P0128 on Kia
Coolant Thermostat Below Regulating Temperature
P0128 on Kia vehicles indicates coolant thermostat below regulating temperature. Au7o has documented this code across 4 Kia models — most commonly on Seltos, Sorento, Sportage. This code means the engine isn't reaching its proper operating temperature within the expected time, so the coolant stays below the thermostat's regulating temperature. The computer estimates how warm the coolant should be (based on run time, airflow, and intake air temperature) and compares it to the actual reading. When the engine warms too slowly or never gets hot enough, P0128 sets. The most common cause is a thermostat stuck open, which can cause reduced heater output, poorer fuel economy, and higher emissions.
Common Causes of P0128
- •Thermostat stuck open or opening too early
- •Faulty engine coolant temperature sensor
- •Low coolant level
- •Cooling fan running constantly (overcooling)
- •Wrong-temperature-rating thermostat installed
- •Corroded or loose coolant temperature sensor connector
- •Air pockets in the cooling system
- •Faulty PCM/ECM (rare)
P0128 on Kia by Model
Kia Seltos(1 issue)
- Idle Stop & Go Oil Pump Overheating2023-2024
The ISG (Idle Stop & Go) oil pump electronic controller in 2023-2024 Seltos vehicles may contain damaged electrical components that cause the pump to overheat, increasing fire risk. NHTSA Recall 23V-578 covers affected Seltos and Sportage vehicles. Kia replaces the ISG oil pump assembly.
Kia Sorento(1 issue)
- HECU Electrical Short and Engine Compartment Fire Risk2011-2014
The Hydraulic Electronic Control Unit (HECU) in the ABS module can develop an internal electrical short circuit, causing the unit to overheat and potentially ignite an engine compartment fire even while the vehicle is parked. NHTSA Recall 19V-085 covers over 70,000 Sorentos. Kia dealers will replace the HECU fuse and inspect for leaks, replacing the entire HECU assembly if signs of damage are found.
Kia Sportage(2 issues)
- HECU Electrical Short / Fire Risk2012-2016
The Hydraulic Electronic Control Unit (HECU) in the ABS brake module can develop an internal electrical short, causing overheating and potential engine compartment fire. This can occur while driving or while the vehicle is parked. NHTSA Recall 18V-743 and subsequent recalls cover affected Sportages. Kia installs a lower-amperage fuse and inspects the HECU for damage.
- Idle Stop & Go Oil Pump Overheating2023-2024
Certain 2023-2024 Sportage vehicles have an electronic controller in the Idle Stop & Go (ISG) oil pump assembly that may contain damaged electrical components. The damaged components can cause the oil pump to overheat, increasing the risk of a vehicle fire. NHTSA Recall 23V-578 covers affected vehicles. Kia dealers replace the ISG oil pump assembly.
Kia Telluride(1 issue)
- Front Power Seat Motor Overheating / Fire Risk2020-2024
The front power seat motor can overheat if the power seat slide knob becomes stuck, causing the motor to run continuously. This can result in a fire even while the vehicle is parked. NHTSA recall covers approximately 462,869 Tellurides from 2020-2024 model years. Kia dealers install a bracket for the power seat switch back covers and replace the seat slide knobs.
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View P0128 across all makes →Frequently Asked Questions
What does P0128 mean on Kia?▼
P0128 stands for "Coolant Thermostat Below Regulating Temperature." This code means the engine isn't reaching its proper operating temperature within the expected time, so the coolant stays below the thermostat's regulating temperature. The computer estimates how warm the coolant should be (based on run time, airflow, and intake air temperature) and compares it to the actual reading. When the engine warms too slowly or never gets hot enough, P0128 sets. The most common cause is a thermostat stuck open, which can cause reduced heater output, poorer fuel economy, and higher emissions. On Kia specifically, this code is documented across 4 models.
What causes P0128 on Kia vehicles?▼
Common causes on Kia: Thermostat stuck open or opening too early, Faulty engine coolant temperature sensor, Low coolant level, Cooling fan running constantly (overcooling), Wrong-temperature-rating thermostat installed. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0128 on a Kia?▼
Repair costs vary widely depending on the root cause and specific Kia model.
Which Kia models have P0128 documented?▼
Au7o has documented P0128 on 4 Kia models: Seltos, Sorento, Sportage, Telluride.