U3534: High Voltage System Interlock Circuit K High

What it means

HVIL loop K 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 K is a low-voltage safety circuit that lets the vehicle detect whether high-voltage connectors and covers are secure. The control module monitors the loop K signal and sets this code when its voltage is higher than the expected range, which can indicate an open loop. A gateway or CAN fault can also disrupt related reports, so check for communication codes alongside this circuit fault.

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. Use a scan tool to save freeze-frame data and check which modules report U3534 or other communication faults before clearing codes.
2. Review live data for the HVIL loop K status or voltage, if available, and note whether it remains high or changes intermittently.
3. With the vehicle powered down according to the manufacturer's high-voltage safety procedure, visually inspect loop K connectors, interlock wiring, and connector seating for an open circuit or damage.
4. Have a qualified technician test continuity and the signal path of loop K using the manufacturer's procedure; do not probe or disconnect high-voltage components casually.
5. If loop K tests correctly, investigate gateway message routing and CAN network termination against the manufacturer's diagnostic procedure.

Common fixes

• Secure a loose low-voltage interlock connector in loop K.
• Repair damaged loop K interlock wiring or terminals.
• Replace a failed loop K connector or interlock component after confirming the open circuit.
• Repair gateway or CAN termination faults if loop K itself tests correctly.

Can I keep driving?

Avoid driving if the vehicle shows a high-voltage system warning, loses propulsion, or enters limp mode; the interlock fault can cause the system to shut down. Arrange diagnosis promptly, and do not handle high-voltage connectors yourself.