P209C: Reductant Injection Air Pressure Sensor Circuit Low
The P209C code indicates that the reductant injection air pressure sensor circuit is reading lower than expected voltage. This sensor monitors the air pressure used to inject diesel exhaust fluid (DEF) into the exhaust stream. A low circuit condition typically points to a faulty sensor, wiring issues, or a problem with the reductant injection system. This can lead to improper DEF dosing, increased emissions, and potential triggering of the check engine light.
01. Most Common Causes
- Faulty reductant injection air pressure sensor
- Open or shorted wiring in the sensor circuit
- Poor electrical connection at the sensor connector
- Failed reductant injection pump or control module
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve the code and freeze frame data.
Step 2: Visually inspect the sensor and wiring for damage, corrosion, or loose connections.
Step 3: Test the sensor voltage and ground circuits with a multimeter; compare to manufacturer specs.
Step 4: If circuits are okay, replace the reductant injection air pressure sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause improper DEF dosing, leading to increased emissions and potential damage to the exhaust aftertreatment system. The vehicle may enter limp mode.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the vehicle and shop rates.