U3523High Voltage System Interlock Circuit F Low
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U3523 is logged when loop F reads too low, typically from an open plug or a wire shorted to ground. Tracing it means working close to high-voltage parts. The German statutory accident insurance DGUV lets only trained high-voltage staff de-energise the system and insists on the order: isolate, secure against switching back on, then prove absence of voltage with a suitable tester, not a multimeter. Only then open loop F plugs, measure sections or bridge the loop for a test; a bridge must never stay in place, as it defeats the protection. No maker documents U3523. The vehicle stays without high voltage until the cause is fixed.
- What you may notice
- Vehicle not ready to drive, high-voltage warning shown
- Charging not possible
- Likely causes
- LikelyPlug in loop F open or not engaged after service
- PossibleLoop F wire shorted to ground
- PossibleBroken interlock connector housing or locking tab
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.