U353CHigh Voltage System Interlock Circuit M High
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U353C indicates that loop M exceeds its upper threshold. A loop built from known resistances can be checked point by point. In Tesla's Model S tech note the battery management sends a constant 20 mA through four resistance stages of 60 ohms, 240 ohms in total, so about 4.8 V appears at the start and the value falls to 3.6, 2.4 and 1.2 V at the following connectors. Back-probing each point and comparing it with these steps shows in which section extra resistance or foreign voltage sits; resistance to ground with the loop off runs in matching 60-ohm steps. A wiring diagram with such reference values makes loop M quick to trace. No maker documents U353C itself.
- What you may notice
- Vehicle does not become ready
- High-voltage warning returns after clearing
- Likely causes
- LikelyCorroded or loose contact adding resistance in one section of loop M
- PossibleLoop M wire in contact with a 12 V supply
- RareHigh-voltage component with internal loop resistance out of specification
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.