Car has no heat

[LEWETHETIGER73]

A 2006 Grand Prix. The fan still works but just cold air. Thinking it might be the T-stat but not sure. Anything else to look at on these newer cars?

[Korndogg]

either the t-stat or the heater core is plugged. You can try to reverse flush the system.

[Reverend Cooper]

well for one what does the temp gauge do after its been running for 10 min.

[LEWETHETIGER73]

temp gauge is normal. How do you reverse flush? Drive full speed in reverse :D

[Korndogg]

they have kits that you can buy that hook up to the heater hoses.

[88Nightmare]

is the coolant level normal for starters? I'd flush it and do a t-stat. both are cheap. any moisture on your front passenger floor? Also, do you have the automatic climate control? Some GM vehicles have issues with the electronic temperature blend solenoids. My 2006 silverado had an issue with that. When I'd adjust for heat, it just kept giving me cool air. Everything about the coolant system was fine, as was the hvac controls... just ended up being a temp control solenoid in the dash.

[LEWETHETIGER73]

Is there a way to test the solenoid?

[88Nightmare]

Does your car have the "automatic" dual zone climate control or the "manual" dual zone climate control? I am just going to assume you have the automatic, and your GP is either a GTP or GXP.

Try this:

AIR TEMPERATURE DESCRIPTION AND OPERATION

The air temperature controls are divided into three primary areas:

Automatic operation
The heating and air conditioning system
The air conditioning (A/C) cycle

HVAC CONTROL COMPONENTS

HVAC Control Module
http://www.alldatapro.com/alldata/PRO~V243198088~C42066~R0~OB0~P3R0H~N/0/115013665/117376357/117376400/117376406/34853741/34865608/34866115/129116488/129116498/119131069/119131070

The HVAC control module is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle power mode master, provides a device on signal. The control module supports the features.

Personalization
The HVAC control module will receive information that defines the current driver of the vehicle from the driver door module (DDM) through class 2 communication. The HVAC system will memorize the following system configurations for up to three unique drivers:

Driver set temperature
Passenger set temperature
Mode
Blower motor speed (auto, speed 1, 2, 3, 4, 5, 6)
Air conditioning (A/C) compressor request, auto ON or A/C OFF

This information shall be stored inside the HVAC control module memory. When a different driver identification button is selected the HVAC control module will recall the appropriate driver settings. When the HVAC control module is first turned on, the last stored settings for the current driver will be activated except for the rear defrost and heated seat settings.

Air Temperature Actuators
The air temperature actuator is a 2-wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to co-ordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 12 volts . In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.

The HVAC control module determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across two commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position.


Air Temperature Sensors
The air temperature sensors are 2-wire negative temperature co-efficient thermistors. The vehicle uses the following air temperature sensors:

Outside
Inside
Upper right
Upper left
Lower right
Lower left

http://www.alldatapro.com/alldata/PRO~V243198088~C42066~R0~OB0~P3R0H~N/0/115013665/117376357/117376400/117376406/34853741/34865608/34866115/129116488/129116498/119131069/119131071
The upper and lower duct sensors are divided into left and right zone operation. The left side upper and lower duct sensors will only effect the operation of the left air temperature actuator and the right side upper and lower duct sensors will only effect the operation of the right air temperature actuator. The duct sensors are used to measure the temperature of the air exiting the ducts. The sensors operate within a temperature range between -6.5-57.5°C (20.3-135.5°F) . When temperature increases the sensor signal decreases. The HVAC control module converts the 0-5 volt sensor signal to a range between 0-255 counts. If the HVAC control module detects that one of the duct temperatures must change, the HVAC control module will adjust the appropriate air temperature actuator. The given list shows the duct sensors that are monitored by the HVAC control module in each mode position:

If the HVAC control module detects a malfunctioning sensor, the HVAC system will only malfunction when the sensor is monitored.

The inside temperature sensor operates within a temperature range between -6.5-57.5°C (20.3-135.5°F) . If the sensor is shorted to ground, an open, or shorted to voltage, the HVAC system will use a default value.

The outside temperature sensor operates within a temperature range between -30-51°C (-22-123.8°F) . The radio displays the OAT value that it receives from the HVAC control module through a class 2 message. If the HVAC control module has determined that the outside temperature sensor has failed, the radio shall display, 75, in place of the outside air temperature. If the sensor is shorted to ground, an open, or shorted voltage, the HVAC control module will use a default value.

http://www.alldatapro.com/alldata/PRO~V243198088~C42066~R0~OB0~P4R0H~N/0/115013665/117376357/117376400/117376406/34853741/34865608/34866115/129116488/129116498/119131069/119131072
The radio displays the outside air temperature value that it receives from the HVAC control module through a class 2 message. The scan tool has the ability to update the displayed ambient air temperature. The outside air temperature value is displayed or updated under the given conditions:

Sunload Sensor
The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The 2 sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Low reference and signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts . The HVAC control module converts the signal to a range between 0-255 counts.

The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright, or high intensity, light causes the vehicles inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If sensor is open or shorted, no sunload condition occurs.



There's some reading material for ya, straight from ALLDATA. That information is based on a 2006 Pontiac Grand Prix GXP with the automatic climate control. :thumbsup

[LEWETHETIGER73]

Good Lord thats some reading right there!

Wifes car is the GT with dual climate control where either side can set there own temps. Is that the same as what you posted?

[BoosTT]

Good Lord thats some reading right there!

Wifes car is the GT with dual climate control where either side can set there own temps. Is that the same as what you posted?

... He specified its for automatic dual climate control. Can you set the temp and leave the controls alone or do you have the ghay hot/cold adjustment and have to manually adjust the fan speeds all the time?

[88Nightmare]

I what I posted was for a gxp but all the automatic climate controls should function the same. I'll verify that shorty

[88Nightmare]

... He specified its for automatic dual climate control. Can you set the temp and leave the controls alone or do you have the ghay hot/cold adjustment and have to manually adjust the fan speeds all the time?

I think they are all dual zone if I'm not mistaken. Difference is temperature knobs or a digital readout.


Clarifying again, the diagnostic I posted was for an 06 GXP with the digital readout controls.

[Reverend Cooper]

get to the hot water pipes that go to the heater core,get the car warmed up then turn on the heat,is the inlet to the heater core hot? if no do a thermostat and make sure coolant is full. if its hot and the line coming back out fro the core is cool or cold the heater core is fucked.

[brotherbenn83]

low coolant level
stuck open thermostat
faulty temp door actuator
plugged heater core

Check the coolant level first to make sure it isn't low, 3.8 intake gaskets are prone to leaking and that would be the most likely cause of a leak, or the water pump.

Does it have dual zone climate control? If it does and it is cold on both sides, chances are that it is not a actuator issue as they usually don't both fail at the same time.

Need any more help, feel free to get a hold of me.

Ben