U3536

What it means

U3536 means the control unit monitoring the high voltage system interlock loop (a low-voltage safety circuit running through the high voltage connectors, covers and service disconnect) has found that circuit L is not performing as expected. The signal may be intermittent, out of range or not the expected pattern, even if the loop is not fully open. The control unit may then stop the high voltage contactors closing or open them to protect people and equipment. Which loop 'L' refers to and which components are in it depends on the model.

Symptoms

• Hybrid or electric system warning lamp or malfunction message on the dash
• Vehicle will not go to Ready or will not start
• Reduced power or limp-home mode
• Sudden loss of drive while moving
• Charging will not start or stops part way through
• Other high voltage or network fault codes stored alongside

Possible causes

• Loose, damaged, corroded or partly unseated interlock connector on a high voltage componentlikely
• Damaged or chafed interlock wiring causing high resistance, intermittent open circuit or shortlikely
• High voltage connector, cover or service disconnect not fully seated after earlier worklikely
• Water ingress or contamination in a connector on the interlock looppossible
• Faulty interlock switch or pins within a high voltage component such as the battery, inverter, charger or compressorpossible
• Fault in the control unit generating or monitoring the interlock signal, or an outdated calibration where the manufacturer has issued an updaterare

How to diagnose

1. Only qualified, high voltage trained staff should work on this system. Follow the manufacturer's procedure for isolating and proving the system dead before touching any high voltage parts.
2. Read all stored and pending codes with freeze frame data, noting whether the fault is current or intermittent and whether other high voltage or network codes are present.
3. Check the service data, if available, for the interlock loop status and which control unit set the code.
4. Visually inspect the high voltage connectors, covers, service disconnect and interlock plugs on the affected loop for correct seating, locking tabs, damage, corrosion and moisture.
5. Using the wiring diagram for that model, identify the components in loop L and inspect the harness for chafing, pinching, previous repair damage or water entry.
6. With the system isolated, test the interlock loop for continuity, resistance and shorts to earth or supply as specified by the manufacturer, flexing the harness to find intermittent faults.
7. Check the interlock switches or bridging pins inside each component on the loop against the manufacturer's specification.
8. Check for technical bulletins or calibration updates relevant to the model before condemning a control unit.

How to fix

• Reseat, clean or replace damaged or corroded interlock and high voltage connectors and ensure all locks are fully engaged.
• Repair or replace the damaged interlock wiring section using the manufacturer's approved method.
• Dry out and seal connectors that have had water ingress, and replace seals or terminals that are damaged.
• Replace the high voltage component or its interlock switch if the fault is confirmed inside it.
• Refit any covers or the service disconnect correctly, then clear the code and road test to confirm it does not return.
• Update the control unit calibration or replace the unit only if it is confirmed faulty or a known calibration fault applies.

Can I keep driving?

Nearby codes

• U3535GenericHigh Voltage System Interlock Circuit L
• U3537GenericHigh Voltage System Interlock Circuit L Low