No comms with pcm

Ricardo Diagnostician Michigan Posted   Latest   Edited  
Resolved
Programming
2007 Buick Rendezvous CX 3.5L (L) 4-spd (4T65-E)

Hello DN , first of all I'm not doing diagnostic on this one just trying to reprogram pcm so forgive me if I didn't post any tests , the shop technicians are in charge of that. This buick is at a transmission shop, it runs and drives “good” the issue is that about 45 the tc engages/disengages, they rebuilt the trans twice with new torque converter and issue remains, so they called me to reprogram a used pcm. With original pcm car starts , runs and there's not a single code in the whole car. So plug the used pcm and as soon as the ignition is turned on , the odometer changes to “error” and no comms with pcm , every other module throws class 2 data link malfunction bad pcm right? Get a second one same issue, get a 3rd one which was removed from a running car (yeah I saw it running) same issue , 5th pcm and same issue (all with same part/service #) they decide to buy a reman , same issue. So now we're waiting on a brand new from dealer , in the meanwhile original pcm is in and car runs , drives and not a single code in whole car so hard to believe it's a wiring issue. I'm positive this is not global A and even if it was I would still have comms. I know is not a scanner issue because I'm able to read original pcm but nevertheles we tried autel, snap on, tech 2 . So any ideas on the tc issue or pcm issue will be greatly appreciated. Thank you

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Ryan Owner/Technician
Ontario
Ryan
 

Those use to have the transmission valve body issue, use to program a lot of them…. sounds like you got either a bad pcm or wrong one. A used pcm will still communicate and not put error on dash other than security.

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Ricardo Diagnostician
Michigan
Ricardo
 

Yeah that's what has me scratching my head, hard to believe 6 pcms are bad with exactly same issue. And everywhere I checked the part # matches with the original and the 5 used pcms we tried.

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Ryan Owner/Technician
Ontario
Ryan
 

I ran in to issues where they would install the wrong tecm “valve body” part number would be wrong.

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Kevin Technician
Tennessee
Kevin
 

You should have gotten a different reaction somewhere down the line. 6 PCMs all doing the same thing is extremely unlikely. The only thing that is a common denominator is the car, my guess is the wiring is bad somewhere (and the original PCM is damaged in a way that isn't throwing codes).

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Glenn Owner/Technician
Texas
Glenn
 

Hi Ricardo, Sounds like a physical problem with the convertor or the convertor activation solenoid. Programming does not fix a physical problem. They need to do a full pressure test with gauges and actually diagnose the problem. That it is why the tranny has pressure test ports. What are they calling new? I question if they went through the valve body assembly properly. Some require a new valve…

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Ricardo Diagnostician
Michigan
Ricardo
 

I agree with you, I'm pretty sure too is not an electrical/software issue and I don't know what they install when rebuilding the trans but what has me scratching my head is the pcm issue , hard to believe 6 bad pcms with exact same issue .

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Interesting
Jose Technician
Illinois
Jose
 

Looking at the communication bus diagrams for a 2007, I see there is only a class 2 data line to the pcm, where a 2006 pcm has both a class 2 data pin and GMlan pins. I would try to get to the splice pack and isolate the pcm to see if communication is restored. Then add modules back on until the communication is lost.

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Kerry Mobile Technician
Ohio
Kerry
   

For what it's worth, I encountered a similar situation on the same vehicle. It was a 2007 rendezvous and the customer had procured a used PCM for us to flash. We had no communication with it. There was no communication with the original one and that was why it was being replaced. They ordered a 2nd module from the salvage yard and that too would not communicate. We told them we would bring a…

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Helpful
Scott Owner/Technician
Michigan
Scott
   

around this era gm was transitioning from class 2 to can have seen several that had issues like you describe. issue is the gm service/reman pcm fits either application as the “base file/dummy calibration” that is loaded on the unprogrammed pcm will communicate with either class2 or can once programmed to a specific vehicle the pcm will only communicate on that vehicles network…

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Kerry Mobile Technician
Ohio
Kerry
 

Quite true Scott, I've confirmed this once or twice by building the vehicle on the tech2 based on the donor versus the receiver and have seen a difference in base communication

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Jared Diagnostician
Maryland
Jared
 

Verify that it was indeed DexronVI used to fill it. I have had alot of TCC issues during partial apply that was directly caused by universal synthetic fluids on these years.

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Raymond Mobile Technician
Michigan
Raymond
 

Hi Ricardo , in reference to the data issue Im with Jose I would Like to know if u can get to sp205 and disconnect splice comb and only hook up Pcm and scan tool so now u r leaving every other module out of data bus and see if u have comms. Man I find it hard to believe that all 6 modules r doing exact same thing , also there is a splice pack 206 which goes to that problematic VCIM (vehicle…

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Raymond Mobile Technician
Michigan
Raymond
 

Hey Ricardo I’m getting OEM wiring diagram for that vehicle and like some of the guys mention there r different wiring some Ecm use class 2 and some mite have strictly CAN for Pcm and Tcm and class 2 for everything else , so my question is what pins r at DLC ?

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Raymond Mobile Technician
Michigan
Raymond
 

Hey Ricardo I been thinking, the vehicle u said u saw it running and tried that Pcm. can u compare all the pins match in DLC ?

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Raymond Mobile Technician
Michigan
Raymond
 

hi ricardo, sorry bout all the questions, but u mentioned flash programming a used pcm, I want to know if u had any issues with the SPS2 system , I getting different answer about flashing used modules, have u had success with used modules non global A vehicles in the past with new a/c delco system?

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Ricardo Diagnostician
Michigan
Ricardo
 

Hey Raymond sorry for late answer but so far I haven't had problems programming used modules with sps2 , I have been able to program used global A modules too except ecm .

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Ricardo Diagnostician
Michigan
Ricardo Resolution
 

Thank you everybody for your ideas the brand new pcm from dealer took care of the comms issue I guess same part # can be programmed for different communication systems like some of you explained . They will let me know if it took care of the trans issue but doubt it. Thanks again everybody for sharing I learned something new.

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Jim Owner/Technician
North Carolina
Jim
 

Ricardo, I had a similar situation a few years ago, after 3 transmissions and several ECM's, I was called to look at it. The thermostat had been removed, and it caused the torque convertor to unlock, lock up as it cooled down and heated back up. HTH

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