U3517 code meaning
High Voltage System Interlock Circuit C Low
Network system Generic code U35xx codes Check engine light
What U3517 means
U3517 says the level read back on interlock loop C stays too low. Depending on the design, an opened plug in loop C, a wire chafed to ground or a failed source in the monitoring module all lead to it. In current-fed designs such as the Texas Instruments reference circuit, a short to ground draws extra supply current while an opened loop does not, which helps to separate the two. For loop A, GM uses a 5 V test voltage and a 30 % lower limit, which indicates the margins involved. Mercedes has technicians measure interlock loop resistance segment by segment on model line 243, a method that suits loop C just as well. No manufacturer publishes U3517 itself. Until the fault is cleared, the contactors remain open.
U3517 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 U3517
- Vehicle cannot be started
- HV system warning in the instrument cluster
- Charging unavailable
Common causes of U3517
- Most likelyInterlock wire of loop C chafed to ground at a module or the body
- PossibleConnector in loop C unplugged, sensed as a low signal
- PossibleBroken interlock connector housing or terminal
- Less likelySource stage for loop C failed in the monitoring 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 U3517 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 17 | The exact fault in that area. |
What to do next
- Note U3517 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 U3517
What does U3517 mean?
U3517 means "High Voltage System Interlock Circuit C Low". U3517 says the level read back on interlock loop C stays too low. It is a generic code, so it means the same on every make.
Is it safe to drive with U3517?
Drive gently and only to a workshop. With U3517 the car can go into limp mode (reduced power) to protect itself.
Will U3517 fail an emissions test?
U3517 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 U3517 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U3517 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.