System: Powertrain (P-Code)
SAE Standard (Generic)
Family: Control Module System Voltage Circuit
Code P056D: Reductant Control Module System Voltage
Diagnostic & Technical Explanation
Code P056D (Reductant Control Module System Voltage) sets when a smart control module (glow plug control module, oxygen sensor control module, or reductant/SCR control module) reports its own supply voltage is out of the expected range on its power feed. Causes are a blown fuse, a corroded power or ground connection at the module, a failing charging system, or an internal module power-supply fault.
First-listed procedure
Rank #1
Check module power feed fuse and ground
Easy DIY
This is the first procedure in the authored
consideration order, not a measured cause likelihood. Execute it only when its prerequisites
and diagnostic findings support it. Its cost and labor estimates (where known), the step-by-step procedure and the
remaining 3 procedure(s) are in the licensed dataset. Ordering context.
Full family: Control Module System Voltage Circuit
What this page does not show
This page publishes the fault mechanism and the code index. The licensed dataset adds, for
every one of the 15,886 codes, the full authored repair set (56,729 procedures in total)
with the fields deliberately withheld here:
- Procedures 2..n after the first-listed procedure
- Aftermarket parts cost ranges in USD (
est_parts_cost_min/max_usd)
- Professional labor-hour estimates (
est_labor_hours)
- Step-by-step diagnostic and repair instructions
- Replacement-part mappings and catalog lookups
- 6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)