U3537: High Voltage System Interlock Circuit L Low

What it means

HVIL loop L voltage below 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 confirms high-voltage connectors and covers are secure. The control module sets U3537 when loop L voltage falls below its expected range, which can result from a wire shorted to ground. Related gateway or CAN faults may affect communication about the circuit but do not establish that the loop voltage itself is low.

Common causes

Most likely first.

1. Interlock wire shorted to ground
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 every module for U3537 and related communication codes before clearing faults.
2. Check live data for loop L voltage or status, if available, and confirm whether the signal is reported low when the code is active.
3. With the vehicle safely powered down per the manufacturer's high-voltage procedure, inspect loop L low-voltage wiring for crushed insulation, grounding, corrosion, or connector damage.
4. Have a qualified technician test the loop L signal wire for a short to ground and verify continuity using the manufacturer's specifications and procedure.
5. If the wiring passes, diagnose gateway routing and CAN termination only where other codes or data point to a network problem.

Common fixes

• Repair loop L wiring that is shorted to ground.
• Clean or replace corroded loop L terminals causing a low signal.
• Replace a confirmed faulty loop L interlock component.
• Correct a verified gateway or CAN network fault if the loop L circuit tests properly.

Can I keep driving?

Do not continue driving if the vehicle reports a high-voltage system warning, loses power, or shuts down; the interlock fault may disable propulsion. Avoid touching high-voltage parts and arrange prompt diagnosis.