U3511: High Voltage System Interlock Circuit B

What it means

Generic fault on the second high-voltage interlock loop (HVIL) circuit. The interlock detects whether HV connectors are properly mated; an open loop forces the HV system into a safe state.

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 that monitored high-voltage connectors are properly seated so the vehicle can keep the high-voltage system in its permitted state. U3511 indicates a general fault in loop B, such as an open loop from an unmated connector or damaged pilot contact, and the system may disable high-voltage operation.

Common causes

Most likely first.

1. HV connector not fully mated
2. Interlock pilot pin damaged
3. Gateway module routing CAN messages incorrectly

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 hybrid or electric vehicle modules for related interlock, isolation, and communication codes.
2. Using only the manufacturer's high-voltage safety procedure, inspect the accessible loop B connectors and harness for an unseated connection or visible damage.
3. Check whether the scan tool reports loop B as open and compare its status with the other interlock loops where supported.
4. Have a qualified technician test loop B continuity and its pilot-pin connections with the high-voltage system safely isolated as specified by the manufacturer.
5. If loop B wiring and connector tests pass, investigate related module or gateway communication faults using vehicle-specific service information.

Common fixes

• Correct a visibly loose loop B connector only by the manufacturer's high-voltage procedure.
• Repair damaged low-voltage interlock wiring or a faulty pilot-pin connection using approved parts and methods.
• Replace a connector or interlock component confirmed faulty by testing.
• Repair a confirmed module or gateway communication fault after loop B checks.

Can I keep driving?

Do not touch or unplug high-voltage connectors; the vehicle may disable propulsion or enter a restricted mode, and high-voltage components can be hazardous. If the vehicle has a high-voltage warning, will not operate normally, or shows shutdown symptoms, stop when safe and have it handled by a qualified high-voltage technician.