Kia Niro 4 Plus (2020-2022) Isolation Fault, Inverter Coolant Ingress and HV Battery Contactor Repair
Low isolation vehicle side
High-voltage isolation fault
Coolant ingress inside the inverter
Vehicle unable to enter ready mode
The following fault code(s) may be present
No specific fault codes were provided
Do you have a Kia Niro with an isolation fault, inverter failure, or HV battery contactor issue?
Don't ignore it. Book an initial inspection today and get expert help.
Parts Repaired/Replaced
- Inverter replaced with an OEM recycled unit
- HV battery contactor pack removed and repaired/replaced
- Blown HV fuse identified and replacement parts sourced and fitted
Affected Vehicles
Kia Niro 4 Plus
- Kia Nero 4 Plus 2020
- Kia Nero 4 Plus 2021
- Kia Nero 4 Plus 2022
Common Failure Symptoms
- Vehicle fails to enter ready mode
- Low insulation resistance / isolation fault on the HV system
- Inverter contamination or coolant ingress
- HV battery contactor relays welded shut or HV fuse failure
Kia Niro Diagnostic Report
Initially, high-voltage checks found low isolation on the vehicle side. Our EV technician disconnected HV equipment one component at a time to isolate the fault. After removing the HV junction box, the fault was narrowed down to the inverter or motor.
Subsequently, the inverter internals were tested and coolant ingress was found inside the inverter. The motor passed both insulation resistance and winding resistance tests, confirming it was within specification.
Kia Niro Repairs
The inverter was found to be beyond repair due to coolant ingress, so an OEM recycled unit was required. The inverter control board had contamination which needed attention to ensure it was operational and within specification.
Further investigation identified an additional HV battery issue. The HV battery was removed and opened. The contactor pack was removed and welded relays were found. The service plug and fuse housing were also removed, where a blown fuse was identified.
- Disconnected HV equipment and tests carried out to isolate the low-isolation fault
- Removed the HV junction box and traced the fault to the inverter or motor circuit
- Tested inverter internals and confirmed coolant ingress - OEM replacement fitted
- Tested the motor insulation and winding resistance, both of which passed
- Removed the HV battery lid and contactor pack - identified welded contactor relays and a blown HV fuse
- Carried out vehicle resets, and post repair procedures to ensure within specified parameters
Resolution
Following the repair, the HV battery was refitted and vehicle resets were completed. Post repair procedures carried out. The vehicle entered ready mode and drove successfully. Final checks confirmed the vehicle was complete and ready to go.
Following the repair:
- Vehicle entered ready mode
- Vehicle drove successfully
- Final quality checks were completed
- Vehicle was given extended road test prior to release
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