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post #1 of 8 (permalink) Old 09-12-2012, 02:28 PM Thread Starter
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09 Cobalt Ls Overheating

i have a 2009 cobalt ls 4 door.
when i was driving from work yesterday the car started to overheat it reached temp 257F. the cooling mode message came on on the cluster panel but the fans did not turn on.
i've checked the fan fuses and their ok.
what could be the problem
the fan does turn when i run the A/C.
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post #2 of 8 (permalink) Old 09-12-2012, 02:44 PM
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post #3 of 8 (permalink) Old 09-12-2012, 03:10 PM Thread Starter
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can the thermostat cause the fan not to go on?
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post #4 of 8 (permalink) Old 09-12-2012, 03:17 PM
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Yes, if the therm doesnt think its too hot the fans wont turn on.


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post #5 of 8 (permalink) Old 09-12-2012, 03:29 PM Thread Starter
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ok ill replace the thermostat.
anything other ideas what to check for?
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post #6 of 8 (permalink) Old 09-12-2012, 05:09 PM
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Well I hate like hell to disagree but I'm going to anyway. First thing you should check, and I assume you did, is the coolant level. The thermostat itself has nothing to do with turning on the fan. You said earlier that the fan comes on with A/C so this eliminates fan speed 1,relay and fuse. The two fan speeds are determined by coolant temperature. The PCM commands Low Speed Fans ON under the following conditions:

• Engine coolant temperature (ECT) exceeds approximately 106C (223F).

• A/C refrigerant pressure exceeds 1 310 kPa (190 psi).

• After the vehicle is shut off, the ECT at key-off is greater than 140C (284F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The PCM commands High Speed Fans ON under the following conditions:

• ECT reaches 110C (230F).

• A/C refrigerant pressure exceeds 1 655 kPa (240 psi).

• When certain DTCs set

Now with this said you know your coolant temperature sensor is working because you could read 257F right. So why didn't the fans come on? Something failed with your ECM because this is the module that turns the fans on. You either have a burnt fuse or a broken wire or bad connection somewhere that prevents the "ECM" from receiving coolant temperature readings.

Myself I would do a fan test with a TechII to verify if these work properly first, if so I would then clean the two ECM connectors and re-install. If this fails to fix the problem I would then attempt to find why the "ECM" is not getting the temperature reading.

Might even be your water pump that has seized and not circulating coolant.
Thermostat don't usually just close shut all of a sudden in fact the big problem with Cobalt thermostat is that they don't close enough as they get older.

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Last edited by Coby7; 09-12-2012 at 05:12 PM.
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post #7 of 8 (permalink) Old 09-13-2012, 05:56 AM
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Good morning 09cobaltls,

You've gotten some great feedback already; if you decide to work with a GM dealership on getting this looked into, or if you wanted for me to check into warranty or recall information for you, please feel free to contact me via private message (include the last 8 digits of your VIN and contact information).

Sarah, GM Customer Service

Last edited by Coby7; 09-13-2012 at 09:07 AM. Reason: 09cobaltls not 08cobaltls
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post #8 of 8 (permalink) Old 09-14-2012, 08:08 AM Thread Starter
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thanx for some great info Coby7
so i double checked the fans relay with the battery n they work. i also cleaned them a bit and i replace them back n now the fans kick in between 225-230F
so it should be ok for now.
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