Low diesel exhaust fluid level in the tank, either from normal consumption or a leak; A weak or failing reductant pump that cannot build sufficient pressure; A clogged or restricted reductant filter or strainer; A leaking or disconnected reductant line, fitting, or injector; A faulty reductant pressure sensor sending an inaccurate low reading; Ice formation in the reductant system during freezing temperatures, blocking flow; A wiring fault or poor connection at the pump, sensor, or control module

DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20E8

P20E8Reductant Pressure Too Low

Q: What does code P20E8 mean?

Reductant Pressure Too Low. P20E8 indicates that the powertrain control module has detected reductant pressure below the expected threshold in the selective catalytic reduction system, which injects diesel exhaust fluid into the exhaust stream. The computer monitors a pressure sensor in the reductant supply circuit and sets this code when the measured pressure stays too low during commanded operation.

P20E8 indicates that the powertrain control module has detected reductant pressure below the expected threshold in the selective catalytic reduction system, which injects diesel exhaust fluid into the exhaust stream. The computer monitors a pressure sensor in the reductant supply circuit and sets this code when the measured pressure stays too low during commanded operation.

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
A message on the dashboard warning that the diesel exhaust fluid system requires service or that the vehicle will enter limp mode
Reduced engine power or a speed limitation after a certain number of restarts
Rough running or hesitation if the system enters a derate strategy
A noticeable ammonia smell or visible white crystal deposits around the injector or lines
Increased diesel exhaust fluid consumption in some cases due to the system trying to compensate

Common causes, most likely first

Low diesel exhaust fluid level in the tank, either from normal consumption or a leak
A weak or failing reductant pump that cannot build sufficient pressure
A clogged or restricted reductant filter or strainer
A leaking or disconnected reductant line, fitting, or injector
A faulty reductant pressure sensor sending an inaccurate low reading
Ice formation in the reductant system during freezing temperatures, blocking flow
A wiring fault or poor connection at the pump, sensor, or control module

How to diagnose and fix it

Check the diesel exhaust fluid level and top up with the correct specification fluid if low
Inspect the reductant tank, lines, and fittings for leaks, cracks, or loose connections
Scan live data for reductant pressure and compare commanded versus actual pressure to confirm the fault
Test the reductant pump operation and verify it can build and hold specified pressure
Replace the reductant filter or strainer if restricted, following the manufacturer's service interval
Check the pressure sensor signal and wiring for corrosion, opens, or shorts, and replace the sensor if faulty
If the pump or lines are defective, replace the failed component and clear the code, then verify repair with a road test

Reductant pressure faults that fool technicians

A low diesel exhaust fluid level is the most common cause of P20E8, yet many technicians skip the level check and go straight to replacing the pump.
The reductant pressure sensor can fail in a way that reports low pressure even when the system is mechanically sound, leading to unnecessary pump replacement.
Freezing temperatures can cause temporary low pressure codes if the reductant heater is not functioning, and the code may clear once the system thaws.
A restricted reductant injector or clogged filter can cause low pressure readings that mimic a failing pump, so always inspect the entire circuit.
Wiring harness damage near the reductant tank or pump is a common overlooked cause, especially on vehicles driven on rough roads or in corrosive environments.

Can I keep driving with P20E8?

You can usually continue driving for a short distance, but the vehicle may enter a limp mode or limit restarts once the fault is confirmed, so schedule diagnosis promptly. Avoid towing heavy loads or long trips until the reductant pressure issue is resolved, as the system may derate engine power.

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.