U3517High Voltage System Interlock Circuit C Low
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U3517 says the level read back on interlock loop C stays too low. Depending on the design, an opened plug in loop C, a wire chafed to ground or a failed source in the monitoring module all lead to it. In current-fed designs such as the Texas Instruments reference circuit, a short to ground draws extra supply current while an opened loop does not, which helps to separate the two. For loop A, GM uses a 5 V test voltage and a 30 % lower limit, which indicates the margins involved. Mercedes has technicians measure interlock loop resistance segment by segment on model line 243, a method that suits loop C just as well. No manufacturer publishes U3517 itself. Until the fault is cleared, the contactors remain open.
- What you may notice
- Vehicle cannot be started
- HV system warning in the instrument cluster
- Charging unavailable
- Likely causes
- LikelyInterlock wire of loop C chafed to ground at a module or the body
- PossibleConnector in loop C unplugged, sensed as a low signal
- PossibleBroken interlock connector housing or terminal
- RareSource stage for loop C failed in the monitoring 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.