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U063E Lost Communication With Exhaust Heat Exchanger Bypass Valve Actuator A

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Exhaust heat recovery passes hot exhaust through a coolant heat exchanger after a cold start, so the engine and cabin warm up sooner; a flap later diverts the gas around it. When that flap's actuator is a LIN slave, losing it gives U063E. GM documents the check in its hybrid tables 16OBDG02 through 19OBDG02, run by the second hybrid powertrain control processor: with the controller on, Run/Crank active, LIN enabled for at least 2 s and battery voltage at least 10.2 V, 80 missed replies at 40 ms intervals (3.2 s) fail it as Type B, MIL after two trips. A stuck flap can slow warm-up or keep heating the coolant when it should not. Circuit and position faults of the flap are P237C to P237F and P2C22 to P2C25; actuator B is U066C.

Likely causes

Actuator electronics damaged by heat near the exhaust

LIN or supply wiring under the vehicle damaged or corroded

Water ingress or corrosion in the actuator connector

Weak 12 V supply interrupting LIN communication

Symptoms

MIL after two drive cycles
Slower engine and cabin warm-up in cold weather
Engine runs longer on hybrids to reach operating temperature

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

exhaust heat exchanger bypass actuator avehicle bus wiring

References: gsi.ext.gm.com, gsi.ext.gm.com, en.wikipedia.org.