Faulty interlock switch or sensor integrated into a high-voltage connector; Damaged or corroded wiring in the interlock circuit M, including open or short to ground; Loose or improperly seated high-voltage connector, causing the interlock loop to open; Water intrusion or contamination in a high-voltage connector or component; Internal failure in a high-voltage component (e.g., battery pack, inverter, motor) affecting the interlock circuit; Poor electrical connection at the control module or a faulty control module

DTC codes / U35xx · Network communication / U353B

U353BHigh Voltage System Interlock Circuit M Low

Q: What does code U353B mean?

High Voltage System Interlock Circuit M Low. U353B indicates that the high-voltage system interlock circuit M has been detected as having a low voltage condition, which the vehicle's control module interprets as a potential safety hazard. The interlock is a low-voltage loop that runs through high-voltage connectors and components; when its voltage drops below the expected threshold, the module sets this code to prevent operation of the high-voltage system.

U353B indicates that the high-voltage system interlock circuit M has been detected as having a low voltage condition, which the vehicle's control module interprets as a potential safety hazard. The interlock is a low-voltage loop that runs through high-voltage connectors and components; when its voltage drops below the expected threshold, the module sets this code to prevent operation of the high-voltage system.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork communication

Symptoms you may notice

High-voltage system disabled, preventing the vehicle from starting or driving
Illumination of the high-voltage warning light or service vehicle soon message
Reduced power or limp mode if the vehicle is still operable
Audible alert or chime indicating a high-voltage fault
Often no symptoms besides the warning light, especially if the interlock fault is intermittent

Common causes, most likely first

Faulty interlock switch or sensor integrated into a high-voltage connector
Damaged or corroded wiring in the interlock circuit M, including open or short to ground
Loose or improperly seated high-voltage connector, causing the interlock loop to open
Water intrusion or contamination in a high-voltage connector or component
Internal failure in a high-voltage component (e.g., battery pack, inverter, motor) affecting the interlock circuit
Poor electrical connection at the control module or a faulty control module

How to diagnose and fix it

Perform a visual inspection of all high-voltage connectors and wiring for damage, corrosion, or loose connections
Use a scan tool to check for related codes and freeze-frame data to identify the affected circuit
Measure resistance and voltage on the interlock circuit M to check for opens, shorts, or excessive resistance
Disconnect and reseat each high-voltage connector, checking for proper engagement and clean terminals
Test the interlock switch or sensor with a multimeter and replace if faulty
Inspect for water intrusion or debris in connectors and clean or dry as necessary
If the fault persists, follow the manufacturer's diagnostic flow chart to test the control module and high-voltage components

Interlock Circuit M Low-Voltage Pitfalls

A low-voltage condition on the interlock circuit often results from a partially disconnected connector rather than a failed component, so always check connector engagement first.
The interlock circuit is a safety loop; a fault in any high-voltage connector can set this code, not just the one labeled 'M'.
Some vehicles may set this code intermittently due to vibration or temperature changes, making it important to wiggle-test connectors while monitoring live data.
Do not assume the high-voltage battery is faulty; the interlock circuit is separate and a simple wiring repair often resolves the issue.
After repairs, the code may require a specific reset procedure or clearing of safety flags before the high-voltage system will re-enable.

Can I keep driving with U353B?

Do not drive the vehicle with this code active, as the high-voltage system may be disabled or in a unsafe state. Have the vehicle inspected by a qualified high-voltage technician before attempting to drive.

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.