U3516 code meaning
High Voltage System Interlock Circuit C Performance
Network system Generic code U35xx codes Check engine light
What U3516 means
U3516 flags loop C as electrically present but untrustworthy: resistance, timing or pattern of the returned signal fall outside what the module accepts, often only for moments. As the U35xx series has no intermittent code for loops B and C, unlike P0A0E for loop A, short dropouts will probably be stored here. The interlock patent from CATL names contact impedance, supply ripple and static discharge as sources of false trips, and Mercedes' bulletin for model line 243 links its interlock codes to oxidised low-voltage pins, bent pins at HV components and twisted harness runs; it adds that the HV component itself is rarely to blame. No maker documents U3516. Drivers notice HV shutdowns that come and go, often after rough roads or rain.
U3516 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U3516
- Sporadic loss of ready mode
- HV warning that appears and clears by itself
- Fault hard to reproduce in the workshop
Common causes of U3516
- Most likelyLoose or spread contact in a connector of loop C
- PossibleOxidised low-voltage interlock pins
- PossibleTwisted or strained harness section moving with the body
- Less likelyStatic discharge or interference on the interlock line
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvil loop c
What each part of U3516 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 16 | The exact fault in that area. |
What to do next
- Note U3516 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 U3516
What does U3516 mean?
U3516 means "High Voltage System Interlock Circuit C Performance". U3516 flags loop C as electrically present but untrustworthy: resistance, timing or pattern of the returned signal fall outside what the module accepts, often only for moments. It is a generic code, so it means the same on every make.
Is it safe to drive with U3516?
Drive gently and only to a workshop. With U3516 the car can go into limp mode (reduced power) to protect itself.
Will U3516 fail an emissions test?
U3516 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 U3516 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will U3516 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.