P209E

Code

Generic P — Powertrain

Reductant Injection Air Pressure Sensor A/B Correlation

Brand: Generic

Type: P — Powertrain

Views: UK: 29 EN: 31 RU: 29

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Faulty reductant injection air pressure sensor A or B
Open, short or intermittent wiring/poor connector contact between sensors and control module
Contaminated sensor (urea/DEF crystallization) or clogged sensor port
Air supply plumbing leak, restriction or clogged filter to the reductant injector air system
Faulty reductant air pump, solenoid or air control valve affecting one side differently
ECM/DEF control module software or internal fault (less common)

Malfunction Indicator Lamp (MIL)/Check Engine illuminated
Reduced or disabled reductant dosing, possible emissions-related limp mode
Failed emissions/inspection or stored readiness/DEF-related faults
Difficulty completing active DEF dosing tests or SCR regeneration
Possible unusual injector/air pump operation noise or loss of expected pressure readings

Read and record all stored codes and freeze-frame/operating data with a scan tool
Visually inspect sensor connectors, wiring harness, and air supply plumbing for damage, corrosion, kinks or contamination
Check for secondary/related codes (DEF pump, injector, pressure control)
Monitor live data for both pressure sensors (A and B) at key conditions: key-on engine-off, idle, and under load
Listen and inspect for DEF/air system leaks; check for crystallized DEF around sensors and ports
Backprobe connectors to verify reference voltage (typically 5V), ground integrity and signal voltages

Typical sensor signal voltage range (generic): ~0.5–4.5 V (varies by manufacturer)
Reference supply: usually 5 V reference and dedicated ground — verify with service manual
Expected correlation: sensor A and B should track each other across operating range; deviation normally
At key states (KOEO, idle, increased engine load) both sensor readings should rise/fall together; sudden divergence indicates fault

Capture freeze-frame and live data for both reductant air pressure sensors; note conditions when fault set.
Verify vehicle service information for exact sensor pinouts, voltage specs and test procedures.
Perform visual inspection: unplug sensors, inspect pins for corrosion or contamination, and inspect air lines and fittings for DEF crystallization or leaks.
With ignition ON, backprobe each sensor: verify 5V reference (if used), good ground and that signal is within expected idle/KOEO range per manual.
Compare live sensor outputs side-by-side while changing engine/air demand (idle, rev, load). Confirm sensors track similarly; record differences.
Using a hand pump or calibrated pressure source (or vacuum where applicable), apply known pressure to each sensor port and confirm sensor output and linearity to the ECM.