U3514: High Voltage System Interlock Circuit B High

What it means

HVIL loop B voltage above expected range — open or short to power. 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 checks whether monitored connectors are properly engaged. U3514 indicates a loop B signal above its expected range, which can result from an open loop, an unmated connector, or a short to power; the high-voltage system may be disabled for safety.

Common causes

Most likely first.

1. Interlock loop open (connector unmated)
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 for related loop B, interlock, and communication codes to see whether the signal fault is isolated.
2. Using the manufacturer's high-voltage safety procedure, inspect accessible loop B connectors for incomplete seating and wiring for breaks, damage, or contact with a power source.
3. Check scan-tool loop B status and compare it with other interlock loops where available.
4. Have a qualified technician test loop B for an open circuit or short to power against the manufacturer's specification with the high-voltage system safely isolated.
5. If the loop circuit checks out, examine module inputs and gateway communication using vehicle-specific service information.

Common fixes

• Fully seat a loose loop B connector using the manufacturer's high-voltage procedure.
• Repair an open or damaged loop B wire or a short to power.
• Replace a connector or interlock component confirmed faulty by testing.
• Repair a confirmed module or gateway fault after the circuit is verified.

Can I keep driving?

Avoid driving if the vehicle shows a high-voltage warning, loses propulsion, or enters a restricted mode; loop B may be preventing safe high-voltage operation. Do not handle high-voltage connectors yourself; arrange qualified service.