P221FReductant Heater C Current Too High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P221F flags excessive current through DEF heater C, pointing to a partial short in the element or its lead. GM's 2025 Duramax tables, where heater 3 is the second tank heater, set the code above 15 A over 40 samples of 0.1 s whenever the vehicle is active, Type A with the MIL after one trip, and zero all heater PWM commands while any heater fault is present. In GM's 2014 tables for the 6.6L LML, C denoted the supply module heater, and high conductance (0.46 S or more in one table, 0.35 S in the other) set a Type B fault once per trip. Ford's 2023 diesel summary does not use P221F. A shorted heater draws more than its driver tolerates, so the area it serves stays unheated. P221E is the low-current partner.
- What you may notice
- Malfunction indicator lamp on after one trip (GM)
- DEF heating disabled, possible frozen-DEF warnings in winter
- Likely causes
- LikelyPartly shorted heater C element
- PossibleHeater lead chafed to ground at the tank or pump unit
- RareWater or DEF crystals in the heater connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.