OBD-II code · Powertrain (generic)
P056D Reductant Control Module System Voltage
The reductant (AdBlue) control module reports its supply voltage outside the calibrated window. Reductant dosing is suspended until voltage returns to range, which can drive NOx emissions out of compliance.
Is it safe to drive with P056D?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySupply voltage low
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
- Often, with basic tools
- Typical labour
- 0.6–2 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Control Module, Reductant Supply Relay
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.