U3512High Voltage System Interlock Circuit B Performance
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U3512 is stored when interlock loop B still conducts but behaves implausibly: its resistance drifts outside the permitted window, the returned signal does not follow the test pattern in time, or two readings of the same loop disagree. CATL's interlock patent explains why loops misreport: contact impedance between HV parts, supply fluctuations and static discharge can cause false alarms. Samsung SDI points out that different loops may have different detection and reaction times, so loop B can be judged by other rules than loop A. Oxidised pins, a connector not fully latched or a harness rubbing on the body are likely causes, as Mercedes lists for its interlock codes P0A0A00 to P0A0D00. No maker documents U3512 itself. The HV system may drop out repeatedly rather than stay off.
- What you may notice
- HV system switches off and on again unexpectedly
- Ready mode lost while driving or at start
- Interlock codes in several modules at once
- Likely causes
- LikelyOxidised interlock pins raising the loop resistance
- PossibleConnector in loop B seated but not fully latched
- PossibleHarness rubbing on the body with intermittent contact
- RareInterference or supply ripple distorting the loop signal
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.