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U063F Lost Communication With Engine Coolant Flow Control Valve Position Sensor

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

The coolant flow control valve meters how much coolant passes through the engine, and its position sensor often transmits over SENT, a one-way digital protocol with a frame every few milliseconds. U063F flags the loss of that stream. GM's 2025 diesel tables (25OBDG04B) treat it as a Type B fault, with the MIL on the second trip, when 80 of 100 samples taken every 6.25 ms are bad: the last valid SENT frame is older than 6.25 ms while the line sits steady low or high, SENT frame errors are counted, or the pulse counter stops updating. The powertrain relay must supply more than 11 V and the engine must not be cranking. GM's harness chafing bulletin 21-NA-149 for 2019 to 2022 trucks and SUVs lists U063F among many codes. Analog-type sensor faults are P2B5D to P2B60 and P2B6D.

Likely causes

Engine harness chafed through to the SENT, supply or ground wire (GM 21-NA-149)

Corroded or loose connector at the flow control valve

Position sensor electronics in the valve failed (usually replaced with the valve)

SENT input of the engine control module faulty

Symptoms

Check engine light after two trips
Coolant temperature control less precise, slower warm-up or higher temperatures

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€50–900

Time0.5–3 h

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

Parts involved

coolant flow valve position sensorvehicle bus wiring

References: gsi.ext.gm.com, static.nhtsa.gov, en.wikipedia.org.