U3538: High Voltage System Interlock Circuit L High

What it means

HVIL loop L voltage above expected range. 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 checks whether high-voltage connectors and covers are securely closed. U3538 sets when the loop L voltage is above the expected range, often because the circuit is open. Gateway or CAN communication problems can affect related reports, so compare this code with faults from other modules.

Common causes

Most likely first.

1. Interlock loop open
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. Capture freeze-frame data and scan all modules for U3538, other HVIL codes, and CAN communication faults.
2. Review live data for the loop L signal, if available, to see whether it is consistently high or changes with the fault.
3. With the vehicle powered down under the manufacturer's high-voltage safety procedure, inspect loop L connectors and wiring for an unseated plug, broken wire, or damaged terminal.
4. Have a qualified technician check loop L continuity and signal voltage using the manufacturer's procedure; avoid probing high-voltage components.
5. If the loop L circuit tests normally, investigate gateway routing and CAN network termination for related communication faults.

Common fixes

• Reconnect a loose loop L interlock connector.
• Repair an open or damaged loop L wire or terminal.
• Replace a confirmed faulty loop L interlock connector or component.
• Repair verified gateway routing or CAN termination issues if the loop circuit is sound.

Can I keep driving?

Avoid driving if the high-voltage warning is active or the vehicle enters limp mode or shuts down, since the interlock may disable propulsion. Do not handle high-voltage connectors yourself.