P2037: Reductant Injection Air Pressure Sensor A Circuit

Some heavy-duty SCR systems do not spray DEF on their own pressure alone but blow it into the exhaust with compressed air, supplied by a compressor or an existing air system; Bosch's first Denoxtronic generation was built this way. A pressure sensor checks that this air is present before dosing. P2037 is the general circuit fault of that sensor. Deutz uses it on the EMR L1 controller (SPN 4335) for two failure types: a ground fault (-F0) and a sensor supply out of range (-1C), while a reading stuck low or open goes to P2039 and a short to battery to P2040. CARB names air assisted injection as part of the reductant delivery that must be monitored. With the air pressure unknown, dosing is normally stopped, and on trucks a power derate may follow.

Symptoms

• Engine or emission warning lamp on
• DEF dosing suspended
• Engine power derate on trucks and machines

Most likely causes

• 5 V supply or ground of the sensor interrupted or shorted
• Damaged harness or corroded connector at the dosing module
• Air pressure sensor failed internally

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the AdBlue/DEF level and quality, and do not add additives or water
2. Look for white crystals around the injector and the tank
3. Check connectors and heaters with the scanner
4. Run the dosing test available on your diagnostic tool
5. Replace parts only when the test points to that component

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P2037 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 0: Subsystem depends on the code range
• 37: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2037?

Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

What causes code P2037?

The most common causes are: 5 V supply or ground of the sensor interrupted or shorted; damaged harness or corroded connector at the dosing module; air pressure sensor failed internally.

Related codes

• P2038Reductant Injection Air Pressure Sensor A Circuit Range/Performance
• P2039Reductant Injection Air Pressure Sensor A Circuit Low
• P2040Reductant Injection Air Pressure Sensor A Circuit High
• P2041Reductant Injection Air Pressure Sensor A Circuit Intermittent
• P209AReductant Injection Air Pressure Sensor B Circuit
• P2059Reductant Injection Air Pump Control Circuit/Open

Sources

• serdia.deutz.com: DTCList EMRL1 MainECU EN
• energy.gov: 2005 deer hesser
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.