Fault Family System: Powertrain (P-Codes) 4 SAE Codes

Reductant System Leak Flow

Diagnostic & Technical Explanation

Code P2D1D (Reductant System Leak Detected – Small Leak) sets when the ECM's reductant system diagnostic detects a small or large leak in the DEF supply lines, or finds dosing flow restricted or fully blocked on its way to the injector. A leak is most often a degraded quick-connect fitting or a cracked line from freeze-thaw cycling, while restricted or blocked flow points to crystallized DEF plugging a line or filter after an incomplete purge.

These 4 diagnostic trouble codes share one detection mechanism and one repair path, which is why MechanicDB groups them into a single authored fault family rather than repeating the same explanation 4 times.

Codes in this family (4)

Code	Definition	Repair coverage
P2D1D	Reductant System Leak Detected – Small Leak	4 ranked fixes
P2D1E	Reductant System Leak Detected – Large Leak	4 ranked fixes
P2D1F	Reductant System Flow – Restricted	4 ranked fixes
P2D20	Reductant System Flow – Blocked	4 ranked fixes

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)

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