U3518High Voltage System Interlock Circuit C High
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U3518 is stored when loop C reads above its upper limit, usually a loop wire shorted to 12 V, to the wire of another loop in a shared connector, or a source stage that no longer switches off. Volvo's two-loop patent couples loops only through a galvanically isolated relay, so foreign voltage from one loop is not meant to reach another; where wires of different loops share a connector, damage can still bridge them. Ford's patent stores a code and switches on its Service Soon lamp once an interlock circuit is shorted high, and Texas Instruments shows that the loop current then stops following the commanded pattern. No maker documents U3518. The HV system stays off; inspect connectors that carry interlock pins of several loops first.
- What you may notice
- No ready mode despite all HV connectors being in place
- Service or HV warning lamp lit
- High codes for more than one interlock loop
- Likely causes
- LikelyInterlock wire of loop C shorted to 12 V
- PossibleLoop C bridged to another loop's wire in a shared connector
- RareInterlock source for loop C stuck on in the module
- Repair
- Hard · 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.