P21CCReductant Control Module Supply Voltage 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
- P21CC is the overvoltage counterpart of P21CB: the DEF control module sees a supply above what its electronics are designed for. Ford's 2023 diesel summary checks the reductant pump controller in a continuous loop and sets P21CC once its supply exceeds 19 V, deciding within 5 s. On a 12 V vehicle such values usually come from a charging system whose regulator has failed, from a jump start with a 24 V source, or from load dumps on a loose battery terminal; less often the module measures its own input wrongly. To protect pump and heaters the module usually stops working, so dosing pauses. GM's published diesel tables list only the low case. P21CA is the general supply code, and P0563 shows whether the engine module sees the same excess.
- What you may notice
- Check engine light on
- DEF dosing paused, SCR warning
- Battery or charging warning, bulbs unusually bright
- Likely causes
- LikelyAlternator voltage regulator overcharging
- PossibleJump start or charging with excessive voltage
- PossibleLoose battery terminal causing voltage spikes
- RareModule's own voltage measurement faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €0 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.