Fault Family System: Powertrain (P-Codes) 10 SAE Codes

ECM Power Relay Circuit

Diagnostic & Technical Explanation

Code P0685 (ECM/PCM Power Relay Control Circuit/Open) sets when the ECM detects an open circuit, out-of-range voltage, or mistimed de-energization while controlling or sensing its own main power relay, which keeps the module powered briefly after key-off to complete shutdown routines. Causes are a failed power relay, a blown fuse, a corroded relay socket, or damaged control/sense wiring.

These 10 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 10 times.

Codes in this family (10)

Code	Definition	Repair coverage
P0685	ECM/PCM Power Relay Control Circuit/Open	4 ranked fixes
P0686	ECM/PCM Power Relay Control Circuit Low	4 ranked fixes
P0687	ECM/PCM Power Relay Control Circuit High	4 ranked fixes
P0688	ECM/PCM Power Relay Sense Circuit/Open	4 ranked fixes
P0689	ECM/PCM Power Relay Sense Circuit Low	4 ranked fixes
P068A	ECM/PCM Power Relay De-Energized Performance - Too Early	4 ranked fixes
P068B	ECM/PCM Power Relay De-Energized Performance - Too Late	4 ranked fixes
P0690	ECM/PCM Power Relay Sense Circuit High	4 ranked fixes
P2510	ECM/PCM Power Relay Sense Circuit Range/Performance	4 ranked fixes
P2511	ECM/PCM Power Relay Sense Circuit Intermittent	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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