U353AHigh Voltage System Interlock Circuit M Performance
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- U353A flags loop M as questionable rather than plainly open or shorted. Redundant monitoring can produce exactly that state. NIO patented an interlock fed by two signal generators whose pulse trains overlap on one line; with duty ratios A and B the detector expects a combined average of A plus B minus their product. If only one part arrives, the system can keep the contactors closed and name the generator whose share is missing as a fault candidate, though the real cause may sit outside it. The aim is to avoid needless shutdowns caused by a failing monitoring part. Under such logic a performance code may be logged while the vehicle still drives. No maker documents U353A.
- What you may notice
- Warning lamp while the vehicle keeps driving
- Occasional loss of high voltage if the second channel also degrades
- Likely causes
- PossibleOne of the loop M signal sources weak or failed
- PossibleLoose contact in a loop M connector distorting the signal
- RareDetection circuit for loop M faulty
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €100 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.