U3535: High Voltage System Interlock Circuit L

What it means

Generic fault on HVIL loop L. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

HVIL loop L is a low-voltage safety circuit that verifies the secure connection of high-voltage connectors and covers. This code identifies a general fault on loop L, without specifying whether its signal is low, high, or out of pattern; a connector that is not fully mated is one possible cause. Gateway or CAN problems may also affect reported status, so compare this code with network faults.

Common causes

Most likely first.

1. HV connector not fully mated
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Save freeze-frame data and scan all modules for U3535, related HVIL codes, and communication faults before clearing anything.
2. Check scan-tool live data for loop L status and note whether the reported state changes when the fault is present.
3. With the vehicle safely powered down using the manufacturer's high-voltage procedure, inspect accessible loop L connectors and wiring for incomplete seating, damage, or contamination.
4. Have a qualified technician test loop L continuity and signal behavior using the manufacturer's diagnostic procedure.
5. If loop L wiring and connections pass, check gateway routing and CAN termination for faults affecting the reported loop L data.

Common fixes

• Fully seat a loose loop L interlock connector using the vehicle's specified procedure.
• Clean or repair damaged low-voltage loop L terminals and wiring.
• Replace a confirmed faulty loop L interlock connector or component.
• Correct a verified gateway routing or CAN termination fault.

Can I keep driving?

If a high-voltage warning appears, propulsion is reduced, or the vehicle shuts down, stop driving when safe and arrange prompt diagnosis. Do not unplug or handle high-voltage connectors yourself.