Closed Loop Temp Not Reached

Name of Code:
Closed Loop Temp Not Reached

When Monitored:
After engine is started, for ten minutes.

Set Condition:
The engine temperature does not go above 18°F by 10 minutes after the engine is started. Two trips are required to set this code.

Theory of Operation:
The engine coolant temperature sensor is a negative temperature coefficient (NTC) thermistor-type sensor (resistance varies inversely with temperature). This means at cold temperatures its resistance is high so the voltage signal will be high. As coolant temperature increases, resistance decreases and the voltage will be low. This allows the sensor to provide an analog voltage signal (0 to 5-volt) to the PCM.

Possible Causes:
- Thermostat failure
- ECT failure
- Extremely cold ambient temperature
- PCM failure
- Connector wires
- Connector terminals