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U0615 Lost Communication With Engine Coolant Bypass Valve A

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Engines with split cooling circuits often route coolant through an electrically driven valve that reports its position and status digitally. U0615 is stored when the engine controller gets no answer from bypass valve A. In GM's 2019 hybrid tables (19OBDG01) the valve sits on a LIN bus: once Run mode and at least 11 V have held for 400 ms, three missed responses fail the test as Type B, and the valve's own position check (P15C5) is suspended meanwhile. Ram's bulletin 08-171-26 for 2025-26 Ram 2500 to 5500 trucks links U0615 on the coolant three-way valve to a contaminated connector under the coolant bottle; the fix is dielectric grease, or a new valve plus pigtail. Drivers notice the lamp and weak cabin heat. Circuit faults of the valve are P2681 to P2683.

Likely causes

Moisture or corrosion in the valve connector (Ram bulletin 08-171-26)

LIN, supply or ground wire to the valve open, shorted or chafed

Valve actuator electronics failed (valve no longer answers)

LIN master in the engine controller faulty

Symptoms

Check engine light
Little or no cabin heat
Engine warms up slower or coolant temperature behaves unusually

Repair estimate

DifficultyMediumDIY possible

Parts and labour€30–700

Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

coolant bypass valve avehicle bus wiring

References: static.nhtsa.gov, gsi.ext.gm.com, law.cornell.edu.