U3537High Voltage System Interlock Circuit L Low
- Generic OBD-II code · Network
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Vehicle or one high-voltage bus does not become ready
- Interlock codes for more than one loop stored at once
- Likely causes
- LikelyPlug within loop L disconnected or wire shorted to ground
- PossibleSource of a coupled loop not running, so the coupling relay stays open
- RareCoupling relay between loops with failed coil or contact
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.