Network, generic (extended)

U353B High Voltage System Interlock Circuit M Low

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U353B is set when loop M reads too low. A lever-type plug can leave it in exactly that state on purpose. A connector patent by Hyundai and Kia adds an intermediate lock to the lever: on the way out it stops at a point where the interlock contacts are already apart while the power terminals still touch, so the system has time to switch off before the second lever movement separates the plug. If such a plug is left at the intermediate stage after service, or not pushed fully home, loop M stays open although the plug seems attached. Check every lever on the loop for its final locked position. No maker documents U353B; the contactors remain open.

Likely causes

Lever-type connector in loop M left at its intermediate position
Loop M wire shorted to ground
Loop M source in the controller failed

Symptoms

  • No ready mode after service on high-voltage plugs
  • Fault persists after clearing

Repair estimate

DifficultyHardWorkshop job
Parts and labour€60–1,200
Time0.5–4 h

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

Parts involved

hvil loop mhvil wiring

Related codes

U3539U353AU353CU3537P0A0C

References: patents.google.com, law.cornell.edu.