Network, generic

U0644 Lost Communication With Wastegate Position Sensor A

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Engine harness chafed at brackets or covers
Connector at the wastegate actuator loose or corroded
Position sensor in the actuator failed
Low supply voltage or poor ground

Symptoms

  • MIL on from the first trip
  • Reduced engine power, boost limited
  • Several other engine codes when the harness is damaged

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–900
Time0.5–3 h

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

Parts involved

wastegate position sensor avehicle bus wiring

Related codes

U0674P2AB7P2AB8P2AB9P2B81P2B93U0643

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