Loose, damaged or corroded interlock terminals in a high voltage connector (battery, inverter, charger, compressor or heater); Interlock wiring chafed or shorted to a voltage supply; Service disconnect or HV cover not fully seated, or disturbed after recent work; Water ingress or contamination in an HV connector or component interlock circuit; Fault inside the module that drives or monitors the interlock loop; Internal interlock fault in an HV component such as the inverter, battery pack or charger.

U3548

High Voltage System Interlock Circuit P High.

Generic
Network
Generic code
High severity

How this code is built

U: SystemNetwork
3: Defined bySAE, the same on every car
5: AreaNetwork area 5
48: FaultThe specific fault in that area

What it means

U3548 means a control module monitoring the high voltage system interlock loop (HVIL) has found the 'P' circuit reading higher than expected. The interlock is a low-voltage safety loop that runs through high voltage connectors, covers and the service disconnect to confirm the system is sealed. A high reading usually points to a short to voltage or a fault in the loop. How the loop is split into circuits and what 'P' refers to varies by model, so check the manufacturer data for the vehicle.

Symptoms

High voltage system or hybrid/EV warning light on the dash
Car will not go into ready mode or will not start
Reduced power or limp mode while driving
High voltage system shuts down unexpectedly
Charging will not start or stops early
Other communication or HV-related fault codes stored alongside

Possible causes

Loose, damaged or corroded interlock terminals in a high voltage connector (battery, inverter, charger, compressor or heater)likely
Interlock wiring chafed or shorted to a voltage supplylikely
Service disconnect or HV cover not fully seated, or disturbed after recent workpossible
Water ingress or contamination in an HV connector or component interlock circuitpossible
Fault inside the module that drives or monitors the interlock looprare
Internal interlock fault in an HV component such as the inverter, battery pack or chargerrare

How to diagnose

Read all stored codes and freeze frame data, noting whether the fault is current or intermittent and what other HV or network codes are present
Check for any recent HV or body work and confirm that the service disconnect and all HV covers are correctly fitted
Make sure the high voltage system is isolated and proven dead by a suitably trained person before touching any orange HV connector or cable
Visually inspect interlock connectors, terminals and wiring for damage, bent pins, corrosion, moisture or chafing, following the manufacturer's procedure
Look up the loop layout for the model and identify the circuit and components that make up the 'P' side of the interlock
With the HV system isolated, measure the interlock circuit for short to voltage, continuity and resistance against the manufacturer's specification
Check the interlock supply and signal at the monitoring module, and carry out a wiggle test while watching live data for the status changing
Clear the code after repair and retest to confirm it does not return

How to fix

Reseat and secure the service disconnect, HV connectors and covers correctly
Repair or replace damaged interlock wiring and clean or replace corroded or damaged terminals
Dry out and rectify any water ingress, and replace any connector that is damaged or contaminated
Replace the HV component or harness found to have an internal interlock fault, following the manufacturer's procedure
Repair or replace the module that monitors the loop only after wiring and connectors have been proven good, and update software if the manufacturer lists it as a known fix

Can I keep driving?

High severity

Do not keep driving if the HV warning is lit or the car is losing power, as the system may shut down without warning. The work involves high voltage, so have it inspected by a technician trained in HV systems.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.