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Chev Aveo LT: A/C not cooling & Intermittent sensor fau

have a 2010 Aveo LT...

have a 2010 Aveo LT. history of intermittent temperature sensor faults (don't remember code) temp gauge also refused to move a time or two but no issues with operation at all. usually noticed these issues after i changed oil (bumping wires? or sensor?) then finally paid for oil change at Pep Boys yesterday, and since then temp gauge has failed to move at all. and noticed today A/C would not cool (?) not at all. doesnt seem to respond to the control even though all knobs and lights seem fine. any ideas?  (note: no engine fault light at this time) has been couple months since CE light was on for that sensor. 

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Answered in 4 hours by:
9/27/2013
Technician Chris
Technician Chris, Technician
Category: Car
Satisfied Customers: 425
Experience: I am a certified ASE Master Technician with L1 Advanced Diagnostic Specialist and over 15 years experience.
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The A/C is actually controlled by the coolant temperature sensor. If the PCM is not getting a signal from the coolant temp sensor, then it will not allow the A/C to run at all. If you have already checked connector at the temp senor, and it seems fine, then I would replace the sensor and see what happens. They are usually around $25 to $50 for the part and it is very simple to replace. Just carefully disconnect the wire connector and using a wrench or socket remove the sensor itself.
Technician Chris
Technician Chris, Technician
Category: Car
Satisfied Customers: 425
Experience: I am a certified ASE Master Technician with L1 Advanced Diagnostic Specialist and over 15 years experience.
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Customer reply replied 4 years ago

Thanks for the answer. just for the record, i checked the connections of plugs and connectors before leaving work today. (still not clear on actual location of this sensor) about a mile down the road, the temp gauge jumped up and started working and the A/C went cold immediately. this intermittent thing really leaves me suspecting a loose wire (in connector plug?) for this switch vs. sensor being bad. works for months at a time with no CE light then faults a few weeks and works a few weeks.

graphic

graphic

So I did some digging in the repair manual for your vehicle. Apparently there are 3 coolant temp sensors in your car. Most vehicles only have 1. The 1st one is located underneath the intake manifold and plugs into the coolant distribution block. The 2nd one will be relatively easy to access. It is located on the bottom right (passenger side) of the radiator. The 3rd one, however, in located in the heater core which is behind your dash. This you may not be able to access. Start by checking the connectors at each sensor and if all is tight, then try to trace the wires to find any kind of frayed or loose connection.

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Customer reply replied 4 years ago

Thanks for the research and the assistance. 1 more follow up. is it possible to determine, which sensor sends signal to Temp gauge. and which sensor triggers Check engine light? temp gauge unresponsive, never turns on the CE light. CE light never seems to interfere with A/C operation.

The sensor at the coolant distribution block is the "main" one, and the one at the radiator is a back up. The one in the heater core only effects heater function. In order for the check engine light to come on, both sensors have to fail for 2 cycles. (start vehicle, drive, then shut off vehicle is 1 cycle) The one at the radiator is a back up and being the fault is intermittent, the light never comes on because the sensors aren't actually bad, but rather the connection between one or both of them and the PCM just comes and goes. If you scan the computer for codes, I would bet you will find stored codes or "soft" codes related to the sensors. The PCM will detect the fault immediately, but won't turn on the light until after 2 complete cycles of fault detection.
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