P0128 - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
Problems and Service Talk about any mechanical problems you are having

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post #1 of 12 (permalink) Old 11-01-2016, 07:21 AM Thread Starter
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P0128

Hello everyone. The other day my CEL came on and had the code P0128 which I am familiar with from about 2 or 3 years ago when I replaced my thermostat with an AC delco thermostat. When the light came on my coolant temperature wasn't reading above 180 F I don't believe. I'm sitting at idle right now after some driving and my coolant reads 189 F and the outside temperate is 36 F.

Does it sound like I need to replace my thermostat again?
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post #2 of 12 (permalink) Old 11-01-2016, 07:29 AM Thread Starter
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I forgot to mention that my coolant level in the expansion tank is above the cold fill line and I don't have any driveability issues. 2005 Cobalt 2.2L base automatic
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post #3 of 12 (permalink) Old 11-01-2016, 07:48 AM
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I'm sure you already know what that code is, but for anyone else looking at this thread later on, here's the English version:

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Originally Posted by XFE View Post
P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature
My guess is that replacing the thermostat would probably clear up the issue. I'm a little surprised that yours is going out so frequently since I've never replaced mine and it's been going strong for ~6 years. How many miles have you racked up?


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post #4 of 12 (permalink) Old 11-01-2016, 08:07 AM Thread Starter
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A little over 120,000 miles
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post #5 of 12 (permalink) Old 11-01-2016, 08:14 AM
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That code means your engine didn't reach operating temperature in the pre-set delay. This means your thermostat isn't closing tight or the rubber seal has failed.
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post #6 of 12 (permalink) Old 11-01-2016, 12:29 PM Thread Starter
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Quote:
Originally Posted by Coby7 View Post
That code means your engine didn't reach operating temperature in the pre-set delay. This means your thermostat isn't closing tight or the rubber seal has failed.
The last time this happened I replaced it with an AC Delco stat. Should I look into a different one?
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post #7 of 12 (permalink) Old 11-01-2016, 04:26 PM Thread Starter
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The CEL turned itself off. I'll see if it comes back on.
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post #8 of 12 (permalink) Old 11-08-2016, 11:06 AM Thread Starter
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The light hasn't come back on yet. Hmmmm
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post #9 of 12 (permalink) Old 12-03-2016, 07:17 AM Thread Starter
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$230 later it's all fixed.
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post #10 of 12 (permalink) Old 12-03-2016, 07:32 AM
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What did you do???or get done.

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