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2003 Cadillac CTS
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18 Posts
Discussion Starter #1
Got a 2003 CTS and I just had the thermostat and housing replaced to fix the P0128 code. Heat before wasn't that great, but now the heat on the passenger side is decent but the heat on the driver side is almost nil. Temp is set at 90 for both sides. Is this likely a cooling system problem, or is this more likely an electronic problem? And so far the code hasn't come back. Thanks in advance for the help.
 

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2004 CTS luxury package
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300 Posts
I was just talking to the service advisor about this kind of thing today. There are three mechanisms in the dash that control the vent and damper doors. Odds are that one of them has gone out on you.

I believe they're called air vent dampers. If they malfunction, you will not get the desired temperatures. There's a separate one for the driver, and for the passenger. The third one, I'm not sure yet.
 

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03 CTS 3.2L (Sold) / 09 CBR 600rr /2014 GMC Sierra
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7,872 Posts
heater core is clogged.
passenger side feeds the heat from the top half, drive side vents get heat from bottom half of the core.
 

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2003 Cadillac CTS
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18 Posts
Discussion Starter #5
Great - thanks for the tips. I'll give the heater core flush a try first since that sounds easier. If that doesn't work I'll get looking at the air vent system.

I just bought this car so I was bummed to have the P0128 code, but with that fixed the only other problems I have to address are the above heat issue, the rattling sunroof and the seemingly bad struts up front. Glad to have found this forum. Looks like I'll be spending some time reading more here. Thanks again for the help.
 
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