Hi, If I turn my 2010 GMC Terrain on , the heat

DTC C0545 00: Steering Wheel Torque Input Sensor


You need service repair info. for diagnostic testing for code co545.
Circuit/System Description
The power steering control module (PSCM) continuously monitors the torque sensor input and output shaft sine wave frequency signals. As the steering wheel is turned and torsional twist is applied to the steering column shaft, the torque sensors input and output shaft sine wave frequency signals are processed by the PSCM to detect and calculate the steering torque.

Conditions for Setting the DTC
The PSCM detects open, short to ground or short between any of the torque sensor circuits.
Actions Taken When DTC Sets
• DTC C0545 is stored in memory.
• The driver information center (DIC) displays the SERVICE POWER STEERING warning message.
• No steering assist.

you have a air lock...Start the car with the radiator cap off. One of the easiest ways to bleed your car's radiator is to simply remove the radiator cap and then start your engine. Leave the vehicle running until it reaches its normal operating temperature. It may take between 15 or 20 minutes before your car generates enough heat to push out the air that has been trapped in your car's cooling system. You may find that you need to add additional coolant, as air pockets can artificially inflate coolant levels.
hope this helps

There are no grease fittings on the 2010 GMC Terrain.
The only items you can apply a thin film of white spray lithium grease are the door, hood and rear hatch hinges.

Have you checked fuses ? Might be your actuator. Does the heater motor run at all ? Are you getting any cold air at all ?

Check the video on the below link:
https://www.youtube.com/watch?v=C4ZrksFQwag
GMC Terrain Camshaft Position Sensor
http://workshop-manuals.com/gmc/terrain_fwd/l4-2.4l/transmission_and_drivetrain/transmission_control_systems/sensors_and_switches_transmission_and_drivetrain/sensors_and_switches_a/t/transmission_speed_sensor_a/t/component_information/locations/page_7020
GMC Workshop Manuals

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It's POSSIBLE, although it may or may not be true. Is this a continuous knocking noise with the AC running, or does it just knock a few times, then stop? If it's continuous, does it change in speed with the engine speed?

At any rate, that vehicle SHOULD still be under warranty; the dealer should be taking care of all of that for no charge.

Is it the heater fan making the noise? Some can be lubricated, others have to be replaced. I hope this is helpful.

if your radiator is not full of anti freeze (water) their is nothing to flow through heater core to make heater work.

It has a fuse, but may not be listed on the fuse panel. Your owners manual should have a complete list of every component on each fuse circut.