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P0128

Overview

Code

P0128

Code Type

P

Code Class

P0

System

Engine

Severity Level

Low

Emissions Related

true

Drivability Impact

Minor

Diagnostic Protocol

OBD2

Freeze Frame Useful

true

Code Definition

Diagnostic trouble code P0128 indicates that the engine coolant temperature is below the thermostat regulating temperature for too long during operation

Symptoms

Check Engine Light illuminated; Poor fuel economy; Heater not producing warm air

Overview applies to this diagnostic code.

Affected Systems

On This Page

  • Code Definition

  • Symptoms

  • Affected Systems

  • Possible Causes

  • Diagnostic Steps

  • Drive Safety Notes​

More Resources

Engine cooling and emissions systems rely on proper thermostat operation

Possible Causes

Thermostat stuck open; Low coolant level; Faulty ECT sensor

Diagnostic Steps

1 Confirm the fault code; 2 Monitor coolant temperature during warm-up; 3 Inspect thermostat operation; 4 Check coolant level and condition; 5 Replace the thermostat if necessary

Drive Safety Notes

Driving is generally safe, but prolonged operation may increase emissions and reduce efficiency

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