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Home/DTC Codes/Lincoln/MKX/2018-2018 3.7L V6/P0128
P0128

Coolant Thermostat Below Regulating Temperature

2018-2018 Lincoln MKX 3.7L V6

Low SeverityPowertrainGeneric (SAE)

The 2018 Lincoln MKX is equipped with a 3.7L V6 engine. Below you'll find detailed p0128 diagnostic code information including labor time estimates, cost ranges, and technician notes specific to this engine configuration.

Description

The engine coolant has not reached the expected temperature within a specified time after startup.

Symptoms

  • Check Engine Light
  • Poor fuel economy
  • Heater not getting hot
  • Engine running cool

Common Causes

  • Stuck-open thermostat
  • Missing thermostat
  • Faulty ECT sensor
  • Cooling fan stuck on

Diagnostic Steps

  1. Monitor ECT warmup curve
  2. Check thermostat
  3. Verify fan operation
  4. Test ECT sensor

Repair Notes

Replace thermostat.

Related Codes

P0115Engine Coolant Temperature (ECT) Sensor 1 CircuitP0116ECT Sensor 1 Circuit Range/PerformanceP0125Insufficient Coolant Temperature for Closed Loop Fuel Control

Other Powertrain Codes

P0128 on Other Vehicles

Lincoln Aviator

2003-2003 4.6L V8 DOHC

Lincoln Aviator

2004-2004 4.6L V8 DOHC

Lincoln Aviator

2005-2005 4.6L V8 DOHC

Lincoln Aviator

2020-2020 3.0L Twin-Turbo V6

Lincoln Aviator

2020-2020 3.0L V6 Twin Turbo

Lincoln Aviator

2020-2020 3.0L V6 Twin Turbo Hybrid

Lincoln Aviator

2021-2021 3.0L Twin-Turbo V6

Lincoln Aviator

2021-2021 3.0L V6 Twin Turbo

Common Questions

What does code P0128 mean on a 2018-2018 Lincoln MKX?

P0128 stands for "Coolant Thermostat Below Regulating Temperature". The engine coolant has not reached the expected temperature within a specified time after startup.

What are the symptoms of P0128 on a Lincoln MKX?

Common symptoms of P0128 include: Check Engine Light, Poor fuel economy, Heater not getting hot, Engine running cool.

What causes P0128 on a 2018-2018 Lincoln MKX?

Common causes of P0128 include: Stuck-open thermostat, Missing thermostat, Faulty ECT sensor, Cooling fan stuck on.

Last updated: March 2026

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