Faulty reductant pressure sensor sending an erratic or out-of-range signal; Damaged or corroded wiring or connector at the sensor or powertrain control module; Clogged or restricted reductant filter or pickup screen causing low pressure; Weak or failing reductant pump unable to build or maintain pressure; Internal leakage in the reductant injector or pressure relief valve; Air intrusion into the reductant lines from a loose fitting or cracked hose; Software calibration issue in the powertrain control module requiring an update

DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P204A

P204AReductant Pressure Sensor Circuit

Q: What does code P204A mean?

Reductant Pressure Sensor Circuit. P204A indicates that the powertrain control module has detected an abnormal signal from the reductant pressure sensor, which monitors the pressure of diesel exhaust fluid in the selective catalytic reduction system. The computer compares the sensor voltage to expected values and sets this code when the signal falls outside the valid range or does not correlate with other pressure readings.

P204A indicates that the powertrain control module has detected an abnormal signal from the reductant pressure sensor, which monitors the pressure of diesel exhaust fluid in the selective catalytic reduction system. The computer compares the sensor voltage to expected values and sets this code when the signal falls outside the valid range or does not correlate with other pressure readings.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Reduced engine power or limp mode triggered by the powertrain control module
A message on the dashboard indicating low diesel exhaust fluid or a fault in the emissions system
Rough running or hesitation if the system enters a protective strategy
Increased diesel exhaust fluid consumption in some cases
Difficulty restarting the engine after shutdown if the vehicle enforces a countdown strategy

Common causes, most likely first

Faulty reductant pressure sensor sending an erratic or out-of-range signal
Damaged or corroded wiring or connector at the sensor or powertrain control module
Clogged or restricted reductant filter or pickup screen causing low pressure
Weak or failing reductant pump unable to build or maintain pressure
Internal leakage in the reductant injector or pressure relief valve
Air intrusion into the reductant lines from a loose fitting or cracked hose
Software calibration issue in the powertrain control module requiring an update

How to diagnose and fix it

Use a scan tool to read live data from the reductant pressure sensor and compare it to the commanded pressure to confirm an actual signal fault
Inspect the sensor connector and wiring for corrosion, chafing, or loose pins, and repair as needed
Check the reductant filter and pickup screen for contamination and replace if restricted
Perform a pressure test on the reductant system to verify pump output and check for leaks or air intrusion
Test the reductant pressure sensor with a multimeter or oscilloscope to confirm it responds correctly to pressure changes
Replace the reductant pressure sensor if it fails electrical or pressure response testing
Reprogram or update the powertrain control module if a known calibration issue exists, then clear codes and verify the repair

Reductant pressure sensor pitfalls to avoid

A common misdiagnosis is replacing the reductant pressure sensor when the real problem is a clogged filter or weak pump that cannot generate enough pressure for the sensor to read correctly.
The reductant pressure sensor often shares a reference voltage or ground circuit with other sensors, so a fault in a shared wire can set P204A along with codes for other sensors.
Air bubbles in the reductant lines from a loose fitting can cause pressure readings to fluctuate wildly and trigger P204A intermittently, especially after the vehicle sits overnight.
Some vehicles require a relearn or adaptation procedure after sensor replacement, and skipping this step can cause the code to return even with a new sensor.
The code can be set by a software calibration issue in the powertrain control module, so always check for technical service bulletins before replacing hardware.

Can I keep driving with P204A?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads and long trips because the powertrain control module may reduce engine power or trigger a restart countdown. If the engine enters limp mode or a countdown appears, stop driving and seek service immediately.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.