U3528: High Voltage System Interlock Circuit G High

HVIL loop G voltage above expected range. The interlock is a low-voltage signal loop routed through the HV connectors and covers; the monitoring module drives a current or signal through it and opens the HV contactors, or refuses to close them, when the loop is broken or out of range, so that no HV connection can be opened while live.

Symptoms

• Vehicle will not switch to ready mode or the HV system shuts down
• High-voltage system warning in the instrument cluster
• Charging may be blocked

Most likely causes

• Interlock loop open
• HV connector, service disconnect or cover switch not fully seated
• Damaged interlock wiring or corroded terminal in the loop
• Fault in the module that drives and evaluates the interlock loop

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. Leave any high-voltage measurements to a specialized repair shop

Good to know

• Repair difficulty: hard
• It can trigger limp mode.

What each character of U3528 means

• U: Communication network
• 3: Generic code: same on every make
• 5: Subsystem depends on the code range
• 28: Specific fault in that system

Frequently asked questions

Can I keep driving with code U3528?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code U3528?

The most common causes are: interlock loop open; hV connector, service disconnect or cover switch not fully seated; damaged interlock wiring or corroded terminal in the loop.

Related codes

• U3524High Voltage System Interlock Circuit F High
• U352CHigh Voltage System Interlock Circuit H High
• U3520High Voltage System Interlock Circuit E High
• U3530High Voltage System Interlock Circuit J High
• U351CHigh Voltage System Interlock Circuit D High
• U3534High Voltage System Interlock Circuit K High
• U3518High Voltage System Interlock Circuit C High
• U3538High Voltage System Interlock Circuit L High

Sources

• github.com: dtc database
• en.wikipedia.org: Battery management system
• law.cornell.edu: 13 CCR 1968.2
• ti.com: tidud43a

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.