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I have a question that 3 days of SEARCHING has not answered. I am hoping a GM tech will read and respond to my problem. Here it is. I purchased a 2006 Chevy Impala in December of 2013. The dreaded 6T70 trans wave plate broke(first generation trans). Had it replaced at a Chevy dealer with a GM "SERTA" trans(updated internals I hope). 3 weeks later, the PCM lost communication with the TCM(Transmission Control Module). My car went into LIMP-MODE, reduced power and all that. Everything I read and ALL the pictures I saw, showed the TCM internal to the trans valve-body assembly. Expecting this to be covered by the GM "SERTA" trans warranty, I was disappointed to learn that it wasn't. Instead of an internal TCM going bad, it was external, by the PCM, under the air-box. The dealer replaced with a new one and programed it for $600. Ssoooo.... there are 2 TCMs? One internal and one external(in addition to the PCM)? Was there a design change? What am I missing here? The odds of a trans problem seem TWICE as likely(and expensive) now. Thanks for any help with my lack of information and I am sure other people would like to know. :WTF:
 

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The 6T70 transmission only came to the Impala's in the 2012 model year (although it was in the certain Chevrolet Malibu's and SATURN AURA's beginning in 2007 model year). The 2006 Impala's threw 2011 have the 4T65E transmission. The 4T65's have an external TCM.
 
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