U352C

What it means

U352C is defined as High Voltage System Interlock Circuit H High. The high voltage interlock loop is a low-voltage signal circuit that runs through high-voltage connectors, covers and components to confirm the system is fully closed and safe. The control unit that monitors the loop saw the signal on circuit 'H' above its expected range. Depending on the design, this can mean a short to voltage, a fault in the loop wiring or a fault in a component in the loop. The exact loop layout and what 'H' refers to vary by manufacturer and model.

Symptoms

• Hybrid or electric system warning light or message on the dashboard
• Car will not go into READY mode or will not start
• Reduced power or limp mode while driving
• High-voltage system shuts down or contactors do not close
• Charging will not start or is interrupted
• Other stored codes for the high voltage battery, inverter or charger

Possible causes

• Loose, corroded or poorly seated interlock connector on a high-voltage component (battery, inverter, charger, compressor or heater)likely
• Damaged, chafed or water-affected interlock wiring, including a short to a voltage supplylikely
• High-voltage connector or service disconnect not fully engaged, or cover or plug left unseated after recent workpossible
• Faulty interlock switch or bridge within a high-voltage componentpossible
• Fault in the monitoring control unit's interlock circuit or its supplyrare
• Outdated or faulty control unit software, where the manufacturer has identified it as a known cause for the modelrare

How to diagnose

1. Treat the high-voltage system as live: only trained staff should work on it, and follow the manufacturer's isolation and safety procedure before touching any high-voltage parts.
2. Read all stored and pending codes and record freeze frame data to see the conditions when the fault set and whether other high-voltage faults appear alongside it.
3. Check for recent work, accident damage or water ingress, and confirm all high-voltage covers, plugs and the service disconnect are fully seated and latched.
4. Visually inspect the interlock connectors and wiring for bent or pushed-back pins, corrosion, moisture, chafing and damage, following the harness path for your model.
5. Use live data, if available, to see the interlock loop status and which component the control unit reports as open or out of range.
6. With the system isolated, use the wiring diagram to test the interlock loop for continuity, short to voltage and short to ground, working section by section.
7. Check the supply and reference voltage to the monitoring control unit and the integrity of its connector.
8. Check for software updates or technical bulletins relevant to the model and fault.

How to fix

• Clean, reseat and properly latch loose or corroded interlock connectors, replacing any with damaged terminals or housings.
• Repair or replace damaged interlock wiring, including any short to voltage, using the manufacturer's approved repair method.
• Refit and secure any high-voltage cover, plug or service disconnect that is not fully engaged.
• Replace a faulty high-voltage component or its interlock switch or bridge, as confirmed by testing.
• Replace the monitoring control unit only if the circuit and supplies are proven good and the unit is confirmed faulty.
• Apply a manufacturer software update if one is available for a known fault, then clear the code and confirm it does not return.

Can I keep driving?

Nearby codes

• U352BGenericHigh Voltage System Interlock Circuit H Low
• U352DGenericHigh Voltage System Interlock Circuit J