OBD-II code · Powertrain (generic, extended)
P21CC Reductant Control Module Supply Voltage High
SCR control module supply voltage above the upper threshold — overvoltage.
Is it safe to drive with P21CC?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyCharging system overvoltage
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–3 h
- Emissions test
- Likely to fail
- Parts involved
- Scr Control Module
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.