P2040

Reductant Injection Air Pressure Sensor A Circuit High

Q: Is it safe to drive with P2040?

Short-term yes, but diesel emissions systems often respond to reductant faults with a power derate or a limited-restart countdown. Repair it promptly to avoid being limited.

Q: Can I just clear P2040?

It will return until the sensor or circuit fault is fixed. This is an electrical range fault, not a temporary glitch.

Auxiliary emissions (SCR/diesel exhaust fluid) Generic OBD-II Medium

What it means

P2040 means the PCM sees a higher-than-expected voltage from reductant injection air pressure sensor A — part of the SCR (diesel exhaust fluid) after-treatment system that meters air-assisted reductant into the exhaust. It's usually a sensor, wiring, or connector fault, and while the engine still runs, diesel emissions systems may respond with a power derate if it isn't repaired.

Medium

Can I keep driving? Driveable at first, but the emissions system may trigger a power derate or countdown — repair before it limits performance.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on
Reduced engine power or a derate warning (on diesels)
Reductant/DEF system warning message

Common causes

Most likely first

Faulty reductant injection air pressure sensor ALikely
Wiring shorted to voltage or open in the sensor circuitCommon
Corroded or loose sensor connectorCommon
Air-assist/reductant pressure delivery problemLess often
Faulty powertrain control module (PCM)Less often

How to diagnose & fix

Work through it in order

Read freeze-frame data and inspect the sensor wiring and connector for shorts-to-power, opens, or corrosion.
Compare the sensor's live pressure reading to the air-assist system's actual pressure.
Replace the reductant air pressure sensor A if it reads out of range with good wiring.
If pressure is genuinely off, inspect the air pump/delivery side; consider the PCM last.

FAQ

Quick answers

Is it safe to drive with P2040?+

Short-term yes, but diesel emissions systems often respond to reductant faults with a power derate or a limited-restart countdown. Repair it promptly to avoid being limited.

Can I just clear P2040?+

It will return until the sensor or circuit fault is fixed. This is an electrical range fault, not a temporary glitch.

Read & clear P2040 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX