Fault Family System: Powertrain (P-Codes) 34 SAE Codes

Engine Coolant Bypass Valve Control

Diagnostic & Technical Explanation

Code P2681 (Engine Coolant Bypass Valve A Control Circuit/Open) sets when the ECM detects an open circuit, out-of-range voltage, a range/performance deviation, or a stuck-open/stuck-closed report while driving one of the engine's thermal-management coolant bypass valves (A through D) that hold coolant in the block for faster warm-up and route flow between the radiator, heater core, and oil cooler circuits, and several codes in this family are plain Control Circuit Low or Control Circuit High faults that point directly at an open or shorted valve driver wire. Coolant scale stiffening the rotary valve element until its motor stalls is the leading cause, followed by a failed valve actuator motor and connector corrosion at the valve.

These 34 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 34 times.

Codes in this family (34)

Code	Definition	Repair coverage
P2681	Engine Coolant Bypass Valve A Control Circuit/Open	4 ranked fixes
P2682	Engine Coolant Bypass Valve A Control Circuit Low	4 ranked fixes
P2683	Engine Coolant Bypass Valve A Control Circuit High	4 ranked fixes
P26A3	Engine Coolant Bypass Valve A Range/Performance	4 ranked fixes
P26AB	Engine Coolant Bypass Valve A Stuck/Open	4 ranked fixes
P26AC	Engine Coolant Bypass Valve B Control Circuit/Open	4 ranked fixes
P26AD	Engine Coolant Bypass Valve B Control Circuit Low	4 ranked fixes
P26AE	Engine Coolant Bypass Valve B Control Circuit High	4 ranked fixes
P26AF	Engine Coolant Bypass Valve B Stuck/Open	4 ranked fixes
P26B0	Engine Coolant Bypass Valve B Range/Performance	4 ranked fixes
P26B1	Engine Coolant Bypass Valve A Stuck Closed	4 ranked fixes
P26B2	Engine Coolant Bypass Valve B Stuck Closed	4 ranked fixes
P26B7	Engine Coolant Bypass Valve C Control Circuit/Open	4 ranked fixes
P26B8	Engine Coolant Bypass Valve C Control Circuit Low	4 ranked fixes
P26B9	Engine Coolant Bypass Valve C Control Circuit High	4 ranked fixes
P26BA	Engine Coolant Bypass Valve C Stuck/Open	4 ranked fixes
P26BB	Engine Coolant Bypass Valve C Range/Performance	4 ranked fixes
P26BC	Engine Coolant Bypass Valve C Stuck Closed	4 ranked fixes
P26BD	Engine Coolant Bypass Valve D Control Circuit/Open	4 ranked fixes
P26BE	Engine Coolant Bypass Valve D Control Circuit Low	4 ranked fixes
P26BF	Engine Coolant Bypass Valve D Control Circuit High	4 ranked fixes
P26C0	Engine Coolant Bypass Valve D Stuck/Open	4 ranked fixes
P26C1	Engine Coolant Bypass Valve D Range/Performance	4 ranked fixes
P26C2	Engine Coolant Bypass Valve D Stuck Closed	4 ranked fixes
P2CF8	Engine Coolant Bypass Valve D Control Circuit Driver Current/Temperature Too High	4 ranked fixes
P2DE7	Cold Start Engine Coolant Bypass Valve C Range/Performance	4 ranked fixes
P2DE8	Cold Start Engine Coolant Bypass Valve D Stuck Open	4 ranked fixes
P2E62	Engine Coolant Bypass Valve E Control Circuit/Open	4 ranked fixes
P2E63	Engine Coolant Bypass Valve E Control Circuit Low	4 ranked fixes
P2E64	Engine Coolant Bypass Valve E Control Circuit High	4 ranked fixes
P2E65	Engine Coolant Bypass Valve E Stuck/Open	4 ranked fixes
P2E66	Engine Coolant Bypass Valve E Range/Performance	4 ranked fixes
P2E67	Engine Coolant Bypass Valve E Stuck Closed	4 ranked fixes
P2E81	Cold Start Engine Coolant Bypass Valve D Stuck Closed	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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