U3515: High Voltage System Interlock Circuit C

What it means

Generic fault on HVIL loop C. See U3511 for general HVIL 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

High-voltage interlock loop C monitors whether its designated high-voltage connectors are engaged so the system can determine whether high-voltage operation is permitted. U3515 indicates a general fault in loop C, such as an open circuit or unseated connector, and may cause the system to restrict or disable propulsion.

Common causes

Most likely first.

1. HV connector not fully mated
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 the vehicle modules for loop C, other interlock, and communication codes to identify the reporting module.
2. Follow the manufacturer's high-voltage safety procedure when inspecting accessible loop C connectors and wiring for poor seating or visible damage.
3. Check scan-tool data for loop C status and compare it with loops B and other available interlock circuits.
4. Have a qualified technician test loop C continuity and connector pilot contacts with the high-voltage system safely isolated according to the manufacturer's procedure.
5. If loop C wiring passes, investigate the related module and gateway communication using vehicle-specific service information.

Common fixes

• Correct a loose loop C connector using the manufacturer's high-voltage procedure.
• Repair damaged loop C wiring or connector terminals.
• Replace an interlock component confirmed faulty by testing.
• Repair a confirmed module or gateway communication fault after verifying loop C.

Can I keep driving?

Do not touch or unplug high-voltage connectors; the vehicle may restrict or disable propulsion, and high-voltage components are hazardous. If a high-voltage warning or operating restriction appears, stop when safe and arrange qualified service.