U3537 code meaning
High Voltage System Interlock Circuit L Low
Network system Generic code U35xx codes Check engine light
What U3537 means
U3537 is logged for an insufficient reading on loop L. The cause may lie outside the loop itself. In a Volvo patent with paired loops for trucks with separate high-voltage buses, neither loop is closed before the current sources start; one loop only closes once the source of the other energises the coil of an isolated relay. If that partner source stays off, or the relay coil or its contacts fail, the dependent loop reads as open though its own plugs are fine. With such a design, a low result on loop L calls for checking the codes and source of the coupled loop and the relay before any wiring is opened. No maker documents U3537; the contactors behind loop L stay open.
U3537 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 U3537
- Vehicle or one high-voltage bus does not become ready
- Interlock codes for more than one loop stored at once
Common causes of U3537
- Most likelyPlug within loop L disconnected or wire shorted to ground
- PossibleSource of a coupled loop not running, so the coupling relay stays open
- Less likelyCoupling relay between loops with failed coil or contact
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvil loop lHvil wiring
What each part of U3537 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 37 | The exact fault in that area. |
What to do next
- Note U3537 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 U3537
What does U3537 mean?
U3537 means "High Voltage System Interlock Circuit L Low". U3537 is logged for an insufficient reading on loop L. It is a generic code, so it means the same on every make.
Is it safe to drive with U3537?
Drive gently and only to a workshop. With U3537 the car can go into limp mode (reduced power) to protect itself.
Will U3537 fail an emissions test?
U3537 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 U3537 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U3537 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.