P203D: Reductant Level Sensor A Circuit High

P203D is the high-side fault of level sensor A. On the LML Duramax and the 2014 Cruze 2.0D, GM samples level contact 1 1.5 ms after a test pulse: 3.56 to 4.74 V means an open load, above 4.74 V a short to battery, either one for more than 3 s with Type A. GM's 2017 diesel table uses a raw value above 95 (Type B), while the 2025 DEF controller sets P203D when the ultrasonic sensor reports a level beyond its 400 mm measuring range for 6 s. Preliminary bulletin PIP4887B for 2010–2011 Duramax trucks names P203D with P21AB and P21B0 and asks for wiring and terminal checks even on history codes before a new DEF tank. FCA (Ram 6.7L, 2014–2015) and Jaguar (2.0D, overfilled tank reading zero) list P203D as well. Low-side faults are P203C.

Symptoms

• MIL with Service Exhaust Fluid System or similar message
• DEF gauge missing or showing full permanently
• Speed or restart limit if not repaired

Most likely causes

• Open circuit, unplugged or loose tank connector
• Signal wire shorted to supply or battery voltage
• Overfilled tank on ultrasonic sensors
• Failed level sensor or tank assembly

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. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
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: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P203D means

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

Frequently asked questions

Can I keep driving with code P203D?

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

What causes code P203D?

The most common causes are: open circuit, unplugged or loose tank connector; signal wire shorted to supply or battery voltage; overfilled tank on ultrasonic sensors.

Related codes

• P203AReductant Level Sensor A Circuit
• P203CReductant Level Sensor A Circuit Low
• P203BReductant Level Sensor A Circuit Range/Performance
• P21ABReductant Level Sensor B Circuit High
• P21B0Reductant Level Sensor C Circuit High

Sources

• gsi.ext.gm.com: 14OBDG10 Engine Diagnostics
• static.nhtsa.gov: MC 10112047 9999
• gsi.ext.gm.com: 25OBDG04A
• static.nhtsa.gov: MC 10148941 9999

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.