U353C code meaning
High Voltage System Interlock Circuit M High
Network system Generic code U35xx codes Check engine light
What U353C means
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.
U353C at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U353C
- Vehicle does not become ready
- High-voltage warning returns after clearing
Common causes of U353C
- Most likelyCorroded or loose contact adding resistance in one section of loop M
- PossibleLoop M wire in contact with a 12 V supply
- Less likelyHigh-voltage component with internal loop resistance out of specification
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvil loop mHvil wiring
What each part of U353C means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 3C | The exact fault in that area. |
What to do next
- Note U353C and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U353C
What does U353C mean?
U353C means "High Voltage System Interlock Circuit M High". U353C indicates that loop M exceeds its upper threshold. It is a generic code, so it means the same on every make.
Is it safe to drive with U353C?
Drive gently and only to a workshop. With U353C the car can go into limp mode (reduced power) to protect itself.
Will U353C fail an emissions test?
U353C is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U353C to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U353C clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.