U353B code meaning
High Voltage System Interlock Circuit M Low
Network system Generic code U35xx codes Check engine light
What U353B means
U353B is set when loop M reads too low. A lever-type plug can leave it in exactly that state on purpose. A connector patent by Hyundai and Kia adds an intermediate lock to the lever: on the way out it stops at a point where the interlock contacts are already apart while the power terminals still touch, so the system has time to switch off before the second lever movement separates the plug. If such a plug is left at the intermediate stage after service, or not pushed fully home, loop M stays open although the plug seems attached. Check every lever on the loop for its final locked position. No maker documents U353B; the contactors remain open.
U353B 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 U353B
- No ready mode after service on high-voltage plugs
- Fault persists after clearing
Common causes of U353B
- Most likelyLever-type connector in loop M left at its intermediate position
- PossibleLoop M wire shorted to ground
- Less likelyLoop M source in the controller failed
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 U353B means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 3B | The exact fault in that area. |
What to do next
- Note U353B 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 U353B
What does U353B mean?
U353B means "High Voltage System Interlock Circuit M Low". U353B is set when loop M reads too low. It is a generic code, so it means the same on every make.
Is it safe to drive with U353B?
Drive gently and only to a workshop. With U353B the car can go into limp mode (reduced power) to protect itself.
Will U353B fail an emissions test?
U353B 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 U353B to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U353B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.