OBD-II code · Powertrain (generic, extended)
P21C7 Reductant Control Module Power Relay Control Circuit/Open
The control circuit for the relay that supplies power to the SCR/reductant control module is open — module loses main supply on shutdown or never wakes up.
Is it safe to drive with P21C7?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyRelay coil open
- Less likelyPin pushed back out of connector body
- Less likelyCracked solder joint inside the module or sensor
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
- 0.5–2 h
- Emissions test
- Likely to fail
- Parts involved
- Scr Control Module, Power Relay
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.