What Does P209E Mean?
The two reductant injection air pressure sensors (A and B) are providing readings that do not correlate with each other. Both sensors should read similar pressures, and this code indicates a significant discrepancy between them.
Common Causes
40%
One of the two air pressure sensors is faulty or out of calibration
25%
Air supply line restriction or leak affecting one sensor location
15%
Sensor A or B wiring issue causing incorrect signal
12%
DEF system air distribution problem causing pressure differential
8%
Contamination or blockage at one sensor port
Diagnostic Steps
1
Step 1: Monitor live data for both sensor A and sensor B readings simultaneously during operation
2
Step 2: Compare pressure readings at idle, during DEF injection, and at various engine loads
3
Step 3: Inspect air supply lines to both sensors for restrictions, damage, or leaks
4
Step 4: Swap sensors A and B positions if possible to see if fault follows the sensor or location
5
Step 5: Test each sensor individually with known pressure source to verify accuracy
Estimated Repair Cost
$250 - $1,100
Parts + labor, varies by vehicle and location
The two reductant injection air pressure sensors (A and B) are providing readings that do not correlate with each other. Both sensors should read similar pressures, and this code indicates a significant discrepancy between them.
The most common cause of P209E (Reductant Injection Air Pressure Sensor "A"/"B" Correlation) is: One of the two air pressure sensors is faulty or out of calibration
Typical repair costs for P209E range from $250 to $1,100, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but DEF system control will be impaired. May result in increased emissions and eventual power reduction warnings.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P209E to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Emissions/SCR System
Difficulty
Type
Generic (SAE)
Recommended Tools
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