U3518 code meaning
High Voltage System Interlock Circuit C High
Network system Generic code U35xx codes Check engine light
What U3518 means
U3518 is stored when loop C reads above its upper limit, usually a loop wire shorted to 12 V, to the wire of another loop in a shared connector, or a source stage that no longer switches off. Volvo's two-loop patent couples loops only through a galvanically isolated relay, so foreign voltage from one loop is not meant to reach another; where wires of different loops share a connector, damage can still bridge them. Ford's patent stores a code and switches on its Service Soon lamp once an interlock circuit is shorted high, and Texas Instruments shows that the loop current then stops following the commanded pattern. No maker documents U3518. The HV system stays off; inspect connectors that carry interlock pins of several loops first.
U3518 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 U3518
- No ready mode despite all HV connectors being in place
- Service or HV warning lamp lit
- High codes for more than one interlock loop
Common causes of U3518
- Most likelyInterlock wire of loop C shorted to 12 V
- PossibleLoop C bridged to another loop's wire in a shared connector
- Less likelyInterlock source for loop C stuck on in the module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvil loop cHvil wiring
What each part of U3518 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 18 | The exact fault in that area. |
What to do next
- Note U3518 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 U3518
What does U3518 mean?
U3518 means "High Voltage System Interlock Circuit C High". U3518 is stored when loop C reads above its upper limit, usually a loop wire shorted to 12 V, to the wire of another loop in a shared connector, or a source stage that no longer switches off. It is a generic code, so it means the same on every make.
Is it safe to drive with U3518?
Drive gently and only to a workshop. With U3518 the car can go into limp mode (reduced power) to protect itself.
Will U3518 fail an emissions test?
U3518 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 U3518 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U3518 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.