No Outside Air Temp. Display

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No Outside Air Temp. Display

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Chevrolet >> Chevy Cars >> Cobalt >> No Outside Air Temp. Display

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No Outside Air Temp. Display - 4/21/2008 11:28:37 AM

Chris777

Posts: 1
Joined: 4/21/2008
Status: offline

My outside air temp. display isn't displaying anything except ( _ _ _ ) Could it be unpluged or a bad senser and does anyone know where it is located at? Also a part # would be nice.
Thanks:)
Chris

Post #: 1

RE: No Outside Air Temp. Display - 4/21/2008 12:56:49 PM

shawnvw

Posts: 590
Joined: 1/18/2008
Status: offline

You didn't mention what year your cobalt was so i just chose a 2006. The sensor is 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 class 2 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 0-5 volts. 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 3 minutes)                                                                                   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

4.52-4.54                             94.63                                      -4                                            -20

4.22-4.25                             54.21                                      14                                            -10

3.81-3.85                             32.00                                      32                                              0

3.31-3.34                             19.61                                      50                                              10

2.76-2.79                             12.31                                      68                                             20

2.22-2.25                             7.959                                      86                                              30

1.73-1.75                             5.268                                     104                                             40

1.31-1.34                             3.563                                     122                                             50

0.99-1.01                             2.458                                     140                                             60

The Tech 2 will display sensor value as a voltage. This gives the approximate voltage expected at different ambient temperatures as well as what should be read with an ohmmeter connected to the sensor. Since this is raw data any heat from underhood that changes ambient temp around the sensor might skew the reading, so let the engine compartment cool.

< Message edited by shawnvw -- 4/21/2008 1:05:47 PM >

(in reply to Chris777)

Post #: 2