U3533: High Voltage System Interlock Circuit K Low

What it means

HVIL loop K 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

The high-voltage interlock loop (HVIL) K monitors continuity through part of the high-voltage system. This code sets when the loop K signal falls below its expected range, which can indicate a wire shorted to ground or another condition pulling the monitored signal 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. Capture freeze-frame data and scan all modules for related HVIL or communication faults, noting whether loop K is the only circuit reported.
2. Check live data for the loop K signal or status to confirm it is low while the fault is active.
3. With the high-voltage system made safe under the manufacturer's procedure, inspect accessible loop K wiring for chafed insulation, pinching, or contact with ground.
4. Have a qualified technician test loop K for a short to ground using the manufacturer's circuit test procedure.
5. If loop K has no short, investigate gateway message routing and CAN termination against manufacturer specifications.

Common fixes

• Repair chafed loop K wiring that is shorted to ground.
• Repair damaged terminals or secure a faulty loop K connector.
• Correct a confirmed gateway routing or configuration fault.
• Repair a CAN termination issue if testing shows it is outside the manufacturer's specification.

Can I keep driving?

A low loop K signal can lead to high-voltage shutdown or limp mode. Do not continue driving if power is reduced or high-voltage warnings appear, and have a qualified technician inspect the circuit.