U3520 code meaning
High Voltage System Interlock Circuit E High
Network system Generic code U35xx codes Check engine light
What U3520 means
U3520 means the fifth interlock loop sits above its permitted range, usually because a loop wire has picked up battery voltage or another low-voltage feed. Lear's patent for a pulsed interlock tester shows how to pin this down further: it measures current at generator and detector pins and, by comparing them, works out at which end the unwanted link to the 12 V side lies. Simpler controllers only see the raised level. No manufacturer has published U3520. In the workshop, test each loop E wire against 12 V with the plugs at both ends disconnected; wet or corroded connectors next to fused feeds are typical spots.
U3520 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 U3520
- No ready mode, high-voltage warning shown
- Fault reappears directly after clearing
Common causes of U3520
- Most likelyLoop E wire shorted to a 12 V supply
- PossibleWater or corrosion bridging a loop pin to a supply pin
- Less likelyLoop source in the controller stuck on
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvil loop eHvil wiring
What each part of U3520 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 20 | The exact fault in that area. |
What to do next
- Note U3520 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 U3520
What does U3520 mean?
U3520 means "High Voltage System Interlock Circuit E High". U3520 means the fifth interlock loop sits above its permitted range, usually because a loop wire has picked up battery voltage or another low-voltage feed. It is a generic code, so it means the same on every make.
Is it safe to drive with U3520?
Drive gently and only to a workshop. With U3520 the car can go into limp mode (reduced power) to protect itself.
Will U3520 fail an emissions test?
U3520 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 U3520 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U3520 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.