Loose or improperly seated high-voltage connector; Damaged or corroded interlock circuit wiring; Faulty interlock switch inside a high-voltage component; Water intrusion or contamination in a high-voltage connector; Failed high-voltage battery pack interlock circuit; Control module software error or internal fault

DTC codes / U35xx · Network communication / U352B

U352BHigh Voltage System Interlock Circuit H Low

Q: What does code U352B mean?

High Voltage System Interlock Circuit H Low. U352B indicates that the high-voltage system interlock loop for circuit H has been detected as having a low voltage condition, meaning the safety circuit that ensures high-voltage connectors are properly seated is not receiving the expected voltage. The vehicle's control module monitors this interlock circuit and sets the code when the voltage falls below the manufacturer's specified threshold, often due to a poor connection or damaged wiring.

U352B indicates that the high-voltage system interlock loop for circuit H has been detected as having a low voltage condition, meaning the safety circuit that ensures high-voltage connectors are properly seated is not receiving the expected voltage. The vehicle's control module monitors this interlock circuit and sets the code when the voltage falls below the manufacturer's specified threshold, often due to a poor connection or damaged wiring.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork communication

Symptoms you may notice

High-voltage system warning light illuminated on the dashboard
Vehicle may refuse to start or enter 'ready' mode
Reduced power or limited operation mode
Often no symptoms besides the warning light
Inability to charge the high-voltage battery (in plug-in vehicles)
Audible alert or message indicating a high-voltage fault

Common causes, most likely first

Loose or improperly seated high-voltage connector
Damaged or corroded interlock circuit wiring
Faulty interlock switch inside a high-voltage component
Water intrusion or contamination in a high-voltage connector
Failed high-voltage battery pack interlock circuit
Control module software error or internal fault

How to diagnose and fix it

Perform a visual inspection of all high-voltage connectors for proper seating and damage
Check for technical service bulletins (TSBs) related to the interlock circuit
Use a scan tool to monitor interlock circuit voltage and compare to specifications
Test continuity and resistance of the interlock circuit wiring
Inspect and clean connector terminals, then apply dielectric grease if specified
Replace faulty interlock switch or high-voltage component as needed
Clear codes and verify repair with a test drive

Interlock Circuit Low Voltage Pitfalls

A common oversight is assuming the high-voltage battery is at fault when the issue is simply a partially unseated connector that was disturbed during previous service.
The interlock circuit often uses a low-voltage loop that can be checked with a multimeter, but the high-voltage system must be powered down and verified dead before any physical inspection.
Some vehicles set this code intermittently due to vibration causing a marginal connection, so a wiggle test of connectors while monitoring live data can reveal the problem.
After any high-voltage component replacement, the interlock circuit may need to be reset or relearned with a scan tool, and skipping this step can cause a repeat code.
This code does not always indicate a hard failure; it can be set by a temporary voltage drop during cranking or a low 12-volt battery, so check the auxiliary battery first.

Can I keep driving with U352B?

Do not continue driving with this code present, as the high-voltage system may be compromised and safety systems could be disabled. Have the vehicle inspected by a qualified high-voltage technician before further use.

Tools that help

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