U0644 code meaning
Lost Communication With Wastegate Position Sensor A
Network system Generic code U06xx codes Check engine light
What U0644 means
Pneumatic wastegates have largely given way to electric actuators, and these carry a position sensor so the controller knows how far the bypass flap around the turbine is open. GM reads that sensor on charger A over SENT and, in the 2025 table 25OBDG03B, stores U0644 when message faults appear or a frame is older than 3.13 ms in 10 out of 12 samples taken every 100 ms, with relay voltage of at least 11 V and the engine not cranking; it is Type A, so the MIL comes on in the first trip. GM's harness bulletin PIT5677 for the 2.7L L3B in 2019–2021 Silverado and Sierra 1500 lists U0644 among codes caused by a chafed engine harness. Analog faults would be P2AB7 to P2AB9. Expect reduced power.
U0644 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0644
- MIL on from the first trip
- Reduced engine power, boost limited
- Several other engine codes when the harness is damaged
Common causes of U0644
- Most likelyEngine harness chafed at brackets or covers
- PossibleConnector at the wastegate actuator loose or corroded
- PossiblePosition sensor in the actuator failed
- Less likelyLow supply voltage or poor ground
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Wastegate position sensor aVehicle bus wiring
What each part of U0644 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 44 | The exact fault in that area. |
What to do next
- Note U0644 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 U0644
What does U0644 mean?
U0644 means "Lost Communication With Wastegate Position Sensor A". Pneumatic wastegates have largely given way to electric actuators, and these carry a position sensor so the controller knows how far the bypass flap around the turbine is open. It is a generic code, so it means the same on every make.
Is it safe to drive with U0644?
Drive gently and only to a workshop. With U0644 the car can go into limp mode (reduced power) to protect itself.
Will U0644 fail an emissions test?
Yes, it can. U0644 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 U0644 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0644 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.