U3543 code meaning
High Voltage System Interlock Circuit O Low
Network system Generic code U35xx codes Check engine light
What U3543 means
With U3543, loop O has dropped under its minimum. Some plug designs let the fitter see the reason. An LG Electronics patent describes a high-voltage connector closed by turning a cover housing: the rotation moves an inner cap up or down so that the power terminals mate first and the shorter interlock tab last, while a scale on the plug housing shows how far the cover has turned. A cover left short of its end stop keeps the power pins engaged with the interlock still apart, exactly the picture of a low reading. No maker documents U3543. Turn each rotary plug on loop O fully home and check the scale.
U3543 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 U3543
- High voltage stays off after work on HV plugs
- No ready mode
- Charging not possible
Common causes of U3543
- Most likelyRotary HV plug on loop O not turned to its end position
- PossibleInterlock tab or socket in a loop O plug bent or pushed back
- PossibleLoop O wire shorted to ground
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvil loop oHvil wiring
What each part of U3543 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 43 | The exact fault in that area. |
What to do next
- Note U3543 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 U3543
What does U3543 mean?
U3543 means "High Voltage System Interlock Circuit O Low". With U3543, loop O has dropped under its minimum. It is a generic code, so it means the same on every make.
Is it safe to drive with U3543?
Drive gently and only to a workshop. With U3543 the car can go into limp mode (reduced power) to protect itself.
Will U3543 fail an emissions test?
U3543 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 U3543 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U3543 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.