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U041A Invalid Data Received From Battery Isolation/Voltage Stabilization Control Module

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U041A refers to the battery isolation or voltage stabilization module, which separates an auxiliary battery or sensitive loads from the starter circuit, so a restart after an automatic engine stop leaves the rest of the electrical system at stable voltage. GM's patent US 9,803,608 builds such an isolator from MOSFET switches. A receiver logs it once the module's status frames still arrive but are rejected as invalid. No manufacturer documents U041A publicly. Ford shows the module family on the 2021-2022 F-150 3.5 L PowerBoost, where lost contact (U061E) turns on the wrench lamp and a weak ground GD132 or a failed auxiliary battery isolator is blamed (SSM 50843); checking ground and auxiliary battery first makes sense for U041A as well. Expect stop-start to be disabled; a MIL is unlikely.

Likely causes

Poor ground connection of the isolation module
Weak auxiliary battery making the module report implausible values
Battery isolator or stabilizer internally faulty

Symptoms

  • Automatic stop-start not available
  • Battery or charging system message

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–700
Time0.5–2.5 h

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

Parts involved

battery isolation modulecan bus wiring

Related codes

U061E

References: static.nhtsa.gov, patents.google.com.