P221E: Reductant Heater C Current Too Low

P221E says DEF heater C pulls too little current while commanded on. Which element is C depends on the system. In GM's 2025 Duramax tables heater 3 is a second tank heater; the code needs a PWM command above zero and trips under 0.75 A after 40 readings taken every 0.1 s, a Type A fault with the MIL after one trip. GM's 2014 tables for the 6.6L LML gave the letter to the heater in the supply (pump) module instead: conductance of 0.14 S or less, checked once per trip with the battery at 11 V or more, Type B. Ford's 2023 diesel summary has a heater C only with a supply voltage check (P20C2) and does not list P221E. In frost the thawing of DEF around that heater is slow. P221F is the high-current partner, P20C1 the open control circuit.

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

Malfunction indicator lamp on
Slow DEF thawing in cold weather, dosing starts late

Most likely causes

Heater C element open or burnt (tank or supply module, by system)
Corroded or wet connector at the tank or pump unit
Heater supply missing (fuse, relay, harness)

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
With the connector unplugged, check whether the signal wire is making contact with ground.
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: hard
It can trigger limp mode.
It affects emissions.

What each character of P221E means

P: Powertrain: engine and transmission
2: Generic code: same on every make
2: Fuel injection
1E: Specific fault in that system

Frequently asked questions

Can I keep driving with code P221E?

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

What causes code P221E?

The most common causes are: heater C element open or burnt (tank or supply module, by system); corroded or wet connector at the tank or pump unit; heater supply missing (fuse, relay, harness).

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.