U3519

What it means

U3519 means the control unit monitoring the high voltage system interlock has detected a fault on interlock circuit D. The interlock is a low-voltage safety loop that runs through high voltage connectors, covers and components, and confirms they are all connected and secure. If the loop is open, shorted or reads out of range, the system treats it as a possible exposure to high voltage and may open the contactors. Which components sit on circuit D depends on the make, model and system layout.

Symptoms

• High voltage warning light, hybrid or EV system fault message, or general warning light on the dashboard
• Car will not go into ready mode or will not start
• Loss of drive power or reduced power while driving
• High voltage battery contactors not closing, or the car shutting down the high voltage system
• Charging will not start or stops early on a plug-in vehicle

Possible causes

• High voltage connector or interlock plug not fully seated, or its locking latch damaged, on a component in circuit Dlikely
• Open circuit, high resistance or corrosion in interlock wiring or terminals, often after previous repair work or water ingresslikely
• Service disconnect, component cover or inverter or charger lid not refitted correctly after maintenancepossible
• Wiring chafed or shorted to ground or to supply voltage, giving an out-of-range interlock signalpossible
• Fault inside a high voltage component such as the battery pack, inverter, DC-DC converter, charger or compressor that carries the interlock looppossible
• Fault in the monitoring control unit, its interlock driver circuit or its softwarerare

How to diagnose

1. Only trained technicians should work on this. Follow the manufacturer's high voltage safety and isolation procedure before touching any orange high voltage connector or component.
2. Read all stored codes and freeze frame data, noting any related high voltage, contactor or communication faults, and whether the fault is current or historic.
3. Check the wiring diagram for the vehicle to identify which connectors, covers and components are on interlock circuit D.
4. Visually inspect those connectors, locks, covers and the service disconnect for correct seating, damage, moisture, corrosion and signs of recent repair.
5. With the high voltage system isolated and proved dead, check interlock circuit continuity and resistance end to end, and check for shorts to ground or supply voltage, using the manufacturer's values.
6. Check terminal tension and pin condition in the interlock contacts, and look for wiring chafe along the harness route.
7. Use live data, if available, to see the interlock status and work through the loop section by section to find where it opens.
8. If wiring and connectors are good, test the components on the loop and check for software updates applicable to the vehicle before suspecting the control unit.

How to fix

• Reseat and correctly lock any loose high voltage or interlock connector, and refit covers or the service disconnect as specified.
• Repair or replace damaged interlock wiring, terminals or connectors, and clean or seal out moisture and corrosion.
• Replace a high voltage component or its interlock section if the loop fault is found to be inside it.
• Repair the short to ground or supply by replacing the damaged harness section and securing it clear of chafe points.
• Replace or reprogram the monitoring control unit only after the loop and components are proven good, or if the manufacturer lists a software update for this fault.
• Clear the code after repair and road test, confirming that it does not return and that the system reaches ready mode.

Can I keep driving?

Nearby codes

• U3518GenericHigh Voltage System Interlock Circuit C High
• U351AGenericHigh Voltage System Interlock Circuit D Performance