P203E: Reductant Level Sensor A Circuit Intermittent/Erratic

P203E stands for a level sensor A signal that keeps dropping out or jumping. FCA explains it best: Ram HD trucks with the 6.7L Cummins (2019–2021) carry an ultrasonic level sensor that needs an air gap above the fluid. Bulletin 18-034-21 and STAR case S2025000001 name an overfilled tank as the main trigger, because the echo no longer returns; residual ice or urea crystals in the focus tube after hard frost do the same. Returned parts were mostly found free of faults. The test only runs with ambient and tank above about 4 °C, so the fix is draining 2 to 3 gallons or thawing the tank, then about 15 min of steady highway driving. Jeep and Ram 3.0L EcoDiesel software updates (18-018-14, 18-018-15) also cover P203E. Steady circuit faults belong to P203C/P203D.

Symptoms

• MIL and Service DEF message
• DEF gauge jumps or reads 0 % with fluid in the tank
• Warning returns after filling or after a cold night

Most likely causes

• DEF tank overfilled, no air space for the ultrasonic echo
• Residual ice or urea crystals covering the sensor
• Intermittent contact at the tank connector
• Control unit software needing an update

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the AdBlue/DEF level and quality, and do not add additives or water
2. Gently move the wiring with the engine running and watch whether the reading changes.
3. Look for white crystals around the injector and the tank
4. Check connectors and heaters with the scanner
5. Run the dosing test available on your diagnostic tool
6. Replace parts only when the test points to that component

Good to know

• Repair difficulty: easy
• It can trigger limp mode.
• It affects emissions.

What each character of P203E means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 0: Subsystem depends on the code range
• 3E: Specific fault in that system

Frequently asked questions

Can I keep driving with code P203E?

Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

What causes code P203E?

The most common causes are: dEF tank overfilled, no air space for the ultrasonic echo; residual ice or urea crystals covering the sensor; intermittent contact at the tank connector.

Related codes

• P203AReductant Level Sensor A Circuit
• P203BReductant Level Sensor A Circuit Range/Performance
• P203FReductant Level Too Low
• P21ACReductant Level Sensor B Circuit Intermittent/Erratic
• P21B1Reductant Level Sensor C Circuit Intermittent/Erratic

Sources

• static.nhtsa.gov: MC 10194039 9999
• static.nhtsa.gov: MC 10174147 9999
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.