P0128 on Dodge
Coolant Thermostat Below Regulating Temperature
P0128 on Dodge vehicles indicates coolant thermostat below regulating temperature. Au7o has documented this code across 12 Dodge models — most commonly on Avenger, Caliber, Challenger. 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 Dodge range from $100 to $6,000, 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 Dodge by Model
Dodge Avenger(1 issue)
- Heater Core Failure - Dashboard Removal Required2008-2014
Heater core plugs with debris or develops leaks. Causes loss of heat, coolant smell in cabin, fogging windshield, and coolant loss. Dashboard must be removed for replacement, making it one of the most labor-intensive repairs (8-12 hours).
Dodge Caliber(1 issue)
- Engine Overheating - Multiple Causes2007-2012
Calibers are prone to overheating from radiator fan failure, thermostat sticking, water pump failure, and radiator clogging. Same cooling system shared with Jeep Compass/Patriot (PM/MK platform). Fan relay failure is the most common single cause.
Dodge Challenger(1 issue)
- Pentastar 3.6L Oil Filter Housing Leak2011-2023
The plastic oil filter housing warps and cracks from heat cycling, causing oil leaks from front of engine near oil filter. In severe cases coolant and oil can mix. Common across all Pentastar 3.6L vehicles (Challenger, Charger, 300, Jeep, Ram).
Dodge Grand Caravan(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 sticking, and radiator fan relay failures. Overheating can cause head gasket failure. Fan relay is the most common single failure point. Same cooling system as Chrysler Town & Country.
Dodge Hornet(1 issue)
- Electrical and Software Malfunctions2023-2025
First-year production teething issues on the Alfa Romeo Tonale platform. Wiring harness failures, battery control module failures, touchscreen freezes, front collision warning malfunctions, start/stop issues, and wireless charging overheating.
Dodge Journey(2 issues)
- Engine Overheating - Thermostat Housing Debris2009-2016
Debris accumulates in cylinder head coolant port at primary thermostat housing, blocking coolant flow and causing overheating. Typically occurs around 78,000 miles. Can cause head gasket failure or engine damage if not addressed.
- Head Gasket Failure2013-2015
2014 models with 2.4L engine notorious for head gasket failures around 100,000 miles. Fails due to overheating issues and possible manufacturing defects in gasket material or cylinder head warping. Plastic thermostat housing contributes to overheating.
Dodge Neon(2 issues)
- Timing Belt Failure - ALL Engines Are Interference2000-2005
ALL Neon engines (SOHC and DOHC) are interference engines where timing belt failure causes catastrophic valve-to-piston contact and engine destruction. Belt replacement required at 100,000 miles. Water pump is driven by timing belt and must be replaced simultaneously.
- Head Gasket Failure and Coolant Loss1995-2005
The 2.0L engines are prone to head gasket failure, causing external coolant leaks, white exhaust smoke, and eventual overheating. The SOHC engines are more commonly affected than the DOHC variant.
Dodge Nitro(1 issue)
- Thermostat Housing Leak and Overheating2007-2011
The plastic thermostat housing cracks and leaks coolant, especially on the 3.7L V6. The housing is made of nylon composite that becomes brittle with heat exposure over time.
Dodge Shadow(1 issue)
- 2.2L/2.5L Head Gasket Failure1990-1994
The 2.2L and 2.5L Chrysler K-car engines in the Shadow are prone to head gasket failure, especially after overheating episodes. The cast iron block and aluminum head expand at different rates, causing the head gasket to lose its seal over time. The 2.5L is more prone than the 2.2L due to higher combustion pressures. Coolant leaking externally at the rear of the head or internally causing white exhaust smoke are the primary symptoms. The turbo 2.2L variants are particularly susceptible due to higher cylinder pressures. These engines use a composite head gasket that has been superseded by improved designs.
Dodge Spirit(1 issue)
- 2.2L/2.5L Head Gasket Failure1990-1995
The Dodge Spirit shares the same 2.2L and 2.5L K-car engines as the Shadow and suffers from the identical head gasket failure pattern. The bimetallic construction (cast iron block, aluminum head) creates differential thermal expansion that breaks down the composite head gasket seal. The 2.5L is more commonly affected due to higher combustion pressures. The Spirit R/T model with the 2.2L turbo is particularly susceptible due to boost pressure stressing the gasket. Overheating from any cause (stuck thermostat, failed fan, low coolant) often triggers immediate head gasket failure on these engines.
Dodge Stratus(1 issue)
- 2.4L DOHC Head Gasket Failure1995-2006
The 2.4L DOHC 4-cylinder engine (used across both Stratus generations) is prone to head gasket failure, particularly when overheating occurs. The aluminum cylinder head warps more easily than cast iron, and once warped, the head gasket cannot maintain a proper seal. Coolant mixing with oil or exhaust gases entering the cooling system are the primary failure modes. While more reliable than the 2.7L V6, the 2.4L still requires careful cooling system maintenance. The factory composite head gasket has been superseded by improved MLS (multi-layer steel) designs.
Dodge Viper(1 issue)
- Gen 1 V10 Head Gasket Failure1992-1995
Composite head gasket design inadequate for V10 heat output. Gen 2 (1996+) upgraded to MLS gasket which resolved the issue. Gen 1 owners should upgrade to MLS design during any head work.
Looking for P0128 on a different make?
View P0128 across all makes →Frequently Asked Questions
What does P0128 mean on Dodge?▼
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 Dodge specifically, this code is documented across 12 models.
What causes P0128 on Dodge vehicles?▼
Common causes on Dodge: 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 Dodge?▼
Repair costs on Dodge range from $100 to $6,000, depending on the specific model and root cause.
Which Dodge models have P0128 documented?▼
Au7o has documented P0128 on 12 Dodge models: Avenger, Caliber, Challenger, Grand Caravan, Hornet, Journey, Neon, Nitro, Shadow, Spirit, Stratus, Viper.