Network, generic (extended)

U3511 High Voltage System Interlock Circuit B

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3511 is the general fault of a second high-voltage interlock loop, circuit B. Many vehicles need more than one loop: a Volvo truck patent gives each separate HV bus its own interlock circuit, and a Samsung SDI patent describes extra loops for battery-internal parts such as the service disconnect or the junction box, each with its own source, detector and diagnosis. Which plugs belong to loop B is not published by any maker; GM's OBD tables and Mercedes' model line 243 report all interlock faults with the loop A codes P0A0A–P0A0D. The module sets U3511 when loop B is disturbed but no more precise low, high or performance result applies. The contactors stay open and the vehicle cannot reach ready mode. CARB lists interlock loops as safety-only systems.

Likely causes

HV connector, cover or disconnect in loop B open or not latched after service
Bent, pushed-back or corroded interlock pins
Interlock wiring of loop B chafed or cut
Source or sense stage for loop B in the monitoring module faulty

Symptoms

  • Vehicle does not enter ready mode
  • High-voltage or hybrid system warning in the cluster
  • Charging refused

Repair estimate

DifficultyHardWorkshop job
Parts and labour€80–1,500
Time0.5–4 h

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

Parts involved

hvil loop bhv connectors

Related codes

U3512U3513U3514U3515P0A0A

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