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2003 CTS
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43 Posts
Discussion Starter #1
I have a 2003 CTS that has about 149k on it. I keep getting a code that comes up P0128C. It comes up on my dash screen and under the "ECM" codes.
Also on the same front under the DDM codes I get U1714H, any help on these 2 codes would be helpful to me.... I do know the H is history code and the C is current. Since they both still come up from time to time (and its cold as all hell here in Ohio) should the H one i be
concerned about or not? I have also been told at the mileage I am at that i should have the radiator flushed, any particular coolant should be used.?? According to the manual it states DexCool 50/50 mix. i have read on here some say yes and some say no. Any thoughts??

thanks in advanced for any help anyone can provide me....
 

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2003 CTS
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43 Posts
Discussion Starter #3
Thanks Tom's Caddy... Do you have ideas on the codes i posted by any chance too??
 

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2003 CTS 1SC Luxury Sport
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1,017 Posts
P0128 is thermostat below regulating temperature and the other is a communication error. Wouldn't worry about that one. More than likely you need a thermostat, also check the heater by pass valve and vacuum lines to it.
 

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2003 CTS
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Discussion Starter #5
I just put on a new thermostat about a month ago and had the heater core flushed. Tomorrow I think I'm going to have the radiator flushed. See if that helps. Would that make sense??
 

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2005 CTS/ 2008 DTS/ 2008 STS V8 N*/ 2011 CTS4 ALL W/D Pearl
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688 Posts
I just put on a new thermostat about a month ago and had the heater core flushed. Tomorrow I think I'm going to have the radiator flushed. See if that helps. Would that make sense??
If you did not have the P0128 thermostat code before you changed it out, that's the problem and is very likely what jran0823 said about the bypass valve.

The U1714 was for a front door window module.
 

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2003 CTS
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Discussion Starter #9
so what do I do? do I bleed the unit using the heater bypass valve, and if so what steps do I need to do? tried to find some info online and couldn't find an exact definition on this..... thanks to anyone who can help me.
 
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