U3517

What it means

U3517 means the high voltage system interlock circuit 'C' is reading a low signal. The interlock (HVIL) is a low-voltage loop running through high voltage connectors, covers and components to confirm they are all secure before the high voltage system is energised. The control unit monitoring the loop saw its voltage below the expected range, which can mean a short to ground or a loop fault. Which loop 'C' refers to, and where it runs, depends on the vehicle, so check the model-specific information.

Symptoms

• Hybrid or EV system warning light or message on the dashboard
• Vehicle will not enter ready mode or will not start
• Loss of drive power or limp-home mode
• High voltage system shuts down while driving
• Charging will not start or is interrupted
• Other high voltage or network fault codes stored alongside

Possible causes

• Interlock wiring chafed or shorted to ground, or damaged by water ingresslikely
• Corroded, bent, pushed-out or poorly seated pins in an interlock connectorlikely
• High voltage connector, service disconnect or cover not fully latched or refitted incorrectly after earlier workpossible
• Faulty interlock switch or bridge within a high voltage component such as the battery, inverter, charger or compressorpossible
• Fault in the monitoring control unit's interlock circuit or its supply or groundrare
• Accident or underbody damage to high voltage harness or componentsrare

How to diagnose

1. Read all stored and pending codes and freeze frame data, noting whether the fault is current or intermittent and which other codes appear with it.
2. Check for service bulletins and the manufacturer's wiring diagram to identify which components and connectors are on interlock circuit C for this model.
3. Make sure the high voltage system is isolated and proven dead by a suitably trained technician, following the manufacturer's safety procedure, before touching any orange high voltage connectors or components.
4. Visually inspect the interlock loop wiring, connectors, covers and the service disconnect for damage, water, corrosion, loose latches or signs of recent work.
5. Inspect the connector pins for spread, corrosion or push-back, and check that each connector locks fully.
6. With the loop disconnected and the system isolated, test the interlock wiring for a short to ground and for continuity against the wiring diagram.
7. Check the interlock switches or bridges in each component on the loop for correct resistance or continuity as specified.
8. Check the monitoring control unit's supply, ground and interlock output, and only suspect the unit once wiring and components are proven good.

How to fix

• Repair or replace damaged interlock wiring, and seal against water ingress.
• Clean, repair or replace corroded or damaged interlock connector terminals and housings.
• Refit and fully latch the high voltage connectors, covers and service disconnect correctly.
• Replace the faulty high voltage component or its interlock switch, as the manufacturer permits.
• Replace or reprogram the control unit only if testing proves it faulty, using the manufacturer's procedure, then clear the codes and confirm they do not return.

Can I keep driving?

Nearby codes

• U3516GenericHigh Voltage System Interlock Circuit C Performance
• U3518GenericHigh Voltage System Interlock Circuit C High