Fault Family System: Powertrain (P-Codes) 11 SAE Codes

EGR Flow Performance

Diagnostic & Technical Explanation

Code P0400 (EGR A Flow) sets when the ECM commands a specific EGR flow rate (valve A or valve B on dual-EGR platforms) and the measured intake or exhaust response indicates the actual flow is significantly less or more than commanded. Insufficient flow is most often a carbon-clogged EGR passage, valve, or cooler; excessive flow points to a valve stuck partially open or a failed position sensor causing the ECM to over-command it.

These 11 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 11 times.

Codes in this family (11)

Code	Definition	Repair coverage
P0400	EGR A Flow	4 ranked fixes
P0401	EGR A Flow Insufficient Detected	4 ranked fixes
P0402	EGR A Flow Excessive Detected	4 ranked fixes
P049A	EGR B Flow	4 ranked fixes
P049B	EGR B Flow Insufficient Detected	4 ranked fixes
P049C	EGR B Flow Excessive Detected	4 ranked fixes
P04DD	Cold Start EGR A Flow Insufficient Detected	4 ranked fixes
P04DE	Cold Start EGR A Flow Excessive Detected	4 ranked fixes
P2AA3	Cold Start EGR B Flow Insufficient Detected	4 ranked fixes
P2AA4	Cold Start EGR B Flow Excessive Detected	4 ranked fixes
P2D1C	Cold Start EGR A/B Ratio Performance	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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