U351A: High Voltage System Interlock Circuit D Performance

What it means

HVIL loop D timing/pattern does not match expected 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

The high-voltage interlock loop D is monitored for a safety signal pattern over time. This code sets when the pattern or timing from loop D does not match what the control module expects, which may point to intermittent contact at a connector. The fault can also interrupt communication with dependent systems.

Common causes

Most likely first.

1. Intermittent contact in HV connector
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 D, gateway, and CAN communication faults to establish whether the fault is intermittent or widespread.
2. Observe loop D status in live data while the vehicle is stationary and note any changes or dropouts.
3. With the high-voltage system safely disabled according to the vehicle's service procedure, inspect accessible loop D connectors and wiring for looseness, corrosion, abrasion, or damage.
4. Have a qualified technician test loop D continuity and signal timing against the manufacturer's specification while checking for intermittent contact.
5. If multiple modules report communication faults, test gateway routing and CAN termination according to the vehicle's diagnostic procedure.

Common fixes

• Secure or repair an intermittent loop D connector.
• Repair damaged loop D wiring or terminals causing a signal dropout.
• Correct gateway routing or configuration if testing confirms a gateway fault.
• Repair or replace a CAN terminating resistor if it is outside the manufacturer's specification.

Can I keep driving?

Avoid driving if warnings are accompanied by limp mode, reduced power, or shutdown; arrange safe diagnosis. Intermittent loop D faults can disable high-voltage functions unexpectedly, and high-voltage connectors require qualified handling.