U3511High Voltage System Interlock Circuit B
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Vehicle does not enter ready mode
- High-voltage or hybrid system warning in the cluster
- Charging refused
- Likely causes
- LikelyHV connector, cover or disconnect in loop B open or not latched after service
- PossibleBent, pushed-back or corroded interlock pins
- PossibleInterlock wiring of loop B chafed or cut
- RareSource or sense stage for loop B in the monitoring module faulty
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.