U3516High Voltage System Interlock Circuit C Performance
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Sporadic loss of ready mode
- HV warning that appears and clears by itself
- Fault hard to reproduce in the workshop
- Likely causes
- LikelyLoose or spread contact in a connector of loop C
- PossibleOxidised low-voltage interlock pins
- PossibleTwisted or strained harness section moving with the body
- RareStatic discharge or interference on the interlock line
- 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.