P0128

What it means

Your car's engine isn't warming up to its normal operating temperature quickly enough, or it's running too cool, usually because the thermostat is stuck open.

Is it safe to drive?

While not usually an immediate breakdown risk, driving with a P0128 can lead to reduced fuel economy, increased emissions, and potentially premature engine wear due to the engine running outside its optimal temperature range. It's best to address it soon.

Most likely causes

• Faulty Thermostat (stuck open)

  high

  This is the most common cause; a thermostat stuck in the open position allows coolant to constantly flow through the radiator, preventing the engine from reaching optimal temperature.

• Faulty Engine Coolant Temperature (ECT) Sensor

  medium

  A malfunctioning ECT sensor can send incorrect temperature readings to the PCM, making it think the engine is too cold even if it's at normal operating temperature.

• Low Engine Coolant Level

  low

  Insufficient coolant in the system can lead to inaccurate temperature readings and inefficient heat transfer, preventing the engine from reaching or maintaining proper temperature.

• Cooling Fan Running Continuously

  low

  A faulty cooling fan relay or sensor can cause the fan to run constantly, over-cooling the engine and preventing it from reaching optimal temperature.

Related help

• Full P0128 diagnosis, causes & costs
• How to read check engine light codes
• Is it safe to drive with the light on?