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DTC codes / U35xx · Network communication / U3526

U3526High Voltage System Interlock Circuit G Performance

U3526 indicates that the high-voltage interlock loop for circuit G has reported a performance fault, typically a voltage reading outside the expected range, to the vehicle's control module. The interlock is a safety circuit that confirms all high-voltage connectors and covers are properly seated before allowing the high-voltage system to energize. The computer detected an abnormal voltage signature on the interlock loop for circuit G, which may prevent the high-voltage system from activating or may trigger a shutdown.

SystemNetwork
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaNetwork communication

Symptoms you may notice

  • Illumination of the high-voltage system warning light or a master warning indicator on the dashboard.
  • The vehicle may refuse to start or enter 'Ready' mode, leaving the high-voltage system disabled.
  • A message on the driver information display stating that the high-voltage system is unavailable or that a service interlock is required.
  • Possible reduction in power or limited operation if the vehicle is already running when the fault occurs.
  • Often no symptoms besides the warning light, especially if the fault is intermittent and the interlock circuit momentarily drops out.
  • In some cases, the vehicle may stall or shut down while driving if the interlock circuit is interrupted.

Common causes, most likely first

  1. A high-voltage connector that is not fully latched or has a damaged interlock pin, causing a poor connection in circuit G.
  2. Corrosion or water intrusion at a high-voltage connector or interlock switch, leading to increased resistance or an open circuit.
  3. A faulty high-voltage interlock switch or sensor integrated into a connector or service disconnect plug.
  4. Wiring damage such as a chafed, pinched, or broken wire in the interlock loop for circuit G.
  5. A malfunctioning control module that monitors the interlock circuit, such as the battery energy control module or vehicle control unit.
  6. Aftermarket accessories or improper previous repairs that disturbed the high-voltage interlock circuit.
  7. A failed high-voltage component (e.g., battery pack, inverter, or motor) whose internal interlock circuit is open or shorted.

How to diagnose and fix it

  1. Perform a visual inspection of all high-voltage connectors and service disconnect plugs, checking for loose latches, corrosion, or damaged pins, and reseat any suspect connectors.
  2. Use a scan tool to read the specific fault data and freeze-frame information for U3526, and check for related codes in other modules to narrow the circuit.
  3. Consult the vehicle-specific service information for the high-voltage interlock circuit G to identify the exact connector and pin locations, then measure resistance and voltage on the interlock loop with a digital multimeter.
  4. Perform a wiggle test on the harness and connectors while monitoring the interlock circuit voltage or resistance to detect intermittent faults.
  5. If the interlock circuit includes a service disconnect plug or manual disconnect, inspect the internal switch and replace it if faulty.
  6. Repair or replace any damaged wiring, pins, or connectors in the interlock circuit, following high-voltage safety procedures and using proper terminal repair tools.
  7. After repairs, clear the codes and verify that the high-voltage system powers up correctly and that U3526 does not return during a test drive.

Interlock Faults That Fool Even Seasoned Techs

  • A common oversight is assuming the interlock switch itself has failed when the real problem is a partially unseated high-voltage connector that looks latched but is not fully engaged.
  • The interlock circuit is a low-voltage loop, so a simple continuity check can miss intermittent high-resistance faults that only appear under vibration or temperature change.
  • Some vehicles set U3526 when the 12-volt battery is weak or during voltage spikes, so always verify system voltage and charging before condemning high-voltage components.
  • Aftermarket alarm or remote-start installations that tap into wiring near high-voltage connectors can disturb the interlock loop and set this code.
  • A high-voltage interlock fault does not always mean the high-voltage battery is defective; the issue is frequently in the connector or wiring, not the pack itself.

Can I keep driving with U3526?

Do not continue driving if the high-voltage system warning is active, because the vehicle may lose power unexpectedly or refuse to restart. Have the vehicle inspected by a qualified high-voltage technician before attempting further operation.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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