P204D: Reductant Pressure Sensor Circuit High

P204D is the high-side counterpart: the pressure signal sits near or above the supply voltage, typically because the signal wire touches 5 V or battery voltage, the sensor ground is open, or the sensor has failed internally. Published limits are 4.80 V on GM's 6.6 L LML, 98 % of the supply in GM's 2018 diesel table, 4.90 V in GM's 2025 DEF controller and 4.85 V on Ford's 2023 diesels. GM's 2014 Cruze diesel logs it as Type B, the other GM tables as Type A. Deutz's EMR L1 calls the same state a short circuit to battery. To the controller such a reading could look like over-pressure, which is why it stops the pump; check the connector at the pump module and the sensor ground before replacing the module.

Medium severity. Can I keep driving?Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

Symptoms

MIL on (after two trips on some GM diesels)
DEF pump stopped, no dosing
DEF warning and later inducement

Most likely causes

Open sensor ground or corroded ground terminal
Signal wire shorted to 5 V reference or battery voltage
Internal failure of the pressure sensor in the pump module

What to check, in order

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

Check the AdBlue/DEF level and quality, and do not add additives or water
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Look for white crystals around the injector and the tank
Check connectors and heaters with the scanner
Run the dosing test available on your diagnostic tool
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 P204D means

P: Powertrain: engine and transmission
2: Generic code: same on every make
0: Subsystem depends on the code range
4D: Specific fault in that system

Frequently asked questions

Can I keep driving with code P204D?

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

What causes code P204D?

The most common causes are: open sensor ground or corroded ground terminal; signal wire shorted to 5 V reference or battery voltage; internal failure of the pressure sensor in the pump module.

Related codes

Sources

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.