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U3500 Control Module Input Power A Circuit Range/Performance

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U3500 says that supply input A of a module is present but its voltage is implausible, for example outside the window expected for the current power mode or contradicting other measurements, without clearly passing a lower or upper limit. It thus sits between U3006, which reports a missing or open feed, and the hard limit codes U3501 and U3502. Which pin is A is up to the manufacturer; in GM's electric brake booster tables (2016–2019 hybrid) A is the module's own logic and CAN supply, watched for under 7.5 V and over 16 V, but GM uses only the Low and High codes there. No manufacturer documents U3500 publicly. Typical causes are a high-resistance contact that sags under load, a poor ground or a drifting internal measurement.

Likely causes

High-resistance terminal or fuse contact on feed A
Poor module ground shifting the measured supply
Drifting voltage measurement inside the module

Symptoms

  • Functions of the module dropping out or behaving inconsistently
  • Code returns mainly under electrical load

Repair estimate

DifficultyMediumDIY possible
Parts and labour€10–500
Time0.3–2.5 h

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

Parts involved

module power apower wiring

Related codes

U3501U3502U3503U3006U3504

References: law.cornell.edu, gsi.ext.gm.com.