team · Updated: 2026-10-15

P2038 means: Reductant air pressure sensor: reading or operation not right ("A"). The AdBlue (SCR) system sprays a urea solution into the exhaust to reduce nitrogen oxides. Drive gently and have the car checked soon. The most common repair costs about €200–400 in Estonia, depending on make and model.

What it means

The AdBlue (SCR) system sprays a urea solution into the exhaust to reduce nitrogen oxides. The computer found a fault in the AdBlue quantity, quality, pump, injector or NOx sensor. There is a signal, but the reading or operation isn't plausible. The cause may be the part itself or a real mechanical fault.

What you may notice

• AdBlue warning on the dashboard
• A countdown of km left before the car won't restart
• Engine light on

What could be wrong

1. 1AdBlue low or poor quality · AdBlue injector clean or replace €200–400
2. 2AdBlue injector blocked by crystals · AdBlue injector clean or replace €200–400
3. 3Faulty AdBlue pump or heater · AdBlue injector clean or replace €200–400
4. 4Faulty NOx sensor · Sensor replacement €80–160

Repair difficulty: Moderate

What you can check yourself

Check the AdBlue level and only fill with certified AdBlue. Don't ignore the warning: eventually the car won't start. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We check AdBlue quality and quantity
2. We test the pump, injector and heater
3. We check the NOx sensors
4. We replace the faulty part

Standard SAE description: Reductant Injection Air Pressure Sensor "A" Circuit Range/Performance