U3545: High Voltage System Interlock Circuit P

What it means

Generic fault on HVIL loop P. 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 HVIL checks whether high-voltage connectors and covers are secured before operation. The module reports a general fault on loop P; this code alone does not identify whether the cause is an incompletely mated connector, wiring problem, or network communication issue.

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. Save freeze-frame data and scan all modules for loop P, other HVIL, gateway, and CAN codes to see whether the fault is local or network-wide.
2. Check live data for loop P status and note when the fault is present or whether it comes and goes.
3. With the high-voltage system safely disabled by the manufacturer's procedure, inspect accessible loop P connectors for incomplete mating, damaged locks, corrosion, or contamination.
4. Have a qualified technician inspect loop P wiring and test continuity against the manufacturer's specification.
5. If loop P circuit checks pass, use related network codes and measurements to assess gateway routing and CAN termination.

Common fixes

• Fully seat and secure a loose loop P connector.
• Repair damaged loop P wiring or connector terminals.
• Correct gateway routing if diagnosis confirms messages are being sent incorrectly.
• Repair CAN termination only if testing confirms it is out of specification.

Can I keep driving?

Avoid driving if the vehicle enters limp mode, shows a high-voltage warning, or shuts down, as the loop P fault can affect high-voltage operation. Do not disconnect or probe high-voltage components yourself.