U352C: High Voltage System Interlock Circuit H High

What it means

HVIL loop H 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

The high-voltage interlock loop (HVIL) H monitors continuity through part of the high-voltage system. This code sets when its monitored signal is higher than expected; an open in loop H can leave the circuit in that state and may cause the system to disable high-voltage operation.

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. Record freeze-frame data and scan every module for associated interlock and communication faults to establish whether the issue centers on loop H.
2. Check live data for the HVIL H status and confirm whether the signal is high or reports an open condition while the fault is current.
3. With the vehicle's high-voltage system made safe by a qualified technician, visually inspect accessible loop H connectors for incomplete mating and wiring for breaks or pulled terminals.
4. Have a qualified technician test loop H continuity and open-circuit behavior according to the manufacturer's procedure.
5. If the loop itself passes, check gateway routing and CAN termination against the manufacturer's specifications.

Common fixes

• Fully seat a loose loop H HV connector following the vehicle maker's safety procedure.
• Repair an open or broken section of loop H wiring.
• Replace damaged connector terminals or repair a connector that cannot maintain continuity.
• Correct confirmed gateway routing or CAN termination faults.

Can I keep driving?

An open or high HVIL H signal may cause the vehicle to disable high-voltage functions or enter limp mode. Avoid continued driving if power or propulsion is affected, and have a qualified technician inspect the system before relying on the vehicle.