Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P056D Reductant Control Module System Voltage

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Diesels with SCR may have a separate module for AdBlue/DEF dosing (pump, heaters, dosing valve) talking to the engine module over CAN. It measures its supply; outside its window no safe dosing is possible, so dosing and SCR diagnoses are suspended and NOx rises, and if it persists the SCR warnings and power limits apply. No manufacturer document available to us uses P056D – Ford's diesel reports the dosing module supply as P21CB below 8.5 V and P21CC above 19 V. CARB requires SCR modules to be monitored.

Likely causes

Fuse, relay or supply line of the DEF module
Corrosion at module connector or ground (underbody, road salt)
System under- or overvoltage
Module faulty

Symptoms

  • Check engine light and DEF warning
  • Possible countdown to start inhibit or power limit
  • Further SCR codes

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€30–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant control modulemodule power supplymodule ground

Related codes

P21CBP21CCP20FFP0562P0563P055E

References: fordservicecontent.com, law.cornell.edu.