Faulty reductant pressure sensor with an internal intermittent connection or failing electronics.; Damaged or corroded wiring harness or connector at the reductant pressure sensor, often due to vibration or exposure to DEF fluid.; Poor electrical connection at the PCM or an intermittent open/short in the sensor signal circuit.; Low or contaminated diesel exhaust fluid (DEF) causing pressure fluctuations that the sensor reports erratically.; A failing reductant pump or pressure regulator that produces unstable pressure, leading the sensor to read erratically.; Software issue in the PCM or reductant control module that misinterprets a valid signal as erratic.; Mechanical issue such as a restricted DEF filter or line that causes pressure pulsations.

DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P204E

P204EReductant Pressure Sensor Circuit Intermittent/Erratic

Q: What does code P204E mean?

Reductant Pressure Sensor Circuit Intermittent/Erratic. P204E indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the reductant pressure sensor, which monitors the pressure of diesel exhaust fluid (DEF) in the selective catalytic reduction (SCR) system. The PCM expects a steady, predictable voltage from this sensor, and when the signal jumps, drops out, or behaves erratically, the code is stored and the malfunction indicator lamp (MIL) is illuminated.

P204E indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the reductant pressure sensor, which monitors the pressure of diesel exhaust fluid (DEF) in the selective catalytic reduction (SCR) system. The PCM expects a steady, predictable voltage from this sensor, and when the signal jumps, drops out, or behaves erratically, the code is stored and the malfunction indicator lamp (MIL) is illuminated.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard.
Often no symptoms besides the warning light, especially if the fault is intermittent.
Reduced engine power or limp mode may be activated as a protective measure.
A message on the driver information center indicating low DEF, incorrect DEF, or a service emissions system warning.
Rough running or hesitation if the erratic signal causes incorrect DEF dosing.
Possible increase in diesel exhaust fluid consumption if the system defaults to a rich dosing strategy.

Common causes, most likely first

Faulty reductant pressure sensor with an internal intermittent connection or failing electronics.
Damaged or corroded wiring harness or connector at the reductant pressure sensor, often due to vibration or exposure to DEF fluid.
Poor electrical connection at the PCM or an intermittent open/short in the sensor signal circuit.
Low or contaminated diesel exhaust fluid (DEF) causing pressure fluctuations that the sensor reports erratically.
A failing reductant pump or pressure regulator that produces unstable pressure, leading the sensor to read erratically.
Software issue in the PCM or reductant control module that misinterprets a valid signal as erratic.
Mechanical issue such as a restricted DEF filter or line that causes pressure pulsations.

How to diagnose and fix it

Verify the stored code and check for any related codes in the reductant system using a scan tool.
Inspect the reductant pressure sensor connector and wiring for corrosion, chafing, or loose pins; repair as needed.
Check the DEF level and quality; top off or replace fluid if contaminated or diluted.
Monitor live data for reductant pressure sensor voltage while wiggling the harness and connectors to identify intermittent faults.
Perform a resistance and voltage drop test on the sensor signal and ground circuits to rule out wiring issues.
If wiring and fluid are good, replace the reductant pressure sensor with a quality part and clear the code.
After repair, run a reductant system test or drive cycle to verify the code does not return and the pressure reading is stable.

Intermittent faults often hide in the harness

A common oversight is replacing the reductant pressure sensor without first checking the wiring harness for intermittent shorts or opens, especially where it routes near hot or moving components.
The code can be set by low DEF fluid level causing aeration and pressure pulsations that the sensor interprets as erratic, so always verify fluid level and quality before condemning the sensor.
In some vehicles, a failing reductant pump can produce pressure spikes that mimic a sensor fault, so live data graphing of pressure and pump command is essential for accurate diagnosis.
This code does not always mean the sensor is defective; a poor ground connection at the chassis or engine block can cause erratic sensor readings across multiple systems.
Intermittent faults may not appear during a short test drive, so a thorough diagnosis includes wiggle tests and monitoring live data over a longer drive cycle with varying loads.

Can I keep driving with P204E?

You can generally continue driving with this code, but avoid long trips or heavy loads until it is diagnosed, because the fault may escalate to a derate or limp mode that limits vehicle speed. If the engine enters limp mode or you notice reduced power, seek service promptly.

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.