Damaged or chafed interlock wiring shorted to a higher voltage source; Faulty high-voltage interlock connector or terminal with poor pin tension; Failed high-voltage component (e.g., battery pack, inverter, or motor) internal interlock switch; Corrosion or moisture intrusion in the interlock circuit connector; Control module internal fault misreading the interlock voltage; Aftermarket accessories improperly wired into the high-voltage system

DTC codes / U35xx · Network communication / U353C

U353CHigh Voltage System Interlock Circuit M High

Q: What does code U353C mean?

High Voltage System Interlock Circuit M High. U353C is a manufacturer-specific body code indicating that the high-voltage system interlock circuit, specifically the 'M' loop, has been detected at a voltage higher than the expected range. The vehicle's control module monitors this safety circuit and sets the code when the signal voltage exceeds the calibrated threshold, typically indicating a short to voltage or an open circuit in the interlock wiring.

U353C is a manufacturer-specific body code indicating that the high-voltage system interlock circuit, specifically the 'M' loop, has been detected at a voltage higher than the expected range. The vehicle's control module monitors this safety circuit and sets the code when the signal voltage exceeds the calibrated threshold, typically indicating a short to voltage or an open circuit in the interlock 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, especially in electric and hybrid models
Reduced power or limp-home mode due to high-voltage system shutdown
Audible chime or message indicating a high-voltage fault
Often no symptoms besides the warning light if the fault is intermittent

Common causes, most likely first

Damaged or chafed interlock wiring shorted to a higher voltage source
Faulty high-voltage interlock connector or terminal with poor pin tension
Failed high-voltage component (e.g., battery pack, inverter, or motor) internal interlock switch
Corrosion or moisture intrusion in the interlock circuit connector
Control module internal fault misreading the interlock voltage
Aftermarket accessories improperly wired into the high-voltage system

How to diagnose and fix it

Scan all modules for related codes and record freeze-frame data to understand when the fault occurs
Inspect the high-voltage interlock circuit wiring and connectors for damage, corrosion, or loose pins
Measure voltage on the interlock circuit at the control module and compare to manufacturer specifications
Disconnect and isolate high-voltage components one by one to see if the voltage reading normalizes
Check for technical service bulletins (TSBs) or software updates for the control module
Repair or replace damaged wiring, connectors, or the faulty high-voltage component as needed
Clear codes and perform a road test to verify the repair

Interlock Circuit Voltage Traps to Avoid

A short to voltage in the interlock circuit can be caused by a nearby 12-volt accessory wire rubbing against the interlock harness, which is often overlooked during visual inspection.
The 'M' circuit designation varies by manufacturer; some use it for a specific interlock loop, so always consult the factory wiring diagram for the exact vehicle.
High-voltage interlock circuits are designed to be low-voltage (typically 5V or 12V) for safety, so a 'high voltage' code refers to the signal, not the main battery pack voltage.
Intermittent faults often occur only when the vehicle is exposed to vibration or temperature extremes, making them hard to reproduce in the shop.
Replacing a high-voltage component without checking the interlock circuit voltage first can lead to repeat failures if the root cause is a wiring short.

Can I keep driving with U353C?

Do not continue driving with this code active, as the high-voltage system may be compromised and could shut down unexpectedly. Have the vehicle towed to a qualified service facility for diagnosis and repair.

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.