U3533

What it means

U3533 is a generic code for a fault in the high voltage interlock loop, labelled circuit K, where the signal is reading low. The interlock is a low-voltage safety loop that runs through high voltage connectors, covers and components so the control unit knows the system is closed and safe to energise. The control unit saw the loop voltage or signal sitting lower than expected, which suggests a short to ground or a fault in the loop. Which part of the vehicle circuit K covers depends on the model, so check the manufacturer wiring information.

Symptoms

• Hybrid or electric system warning light 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 or the contactors will not close
• Charging will not start or stops early
• Other communication or high voltage fault codes stored alongside

Possible causes

• Interlock loop wiring chafed or shorted to groundlikely
• Damaged, wet or corroded interlock pins in a high voltage connectorlikely
• Connector or service disconnect not fully seated after recent work or an impactpossible
• Fault inside a high voltage component that is part of circuit K (for example a charger, inverter, battery pack or compressor), depending on modelpossible
• Water ingress or contamination in a connector or component on the looppossible
• Internal fault in the control unit that monitors or drives the interlock looprare

How to diagnose

1. Make sure only a technician trained in high voltage systems does this work, and follow the manufacturer's safe isolation procedure before touching any orange cabling or connectors.
2. Read all stored codes and freeze frame data, noting whether the fault is current or historic and which other units have set related codes.
3. Check for recent repairs, accident damage or water ingress that could have disturbed connectors or wiring on the interlock loop.
4. Look over the interlock loop wiring and connectors for chafing, pinching, corrosion, bent or pushed-back pins, and confirm each connector and cover is fully latched.
5. Use the manufacturer wiring information to find which components and connectors make up circuit K on this model.
6. With the system isolated, test the loop wiring for a short to ground and for continuity, using the specified values.
7. Disconnect the components on the loop one at a time, as the procedure allows, to see whether the short to ground clears and so isolate the faulty section.
8. After repair, clear the code, then confirm it does not return and that the system energises normally.

How to fix

• Repair or replace damaged interlock wiring, with the repair carried out to the manufacturer's method.
• Clean or replace corroded or damaged connectors and terminals, and dry out any water ingress.
• Refit and secure any loose connector, cover or service disconnect so the loop is complete.
• Replace the faulty high voltage component if it is shown to be causing the low signal on the loop.
• Replace or reprogram the controlling unit only if testing shows it is faulty or the manufacturer lists a calibration update for this fault.

Can I keep driving?

Nearby codes

• U3532GenericHigh Voltage System Interlock Circuit K Performance
• U3534GenericHigh Voltage System Interlock Circuit K High