U063F code meaning
Lost Communication With Engine Coolant Flow Control Valve Position Sensor
Network system Generic code U06xx codes Check engine light
What U063F means
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.
U063F at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U063F
- Check engine light after two trips
- Coolant temperature control less precise, slower warm-up or higher temperatures
Common causes of U063F
- Most likelyEngine harness chafed through to the SENT, supply or ground wire (GM 21-NA-149)
- PossibleCorroded or loose connector at the flow control valve
- PossiblePosition sensor electronics in the valve failed (usually replaced with the valve)
- Less likelySENT input of the engine control module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Coolant flow valve position sensorVehicle bus wiring
What each part of U063F means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 3F | The exact fault in that area. |
What to do next
- Note U063F and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U063F
What does U063F mean?
U063F means "Lost Communication With Engine Coolant Flow Control Valve Position Sensor". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with U063F?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U063F fail an emissions test?
Yes, it can. U063F is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U063F to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U063F clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.