Code
P20E9
Generic
P — Powertrain
Reductant Pressure Too High
Views:
UK: 31
EN: 62
RU: 25
AI status
Completed
Completed
100%
Causes
- Blocked or kinked reductant return/overflow line
- Failed reductant pressure relief/regulated valve (stuck closed)
- Malfunctioning reductant pump (over-pressurizing)
- Faulty reductant pressure sensor or connector (incorrect reading)
- Controller/software/firmware error or calibration issue
- Contamination or crystallized reductant causing restriction
Symptoms
- Malfunction Indicator Lamp (MIL)/Check Engine light illuminated
- Reduced engine performance or limp mode in some systems
- Faults with selective catalytic reduction (SCR) dosing or failed regen events
- Visible leaks, crystallized/red/white residue around fittings or pump
- Fault codes relating to reductant system logged in ECU
What to check
- Read freeze-frame data and stored reductant-related codes from ECM and SCR controller
- Inspect reductant tank level and condition (contamination or crystallization)
- Visually inspect all reductant lines, hoses, fittings and connectors for kinks, restrictions, leaks, or residue
- Check electrical connectors and wiring to pressure sensor and pump for damage, corrosion or loose pins
- Confirm software/firmware is current and no open TSBs for reductant system
- Scan for additional codes from SCR controller or separate reductant control unit
Signal parameters
- Typical expected pressure range (system dependent): roughly 0.2–3.0 bar (3–45 psi) in normal operation — consult vehicle-specific documentation
- Pressure sensor output: expected voltage span ~0.5–4.5 V across operating range (vehicle-specific)
- Pump control: duty-cycle or PWM percent used by ECM to control pump speed
- Response behavior: pressure should rise smoothly when pump commanded and fall when relieved or pump shut off
Diagnostic algorithm
- Retrieve and record trouble codes, freeze-frame data and relevant live data (pressure, pump duty, sensor voltage)
- Visually inspect DEF tank, lines and fittings for crystallization, blockages, or leaks; clean if required
- Check wiring and connectors for continuity and proper grounding to pressure sensor and pump; repair as needed
- Using a calibrated pressure gauge or OEM diagnostic tool, measure reductant pressure while commanding pump on and while commanding relief; compare to manufacturer specs
- If pressure does not fall when relief/regulator commanded (or when pump disabled), inspect/replace pressure relief/regulator valve or associated solenoids
- If pressure gauge and sensor disagree, test/replace pressure sensor and retest
- If pump is producing excessive pressure, verify pump control signal and replace pump or control module if faulty
- Clear codes and road/test to confirm fault does not return. If intermittent, monitor for crystallization or temperature-related issues
- If problem persists, consult manufacturer service information and consider SCR module replacement or reprogramming
Likely causes
- Pressure relief/regulator valve stuck closed or stuck partially closed
- Restricted return or vent line (crystallization or debris)
- Defective pressure sensor reporting low voltage or out-of-range high pressure
- Pump control circuit driving pump at excessive duty cycle
- Recent service or replacement of pump/lines with incorrect part or installation
Fault status
Status
The reductant pressure has exceeded the expected range. The system may be over-pressurizing due to a mechanical restriction, failed regulator/relief valve, pump or sensor/electrical fault. Inspect lines and components and verify pressure with diagnostic equipment before replacing parts.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
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