U353A

Code

Generic U — Network/User

High Voltage System Interlock Circuit M Performance

Brand: Generic

Type: U — Network/User

Views: UK: 37 EN: 28 RU: 20

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or shorted wiring in the HV interlock circuit (connector damage, chafing, pin corrosion)
Faulty interlock switch or sensor in connector/service plug/cover
High-resistance connection at an HV interlock connector (corrosion, bent pins, contamination)
Loose or unseated HV interlock connector or service plug
Water intrusion or corrosion at interlock connector
Failed control module input or internal module fault

Symptoms

HV system disabled or disabled for charging/drive (vehicle may enter limp or reduced-power mode)
HV system warning lamp or master warning illuminated
Inability to charge or start electric propulsion
Diagnostic trouble code U353A stored in HV control or body control module
Intermittent loss of HV functionality (fault may clear and return)
Possible reduced functionality of other HV-related systems

What to check

Verify the code is current and note freeze-frame/DTM data with a scan tool; attempt to clear code and see if it returns
Check for related DTCs on HV battery, inverter, and body/control modules
Visually inspect all HV interlock connectors, service plug, covers and their harnesses for damage, corrosion or water intrusion
Confirm service disconnect/service plug is fully seated and locked per manufacturer procedure
Check fuses and relays related to interlock sensor supply and reference voltages
Measure interlock circuit voltage and continuity at module connector and at the interlock switch with the system in the correct state (see signal parameters)

Signal parameters

Interlock signal uses vehicle reference (commonly 5 V) and switches to ground when closed — expected voltages: ≈0 V (closed) or ≈reference voltage (open).
Typical closed-state resistance: low (< 5 Ω) when measured across switch contacts (values vary by design).
Typical open-state resistance: very high (> 10 kΩ) or open circuit.
No destructive current expected through the interlock switch — only logic-level sensing current.
Signal should be stable (no rapid fluctuation) with connector fully engaged; intermittent pulses indicate poor contact or wiring faults.

Diagnostic algorithm

SAFETY FIRST: Follow all manufacturer HV safety procedures. Disable HV system, remove service disconnect, and wear required PPE before handling high-voltage components or connectors.
Use a scan tool to confirm U353A is present, capture any freeze frame data, and check for related codes on HV and body modules.
Visually inspect the interlock switch, service plug area, and wiring harness for damage, corrosion, moisture, or loose connectors. Repair or replace obvious physical damage.
With HV system disabled and service disconnect removed, disconnect the interlock connector and inspect pins for corrosion, bending, or contamination. Clean or repair as needed.
Reconnect vehicle power per safe procedure to allow signal testing (only if allowed by vehicle procedures). Measure interlock signal voltage at the control module connector and at the interlock switch while changing the interlock state (engaged/disengaged). Compare to expected signal parameters.
Perform continuity and resistance checks with the circuit de-energized: verify low resistance when switch closed and high resistance when open. If readings are out of spec, replace or repair wiring/connector or switch.
Perform a wiggle test of the harness and connectors while monitoring the interlock signal for intermittent changes that would indicate a poor contact or intermittent short.
Inspect and test related fuses and power/reference supplies to the interlock circuit. Repair faulty supplies if found.
If wiring and connector are good, substitute or bench-test the interlock switch assembly if possible, or replace the suspect interlock component.
If all hardware checks good, verify CAN or module communications and update or reflash modules per manufacturer TSBs if firmware issues are suspected.
After repairs, clear stored codes, cycle the vehicle to re-enable HV systems following safety procedures, and perform a road or function test to confirm the fault does not return.

Likely causes

Loose, corroded or damaged interlock connector at a service plug or HV connector
High-resistance contact in the interlock switch (wear, contamination)
Intermittent open circuit in interlock wiring due to chafing or connector pin damage
Faulty interlock sensor/switch assembly