U3513: High Voltage System Interlock Circuit B Low

What it means

HVIL loop B voltage below expected range — short to ground in the interlock wiring. 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 B monitors whether its high-voltage connectors are engaged, allowing the system to enter its permitted operating state. U3513 indicates that loop B's signal is below the expected range, consistent with a short to ground or a related circuit fault; the system may disable high-voltage operation.

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. Record freeze-frame data and scan all high-voltage modules for loop B, isolation, and communication codes before clearing anything.
2. Following the manufacturer's high-voltage safety procedure, inspect accessible loop B wiring and connectors for chafing, crushed insulation, moisture, or poor seating.
3. Check scan-tool data for loop B signal status and compare it with other interlock loops if the vehicle provides that information.
4. Have a qualified technician test loop B for a short to ground and verify its circuit behavior against the manufacturer's specification with the high-voltage system safely isolated.
5. If loop B wiring passes, investigate the reporting module and gateway communication using vehicle-specific service information.

Common fixes

• Repair loop B wiring shorted to ground or chafed against the chassis.
• Correct a damaged or poorly seated loop B connector using the manufacturer's high-voltage procedure.
• Replace an interlock component confirmed faulty by circuit testing.
• Repair a confirmed module or gateway fault after checking the loop.

Can I keep driving?

Do not touch high-voltage components; the system may disable propulsion or enter a restricted state. If a high-voltage warning or loss of drive occurs, stop when safe and arrange qualified high-voltage service.