The P2039: Reductant Injection Air Pressure Sensor ‘A’ Circuit Low code indicates that the voltage in the reductant injection air pressure sensor circuit is lower than expected. This issue may be caused by a faulty sensor, low voltage in the circuit, or wiring and connector problems.
P2039 – Quick Overview
Code | Information |
---|---|
Meaning | P2039: Reductant Injection Air Pressure Sensor ‘A’ Circuit Low |
Is it serious? | Yes, low voltage in the air pressure sensor circuit can disrupt the proper operation of the DEF injection system, leading to poor NOx reduction and increased emissions. |
Possible causes | – Low voltage in the sensor circuit – Faulty sensor – Wiring or connector issues |
How to diagnose? | – Measure voltage in the sensor circuit – Test the sensor – Inspect wiring and connectors |
P2039 Meaning
The P2039: Reductant Injection Air Pressure Sensor ‘A’ Circuit Low code indicates that the reductant (DEF/AdBlue) injection air pressure sensor is reading a lower voltage than specified. This sensor monitors the air pressure in the system to ensure proper DEF injection. When the sensor’s voltage is too low, it can result in inaccurate pressure readings, affecting the efficiency of the emission control system.
Step-by-step diagnostic guide
Action | Description | Tools Needed |
---|---|---|
Check for Other Codes | Use an OBD-II scanner to check for any additional codes related to the reductant or emission control system. These codes may provide additional insights. | OBD-II Scanner |
Measure Voltage in the Sensor Circuit | Use a multimeter to measure the voltage in the air pressure sensor circuit for the reductant injection system. Compare the voltage readings to the manufacturer’s specifications to confirm if they are too low. | Multimeter |
Test the Air Pressure Sensor | Use a diagnostic tool or multimeter to test the air pressure sensor for proper operation. If the sensor is faulty or out of range, it may need to be replaced. | Diagnostic Tool, Multimeter |
Inspect Wiring and Connectors | Visually inspect all wiring and connectors leading to the air pressure sensor for damage, corrosion, or loose connections that may be causing low voltage in the circuit. | Flashlight, Multimeter |
Check Circuit Continuity | Perform a continuity test on the wiring connected to the sensor. Ensure there are no shorts, breaks, or high resistance that could be causing low voltage in the circuit. | Multimeter |
Inspect the Air Supply System | Check the air supply system for any blockages or restrictions that could affect the performance of the air pressure sensor. Ensure all related components are functioning properly. | Flashlight, Air Pressure Gauge |
Replace the Air Pressure Sensor | If the sensor is determined to be faulty, replace it with a new one. Ensure the new sensor is installed correctly to avoid further issues. | Replacement Air Pressure Sensor, Wrench |
Repair or Replace Damaged Wiring | Repair or replace any faulty wiring or connectors related to the sensor circuit. Ensure all electrical connections are clean and secure. | Wiring Repair Kit |
Clear the Code and Test Drive | After completing repairs, clear the P2039 code using an OBD-II scanner. Test drive the vehicle to ensure that the air pressure sensor is functioning properly and the issue is resolved. | OBD-II Scanner, Vehicle Owner’s Manual |
Recheck for Codes | After the test drive, re-scan the vehicle to verify that the P2039 code has not returned. | OBD-II Scanner |

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Hi, I am Juraj “Yuri” Lukacko. I got frustrated by unhelpful and scammy mechanics, so I decided to learn everything about car diagnostics myself. I test dozens of new car diagnostic tools every month along with learning new strategies to fix and customize cars. About Juraj Lukacko (Yuri)