Network, generic (extended)

U3503 Control Module Input Power A Circuit Intermittent/Erratic

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U3503 stands for a supply A that keeps jumping: mostly correct, but with brief dropouts or spikes, so the module sees erratic readings or restarts. What sets it apart from U3501 and U3502 is the pattern rather than the level: short interruptions, fast swings between samples or repeated resets. No manufacturer documents U3503 publicly. GM's brake booster tables show how short supply check windows can be (0.09 s), and that is the time scale on which a loose crimp or a cracked solder joint becomes visible. Look for loose terminals, fuses with weak clamping, chafed wires near moving parts and grounds shared with large loads; wiggle tests while the engine idles, with a scope or min/max recording help, because a plain multimeter averages such events away.

Likely causes

Loose crimp, pin or fuse contact in feed A
Chafed wire making intermittent contact
Ground shared with heavy loads causing dips
Cracked solder joint inside the module

Symptoms

  • Sporadic resets or brief function dropouts
  • Code returns over bumps or when loads switch

Repair estimate

DifficultyMediumDIY possible
Parts and labour€10–500
Time0.5–3 h

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

Parts involved

module power apower wiring

Related codes

U3500U3501U3502U3507U350B

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