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DTC codes / U35xx · Network communication / U352C

U352CHigh Voltage System Interlock Circuit H High

U352C indicates that the high-voltage interlock loop for circuit H has reported a voltage above the expected threshold, which the vehicle's control module interprets as a potential break or fault in the safety circuit. The interlock is a low-current loop that runs through high-voltage connectors and components; when its voltage goes high, the module suspects the loop is open or has excessive resistance, and it may disable the high-voltage system to prevent shock hazards.

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 caution indicator
  • The vehicle may refuse to start or enter 'Ready' mode, leaving it inoperative
  • Reduced power or a forced limp-home mode if the vehicle does drive
  • The high-voltage contactors may open, cutting power to the traction motor
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Other high-voltage related codes stored in the battery energy control module or power electronics

Common causes, most likely first

  1. A loose, corroded, or unseated high-voltage connector on the interlock circuit H path
  2. Damaged wiring harness or chafed interlock wire causing an open circuit or high resistance
  3. Failed interlock switch inside a high-voltage component such as the battery pack, inverter, or service disconnect
  4. Water intrusion or contamination in a high-voltage connector causing increased resistance
  5. A faulty control module that misreads the interlock voltage, though this is less common
  6. Aftermarket or improper repair that bypassed or damaged the interlock loop

How to diagnose and fix it

  1. Inspect all high-voltage connectors for proper seating, corrosion, or damage, and reseat any suspect connector
  2. Check the interlock circuit wiring for continuity and resistance using a digital multimeter, following the manufacturer's service information
  3. Test the interlock switch or loop at each high-voltage component to isolate the open or high-resistance section
  4. Repair or replace damaged wiring, pins, or connectors in the interlock circuit H path
  5. If a component's internal interlock switch has failed, replace that component according to service procedures
  6. Clear the code and perform a road test to verify the repair, ensuring the high-voltage system operates normally

Interlock faults that fool even seasoned techs

  • A common oversight is assuming the high-voltage battery is at fault when the real problem is a partially unseated connector at the inverter or service disconnect, which can set U352C without any visible damage.
  • The interlock loop often carries a low-voltage pilot signal, so a high voltage reading on circuit H can be caused by a poor ground reference rather than a true open circuit, leading to misdiagnosis of the control module.
  • Intermittent U352C codes that appear only over bumps or in wet weather frequently trace to chafed wiring hidden behind interior trim or under the vehicle, not to a failed high-voltage component.
  • Some vehicles set U352C as a companion code when the 12-volt battery is weak or the charging system is faulty, because low system voltage can distort the interlock signal, so always verify 12-volt power and grounds first.
  • Replacing a high-voltage component without performing the manufacturer's interlock learn or initialization procedure can leave U352C stored even after a correct repair, so follow service information closely.

Can I keep driving with U352C?

Do not continue driving with U352C active, because the vehicle may disable the high-voltage system unexpectedly or refuse to start, and an interlock fault can indicate a potential shock hazard. Have the vehicle inspected by a qualified high-voltage technician before further use.

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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