U3521
High Voltage System Interlock Circuit F
U3521 is an OBD-II diagnostic trouble code meaning: High Voltage System Interlock Circuit F. Common causes: open circuit in the locking circuit, short circuit. Estimated repair cost: $56–222.
Symptoms
- Check Engine light comes on
- Reduced vehicle power
- Complete loss of traction (in some cases)
- Error message on display
- Inability to start the engine (for hybrids)
Causes
- Open circuit in the locking circuit
- Short circuit
- Lock sensor malfunction
- Problems with high voltage relay
- Control module malfunction
How to Fix
- Check the integrity of the locking circuit
- Check connections and connectors
- Test blocking sensors
- Check the operation of the high-voltage relay
- Diagnose the control module
- Repair only from an authorized dealer
Related codes
Error U3521 by Vehicle Brand
FAQ
What does the U3521 code mean?
U3521 is an OBD-II diagnostic trouble code that indicates: High Voltage System Interlock Circuit F
What causes a U3521 error code?
The most common causes of U3521 include: Open circuit in the locking circuit; Short circuit; Lock sensor malfunction; Problems with high voltage relay.
How do I fix a U3521 diagnostic trouble code?
To fix U3521: Check the integrity of the locking circuit. Check connections and connectors. Test blocking sensors. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with U3521?
Do not drive — repair immediately
How much does it cost to fix U3521?
The estimated repair cost for U3521 is $56–222. Actual cost depends on your vehicle, location, and labor rates.
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