Powertrain, generic (extended)

P221E Reductant Heater C Current Too Low

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modePossible

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.

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)

Symptoms

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

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,800

Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant line heater c

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.