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U3528 — High Voltage System Interlock Circuit G High

Manufacturer-specificNetwork / communication

U3528 indicates the high-voltage (HV) interlock loop segment labeled Circuit G is reporting a higher-than-expected voltage, which the control module interprets as an open loop or a short to voltage. The interlock is a low-voltage safety circuit that runs through HV connectors and components; if continuity is lost, the system disables or limits HV operation to protect occupants and technicians.

Symptoms

What causes it — most likely first

1. Open or damaged Circuit G interlock wiring/connector

A pinched, chafed, corroded, or poorly seated connector in the Circuit G interlock path breaks continuity, causing the control module to see a high-voltage state.

2. Faulty interlock switch or service disconnect in Circuit G

A service plug, battery disconnect, junction box, or HV component interlock switch may be stuck open or internally failed, opening the loop even when connectors appear seated.

3. Short to voltage in the interlock signal wire

The Circuit G signal wire may be rubbed through and touching a higher-voltage source, pulling the monitored circuit high and setting the code.

4. High-voltage component internal interlock fault

An HV component on Circuit G—such as a battery module, inverter, compressor, or heater—may have an internal interlock switch or circuit failure that interrupts the loop.

5. Control module sensing/input circuit failure

The hybrid/powertrain or battery control module can misread the interlock input if its internal sensing circuit is damaged, but this is uncommon and should be considered only after wiring and switches test good.

How it's diagnosed

  1. Retrieve freeze-frame data and review all stored HV-interlock-related codes to identify which loop segment is affected.
  2. Inspect the Circuit G interlock connectors, pins, and wiring for corrosion, damage, looseness, or evidence of overheating; repair or secure as needed.
  3. Perform continuity and resistance checks of the Circuit G interlock loop through each connector and component; identify where the loop opens.
  4. Check the interlock signal voltage and test for a short to power or ground; compare readings to factory specifications.
  5. Verify each interlock switch and service disconnect operates correctly; if wiring and switches are good, evaluate the control module input before replacing any module.

Code facts & related codes

SystemNetwork / communication
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesU3520 — High Voltage System Interlock Circuit U3521 — High Voltage System Interlock Circuit U3522 — High Voltage System Interlock Circuit U3523 — High Voltage System Interlock Circuit U3524 — High Voltage System Interlock Circuit U3525 — High Voltage System Interlock Circuit

Frequently asked

Is it safe to drive with U3528 stored?

It is usually not advisable. A high-voltage interlock fault can cause the vehicle to enter a reduced-power or disabled state, and it indicates a potential HV safety-loop integrity problem that should be diagnosed before driving.

Does U3528 mean the high-voltage battery is failing?

Usually not. This code concerns the low-voltage safety interlock circuit, not the HV battery cells themselves. Most cases are caused by wiring, connector, or switch faults in the interlock loop.

Should I replace the PCM or hybrid control module for U3528?

Rarely. The failed component itself—wiring, connector, or interlock switch—is the most common cause. A control module should only be suspected after the entire Circuit G loop and all switches have been verified to be in good condition.

What does 'Circuit G High' specifically mean?

It means the control module sees a high voltage on the monitored interlock input for Circuit G. That typically signals an open interlock loop or a short to a higher voltage source in that specific segment.