P056D code meaning
Reductant Control Module System Voltage
Powertrain system Generic code P05xx codes Check engine light
What P056D means
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.
P056D at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P056D
- Check engine light and DEF warning
- Possible countdown to start inhibit or power limit
- Further SCR codes
Common causes of P056D
- Most likelyFuse, relay or supply line of the DEF module
- PossibleCorrosion at module connector or ground (underbody, road salt)
- PossibleSystem under- or overvoltage
- Less likelyModule faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant control moduleModule power supplyModule ground
What each part of P056D means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 6D | The exact fault in that area. |
What to do next
- Note P056D and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P056D
What does P056D mean?
P056D means "Reductant Control Module System Voltage". Diesels with SCR may have a separate module for AdBlue/DEF dosing (pump, heaters, dosing valve) talking to the engine module over CAN. It is a generic code, so it means the same on every make.
Is it safe to drive with P056D?
Drive gently and only to a workshop. With P056D the car can go into limp mode (reduced power) to protect itself.
Will P056D fail an emissions test?
Yes, it can. P056D is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P056D to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P056D clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.