04-21-2008, 02:56 PM
Join Date: Jan 2008
RE: No Outside Air Temp. Display
You didn't mention what year your cobalt was so i just chose a 2006. The sensoris mounted to the right side of the left headlamp behind the grille.
The should be 2 wires going to the sensor, one is 5v, and the other varies in voltage depending on temperature.
Here's a description on how it works, and a Table on what resistances you should be getting(roughly) at different temperatures.
Ambient Air Temperature Sensor
The ambient air temperature sensor is a 2-wire negative temperature co-efficient thermistor.
A 5-volt reference and signal circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases.
The sensor operates within a temperature range of -40°C to +60°C (-40°F to +140°F). The HVAC control module receives a class2 message from the instrument panel cluster (IPC). The ambient air temperature sensor is mounted in the forward engine area, behind the left front headlamp. This causes an air flow issue due to the sensor's location and can effect the ambient air update display parameter in the DIC of the vehicle. For model year 2008 the ambient air temperature sensor will have a new location closer to the grill airflow. In the present position, it is exposed to limited airflow from the grill before it reaches the radiator. The sensor signal varies between 0-5volts. The HVAC control module converts the signal to a working temperature range.
The ambient air temperature sensor algorithm uses 3 pieces of information, outside air temperature data, vehicle speed, and time the engine was turned off.
The ambient air temperature is updated and displayed by the DIC under the following conditions:
Conditions DIC Display
If the current ambient air temperature value is cooler Displays outside actual temperature.
than or equal to the old temperature value. Display updates every second.
Vehicle speed is in excess of 33 mph.
If the current ambient air temperature value is warmer Displays last temperature recorded
than the old temperature value. Vehicle speed is less during last ignition cycle. No update.
than or drops below 18 mph.
New ambient temperature exceeds the previous ignition Displays outside actual temperature.
cycle recorded ambient temperature, and vehicle speed Display will be updated at a slow rate.
exceeds 18 mph but is less than 33 mph.
Vehicle speed is greater than or equal to 45 mph. Displays outside actual temperature
(for at least 3minutes) Display updates at a quicker rate.
Sensor Resistance Table (Volts to Temp to Resistance)
Voltage Tech 2 (V) R Nominal (k ohms) Outside Air Temp (°F) Outside Air Temp (°C)
4.72-4.74 171.6 -22 -30
If you have a question, ask it in the forums. I will no longer be answering questions sent to my email.