P221DReductant Heater B 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
- P221D is stored when heater B, the electrically heated DEF pressure line at GM and Ford, takes more current or power than its design permits. That usually means a partly shorted element or a lead touching ground, and the controller cuts the heater to save its driver. GM's 2025 Duramax tables trip above 15 A, counted over 40 samples of 0.1 s while the vehicle is active, Type A with the MIL on the first trip and recovery only in the next drive cycle. Ford's 2023 diesel summary flags line heater power above the expected value within 2.2 s of continuous monitoring. On the 2014 6.6L LML, GM read the line heater conductance and set the code at 0.92 S or more, Type B. P221C is the low-current partner, P20BF a low control circuit.
- What you may notice
- Malfunction indicator lamp on after one trip (GM)
- Line heater switched off, DEF may stay frozen in cold weather
- Likely causes
- LikelyPartly shorted heating element in the DEF pressure line
- PossibleHeater lead chafed to ground
- RareWater in the line heater connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.