U353F

What it means

U353F means a control unit has detected a low signal on high voltage system interlock circuit N. The interlock is a low-voltage safety loop that runs through high voltage connectors, covers and components to confirm they are fitted and secure before the high voltage system is enabled. The module saw the loop voltage or signal below its expected range, which can point to a short to ground or a fault in the loop. Which loop 'N' refers to depends on the vehicle and must be checked in the manufacturer information.

Symptoms

• Hybrid or EV warning lamp or high voltage system fault message on the dashboard
• Vehicle will not go into READY mode or will not start
• Reduced power or limp mode while driving
• High voltage system shuts down unexpectedly
• Charging will not start or stops early on plug-in models
• Other related U-codes or high voltage isolation codes stored

Possible causes

• Interlock wiring chafed or shorted to ground in the low-voltage looplikely
• Damaged, corroded or water-affected interlock connector or terminals at a high voltage componentlikely
• High voltage connector, service disconnect or cover not fully seated after recent work or damagepossible
• Internal fault in a high voltage component's interlock switch or circuit (such as inverter, charger, battery pack or compressor), model dependentpossible
• Fault in the control unit monitoring the loop or its power and ground supplyrare
• Collision or underbody damage affecting the interlock harnessrare

How to diagnose

1. Read all stored codes and freeze frame data, noting whether the fault is current or history and which modules have set related codes.
2. Check the manufacturer information to identify which interlock loop circuit N is and which components and connectors it passes through.
3. Only qualified high voltage technicians should carry on: follow the manufacturer's procedure to make the system safe and prove it dead before touching any high voltage component.
4. Visually inspect the interlock harness and connectors along the loop for chafing, crush damage, corrosion, water ingress, bent or pushed-back pins and incomplete locking.
5. Check that all high voltage connectors, covers and the service disconnect are fully fitted and latched.
6. With the system made safe, test the interlock loop for continuity and for a short to ground using the manufacturer's specified values.
7. Isolate sections of the loop by disconnecting one component at a time, as the procedure allows, to find which section causes the low reading.
8. Clear the code after repair and road test, then recheck that it does not return.

How to fix

• Repair or replace the damaged section of interlock wiring, using the approved repair method.
• Clean, repair or replace corroded or damaged interlock connectors and terminals.
• Refit and correctly latch any loose high voltage connector, cover or service disconnect.
• Replace the high voltage component with the internal interlock fault, once confirmed by testing.
• Repair or replace the monitoring control unit only after the wiring and components are proven good.

Can I keep driving?

Nearby codes

• U353EGenericHigh Voltage System Interlock Circuit N Performance
• U3540GenericHigh Voltage System Interlock Circuit N High