P0128 on Chrysler
Coolant Thermostat Below Regulating Temperature
P0128 on Chrysler vehicles indicates coolant thermostat below regulating temperature. Au7o has documented this code across 7 Chrysler models — most commonly on 300, Cirrus, Pacifica. 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 Chrysler range from $100 to $8,000, 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 Chrysler by Model
Chrysler 300(1 issue)
- Water Pump Failure and Cooling Leaks2011-2023
Water pumps fail prematurely due to bearing and seal wear. Air pockets frequently form in cooling system after repairs. The 300 is difficult to properly bleed air from cooling system.
Chrysler Cirrus(1 issue)
- 2.5L V6 Head Gasket Failure1995-2000
The Cirrus equipped with the Mitsubishi-sourced 2.5L V6 is prone to head gasket failure, often caused by overheating episodes. The engine's aluminum heads warp easily when overheated, making a simple gasket replacement insufficient without machining the heads.
Chrysler Pacifica(1 issue)
- 3.6L Pentastar Engine Stalling and Head Gasket Failure2017-2024
The 3.6L Pentastar V6 in Pacifica models suffers from engine stalling due to loose ground connections (recall NHTSA 19V348), crankshaft position sensor sync issues, and premature head gasket failures typically around 75,000-85,000 miles. Cooling system failures can lead to coolant entering the combustion chamber, requiring complete engine replacement.
Chrysler Prowler(1 issue)
- 3.5L V6 Coolant Crossover Tube Leak1999-2002
The Chrysler 3.5L V6 engine in the Prowler uses aluminum coolant crossover tubes that develop leaks at the O-ring seals and crimped connections. The crossover tubes run across the top of the engine between the cylinder heads and are exposed to high heat. The O-rings harden and shrink, allowing coolant to seep. The Prowler's unique front-end design with exposed engine makes the leak visible but also means the engine compartment lacks the heat shielding of a conventional car.
Chrysler PT Cruiser(3 issues)
- Chronic Overheating - Multiple Causes2001-2010
PT Cruisers are extremely prone to overheating from multiple causes: radiator fan relay failure, fan motor failure, thermostat sticking closed, radiator clogging, and water pump failure. The high-speed fan relay is the most frequent single failure point. Overheating leads to head gasket failure. This is one of the most universally reported problems across all model years.
- Head Gasket Failure (Especially Turbo Models)2001-2010
Head gasket failure is common, especially on turbo models. The aluminum cylinder head is susceptible to pitting from acidic coolant which compromises the gasket seal. Turbo models experience higher cylinder pressures that accelerate failure. Overheating from cooling system issues frequently triggers head gasket failure.
- Turbocharger Failure (GT/Turbo Models)2003-2010
The turbocharger on GT and turbo models fails from oil starvation, wastegate actuator failure, and bearing wear. Failures reported as early as 60,000-78,000 miles. Turbo failure is often followed by head gasket failure within months due to changes in combustion pressure dynamics.
Chrysler Sebring(1 issue)
- 3.5L V6 Head Gasket Failure and Overheating2001-2010
The 3.5L V6 engine has common issues including leaky head gaskets, coolant leaks, and overheating. The water pump uses a molded plastic impeller that erodes from rust and sediment in the coolant, reducing cooling efficiency. These engines run hot and are prone to oil sludging, especially if oil is not changed every 3,000 miles.
Chrysler Town & Country(1 issue)
- Cooling System Failures (3.3L/3.8L V6)2001-2010
The 3.3L and 3.8L V6 engines suffer from water pump failures, thermostat failures, and radiator fan relay failures. The water pump weep hole is a common leak point. Overheating can cause head gasket failure. The cooling fan relay is a frequent failure point causing overheating at idle.
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View P0128 across all makes →Frequently Asked Questions
What does P0128 mean on Chrysler?▼
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 Chrysler specifically, this code is documented across 7 models.
What causes P0128 on Chrysler vehicles?▼
Common causes on Chrysler: 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 Chrysler?▼
Repair costs on Chrysler range from $100 to $8,000, depending on the specific model and root cause.
Which Chrysler models have P0128 documented?▼
Au7o has documented P0128 on 7 Chrysler models: 300, Cirrus, Pacifica, Prowler, PT Cruiser, Sebring, Town & Country.