Fault Family System: Powertrain (P-Codes) 9 SAE Codes

Stop Start System Circuit

Diagnostic & Technical Explanation

Code P05BC (Stop-Start Mode Switch Circuit/Open) sets when the ECM's automatic engine stop-start system reports an open/shorted mode-switch circuit, an invalid status signal, or a restart that takes longer or shorter than expected. Causes are a failed stop-start disable switch, a weak auxiliary/AGM battery unable to support rapid restarts, a worn starter not rated for the higher cycle count, or software/sensor conditions blocking the stop event (e.g., low battery SOC, cold engine, or A/C demand).

These 9 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 9 times.

Codes in this family (9)

Code	Definition	Repair coverage
P05BC	Stop-Start Mode Switch Circuit/Open	4 ranked fixes
P05BD	Stop-Start Mode Switch Circuit Range/Performance	4 ranked fixes
P05BE	Stop-Start Mode Switch Circuit Low	4 ranked fixes
P05BF	Stop-Start Mode Switch Circuit High	4 ranked fixes
P05F9	Stop-Start Status Signal Circuit	4 ranked fixes
P05FA	Stop-Start Status Signal Circuit Low	4 ranked fixes
P05FB	Stop-Start Status Signal Circuit High	4 ranked fixes
P06EF	Engine Restart Performance	4 ranked fixes
P06F4	Stop-Start Mode Lamp Control Circuit	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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