P0128 on Infiniti
Coolant Thermostat Below Regulating Temperature
P0128 on Infiniti vehicles indicates coolant thermostat below regulating temperature. Au7o has documented this code across 1 Infiniti model — most commonly on FX50. 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. Typical repair costs on Infiniti range from $300 to $1,400, depending on the specific model and root cause.
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 Infiniti by Model
Infiniti FX50(1 issue)
- Radiator / Cooling Fan Related Overheating2009-2013
As these vehicles age, cooling system issues such as radiator seepage, fan control problems, or thermostat degradation can lead to elevated engine temperatures. The VK50VE V8 runs hot under load, so any reduction in cooling efficiency can quickly cause overheating, especially in traffic or hot climates.
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View P0128 across all makes →Frequently Asked Questions
What does P0128 mean on Infiniti?▼
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 Infiniti specifically, this code is documented across 1 model.
What causes P0128 on Infiniti vehicles?▼
Common causes on Infiniti: 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 Infiniti?▼
Repair costs on Infiniti range from $300 to $1,400, depending on the specific model and root cause.
Which Infiniti models have P0128 documented?▼
Au7o has documented P0128 on 1 Infiniti model: FX50.