Outside air temperature problem
10-30-2007, 07:11 AM
#1
New Member
Thread Starter
Join Date: 10-23-2007
Location: Colubmia Gorge, Oregon
Posts: 10
Outside air temperature problem
The Outside air temperature indicator on my HHR is sluggish. When I start the car in the morning, it should stay on one temp. for about five minutes, and then begin to readout the correct OAT, right? Five minutes or less. Mine takes over half an hour to begin working, and sometimes goes all day without "waking up". Has anyone else had this problem? Just 800 miles, and this will be the second trip back to the dealer for corrections.
10-30-2007, 07:14 AM
#2
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Join Date: 10-19-2005
Location: Miami
Posts: 20,687
10-30-2007, 10:14 AM
#3
Senior Member
Join Date: 11-10-2006
Location: Montana
Posts: 163
This is a description of how the OAT sensor works. Its more complicated than one would think.
You will notice the very interesting information on how they changed the location of the sensor for 2008 models.
Outside Air Temperature
The outside air temperature is read by the body control module (BCM) and transmitted over serial data to the instrument panel cluster (IPC) for display in the driver information center (DIC). The BCM provides the logic for reading the outside air temperature sensor. The BCM sends the temperature to the IPC in Celsius. The IPC is responsible for displaying the temperature and converting to Fahrenheit.
The sensor operates within a temperature range of -40°C to +60°C (-40°F to +140°F). 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 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 than or equal to the old temperature value. Vehicle speed is in excess of 33 mph.
Displays outside actual temperature. Display updates every second.
If the current ambient air temperature value is warmer than the old temperature value. Vehicle speed is less than or drops below 18 mph.
Displays last temperature recorded during last ignition cycle. No update.
New ambient temperature exceeds the previous ignition cycle recorded ambient temperature, and vehicle speed exceeds 18 mph but is less than 33 mph.
Displays outside actual temperature. Display will be updated at a slow rate.
Vehicle speed is greater than or equal to 45 mph. (for at least 3 minutes)
Displays outside actual temperature Display updates at a quicker rate.
You will notice the very interesting information on how they changed the location of the sensor for 2008 models.
Outside Air Temperature
The outside air temperature is read by the body control module (BCM) and transmitted over serial data to the instrument panel cluster (IPC) for display in the driver information center (DIC). The BCM provides the logic for reading the outside air temperature sensor. The BCM sends the temperature to the IPC in Celsius. The IPC is responsible for displaying the temperature and converting to Fahrenheit.
The sensor operates within a temperature range of -40°C to +60°C (-40°F to +140°F). 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 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 than or equal to the old temperature value. Vehicle speed is in excess of 33 mph.
Displays outside actual temperature. Display updates every second.
If the current ambient air temperature value is warmer than the old temperature value. Vehicle speed is less than or drops below 18 mph.
Displays last temperature recorded during last ignition cycle. No update.
New ambient temperature exceeds the previous ignition cycle recorded ambient temperature, and vehicle speed exceeds 18 mph but is less than 33 mph.
Displays outside actual temperature. Display will be updated at a slow rate.
Vehicle speed is greater than or equal to 45 mph. (for at least 3 minutes)
Displays outside actual temperature Display updates at a quicker rate.
10-30-2007, 05:30 PM
#5
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Join Date: 11-10-2006
Location: Montana
Posts: 163
10-31-2007, 09:01 AM
#8
Senior Member
Join Date: 11-10-2006
Location: Montana
Posts: 163
01-01-2008, 06:37 PM
#9
New Member
Join Date: 10-01-2007
Location: Amarillo, TX
Posts: 10
My OAT on my 2007 seemed to be working OK. Just as GuitHHR described above. But after a firmware update just recently, there is no telling when or if the OAT will update. I left on a 360 mile trip - OAT - 34 degF. Two hours later radio station near my travelling location - 61 degF, which was pretty close to what it felt like when we stopped. DIC OAT 34 degF. On the road again and finally - 1 hour later DIC indicates OAT 65 degF. I drive Interstate to work, speed exceeds 45 mph for 5 minutes min, no chang in temp. Other times I drive less than a mile and temp starts to update. I don't know if the firmware update to BCM changed any parameters or if the connector has an issue. I'll have dealer check at next service need. I didn't know if OAT was used anywhere else for performance monitoring or just an indication for laughs and giggles.
Speaking of aftermarket fog/driving lights, what works best - use BCM wiring and logic or hardwire switch and bypass BCM. Sorry if off topic but I noticed someone found OAT sensor when installing aux lights. Thanks.
Speaking of aftermarket fog/driving lights, what works best - use BCM wiring and logic or hardwire switch and bypass BCM. Sorry if off topic but I noticed someone found OAT sensor when installing aux lights. Thanks.
01-01-2008, 07:48 PM
#10
Senior Member
Join Date: 09-02-2007
Location: Greencastle, PA
Posts: 152
The temp readout on my 08 seems to be pretty responsive. It will usually even change when I leave work and drive directly up a 2000ft. mountain from approx. 960 ft. (about 5 min. later) and most times I will see a change immediately. I usually compare it to a couple of bank thermometers on the way home and it is usuall within a degree or two of those.
TomR
TomR