U3522: High Voltage System Interlock Circuit F Performance

What it means

HVIL loop F timing/pattern does not match expected behavior. 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 F checks that monitored connectors and components remain securely connected. This performance code means the loop F signal pattern or behavior does not match what the control module expects, often pointing to an intermittent connection rather than a steady high or low reading.

Common causes

Most likely first.

1. Intermittent contact in HV connector
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 check whether U3522 appears with vibration, temperature changes, or other interlock and communication faults.
2. With the vehicle powered down according to manufacturer instructions, inspect accessible loop F connectors and harness sections for looseness, chafing, corrosion, or signs of intermittent contact.
3. Use scan-tool live data to watch loop F status while checking for repeatable changes under approved conditions; do not disturb high-voltage connectors while energized.
4. Have a qualified high-voltage technician test loop F connectors and circuit behavior using the manufacturer's procedures and specifications.
5. If the loop signal is stable during testing, inspect gateway routing and CAN termination for intermittent network faults using vehicle-specific wiring information.

Common fixes

• Reseat a loose loop F connector using the manufacturer's procedure.
• Repair chafed or corroded loop F wiring and terminals.
• Replace a connector or interlock component confirmed to have intermittent contact.
• Repair a verified intermittent gateway or CAN termination fault.

Can I keep driving?

Intermittent interlock faults can cause sudden reduced power or shutdown, so avoid driving if warnings or drivability changes occur. A qualified high-voltage technician should inspect the vehicle before normal use.