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U3516 High Voltage System Interlock Circuit C Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3516 flags loop C as electrically present but untrustworthy: resistance, timing or pattern of the returned signal fall outside what the module accepts, often only for moments. As the U35xx series has no intermittent code for loops B and C, unlike P0A0E for loop A, short dropouts will probably be stored here. The interlock patent from CATL names contact impedance, supply ripple and static discharge as sources of false trips, and Mercedes' bulletin for model line 243 links its interlock codes to oxidised low-voltage pins, bent pins at HV components and twisted harness runs; it adds that the HV component itself is rarely to blame. No maker documents U3516. Drivers notice HV shutdowns that come and go, often after rough roads or rain.

Likely causes

Loose or spread contact in a connector of loop C
Oxidised low-voltage interlock pins
Twisted or strained harness section moving with the body
Static discharge or interference on the interlock line

Symptoms

  • Sporadic loss of ready mode
  • HV warning that appears and clears by itself
  • Fault hard to reproduce in the workshop

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,500
Time1–6 h

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

Parts involved

hvil loop c

Related codes

U3515U3517U3518U3512P0A0E

References: patents.google.com, static.nhtsa.gov, law.cornell.edu.