2009 Chevy C4500 No Communication With Tcm

Mike Owner Cromwell, Kentucky Posted   Latest  

first time poster, been lurking for some time. the truck in question came in with no comm and all powers and grounds are good. the original tcm would light up the prndl in dash but wouldn't comm. and took off in high gear. it had a good 7 volt square wave at pin 2 of dlc and it mirrored what was at pin 46 at tcm. so I ordered new tcm and programmed it with my pass thru. it wouldn't comm. afterwards and wouldn't even light up the prndl. so I ordered second tcm from gm thinking I had bad one (had a couple over the years). it, too, wouldn't comm. and wouldn't light up prndl. so I started tracing wiring and found 3 different places the harness was shorting to ground and the ebcm had the power wire and one comm. wire damaged with green death inside. after repairing all wiring that I saw, I reconnected my original tcm and it worked good for about 20 minutes of driving. then it would go into limp again and not communicate with scanner. I've checked the signals at jx203 and all wires have good 7 volt square wave and mirror what is on pin 2 at dlc. I disconnected everything at the jx203 connector and jumped out tcm, pcm and dlc pin 2, and it made no difference. after it cooled off and it sat for while, the tcm started comm. again and after several miles, it once again quit talking. i'm at wits end with this one, wondering if I've got bad original tcm and 2 bad new? when I hook up the pass thru both of the new tcm's show the correct programing. i'm open to any suggestions, appreciate everyone on here. thanks.

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Michael Diagnostician
Irving, Texas
Michael Default
   

Have you tried to jumber the Ignition Circuit at the TCM. Battery voltage to Ignition Circuit at the TCM. B+ Pin 10, 70 IGN Pin 63 GND 9, 69 Also, would check for a voltage drop.

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Mike Owner
Cromwell, Kentucky
Mike Default
 

yes, I load tested all of the wires mentioned with a bulb and they all were good. also forgot to mention, it has 60 ohms on pins 6 and 14, but i'm told it doesn't use can bus on this engine, only class 2 serial data (it's hydraulic brake vehicle, not air brakes). another thing I forgot, when I ping all modules, the ebcm doesn't ever show on scan tool that it's an option and when I have my pass…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi Mike. More information would be helpful, VIN # engine and transmission series If it is the LCT series transmission, there are two designs of mode switch for transmission gear selection, depending whether 5 speed or 6 speed. I haven't worked on a C4500 since 2005, so my reference is based on model year LCT 1000 changes in pickups. 5 speed LCT 1000 used the external NSBU switch (same as on…

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Mike Owner
Cromwell, Kentucky
Mike Default
   

sorry, thought the vin was included near the title, 2009 c4500 8.1 liter Allison 2000 with hydraulic brakes. vin #1gbe4c1g39f408322. this one has the internal mode switch. I too see these bad a lot, but don't think this is the problem here. I included the prndl lights part because the original tcm lights up the prndl lights correctly even when it has no comm. but both the new gm tcm's never…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi Mike. Do you have a Tech 2 or Tech2WIN to scan the system with? The truck has both Class 2 and HS GMLAN communications and you may be missing something. The Tech 2 will poll the modules and prioritize DTCs and identify the affected network DLC pins. The other thing is that you mentioned that the EBCM doesn't communicate. Since that is on the HS LAN and you have 60 Ω on the network, the bus…

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Mike Owner
Cromwell, Kentucky
Mike Default
 

I do not have the tech 2. I have all snap on scanners and the only thing I have with hd capabilities is an autel. with it I tried pinging all modules and it never shows the ebcm and when I have the pass thru hooked up it doesn't show option for ebcm? I normally don't get into anything this large, but got in deeper than I planned on this one.

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Mike Owner
Cromwell, Kentucky
Mike Default
 

so, i'm a little confused. I was told early on that this truck doesn't use the can bus (pins 6 and 14 at dlc) for tcm communication. (because it is an 8.1 and not diesel) when I scope it, I don't get a good waveform. can high goes from 2.5 to 3 volts (and not good waveform) and can low stays at 2.5 and don't go low at all. I've concentrated on the class 2 communication due to the advice I…

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Michael Mobile Technician
Clinton, Utah
Michael Default
 

Hi Mike, I had one of these I worked on a while back with a similar situation. A couple of items that may help you. Instead of trying to find the problem on the class 2 wiring between the TCM and splice pack, We overlayed a new wire to the TCM. The one we had was an Allison. The TCM had to come from a MD GMC dealer, The hardware part number was different from Light Duty vehicles even though the…

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Mike Owner
Cromwell, Kentucky
Mike Default
 

thanks for the input gents. when I hooked up my pass thru, I only had one option for the programming for this particular vin number? (possibly because it's the 8.1 liter) it was the same programming number as my original tcm had? the odd thing is, the pass thru showed it programmed fine, however, neither of the new ones would ever communicate. the original does intermittently communicate.

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Stephen Educator
Bethel, Ohio
Stephen Default
 

One thing to consider here. You said the transmission functioned properly until it warmed up. At that time it would no longer communicate and would go into limp-in mode. (correct me if I'm wrong) If you look at the transmission wiring diagram you need to determine if the sensors and solenoids in the transmission are powered through the TCM. If this is the case, it is likely one of these are…

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Mike Owner
Cromwell, Kentucky
Mike Default
 

thanks Stephen, at times, the original tcm will communicate, not always though. this morning it won't comm. even though it's sat all weekend. when it does communicate, it will for roughly 20 minutes and then it will stop talking and everything goes into high gear, prndl lights quit working and only code generated in the pcm at that time is the p0856. when I ping all modules i'm never seeing the…

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Mike Owner
Cromwell, Kentucky
Mike Update
 

update; this morning, on second try, I was able to get tcm and pcm communication. when it was communicating, i did have a good waveform on can bus, and once it quit talking it went stupid again. when it was talking i still didn't see an option for abs communication? after roughly five minutes of idling, I lost communication with tcm, and now, pcm, although the engine still starts and runs fine…

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Michael Diagnostician
Irving, Texas
Michael Default
 

If power, ground, and communications are good, I would monitor communication with GM's Data Bus Diagnostic tool. Also, I would do a terminal drag test on the connector. I made the mistake of back probing a connector to deep and spreading a terminal and having some wild readings.

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Stephen Educator
Bethel, Ohio
Stephen Default
   

You need a wiring diagram. Find the power feed for the transmission solenoids and sensors. Most likely you will find the TCM provides the power and ground. When the vehicle is acting up, check for ignition voltage to the solenoids and sensors. If voltage is not present and the TCM isn't communicating, the TCM is shutting down to protect itself. If the power is being supplied from another source…

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Mike Owner
Cromwell, Kentucky
Mike Default
 

so I've done pin drag test on all pins in tcm, all good. I've monitored the voltage at tcm. my fused b+ feeding tcm is good. initially, I had good power feed from tcm to trans, but when it quit talking, it shut down the power feed to trans. I checked resistance of all internal trans components from tcm connector to trans and all resistances were good. at times, it's also causing the ecm to shut…

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Stephen Educator
Bethel, Ohio
Stephen Default
 

Did you do a complete scan of all the modules on the vehicle? It could be the problem is being caused by another module or some kind of EMI. Again, I have no wiring diagram for this vehicle. Does it have CAN? If so, have you checked that network? What other networks interact with the TCM? Also, when the ECM stops communicating with the scan tool have you tried hooking up a scan tool that will…

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Mike Owner
Cromwell, Kentucky
Mike Default
 

I borrowed tech 2 from another shop yesterday, and it was same as the autel..…...I'm pretty certain I figured out issue tho. I talked to a programmer that does a lot of these with efilive as well as factory programming. apparently, the new tcm that gm sells is a t14 and gm never updated their Allison software to replace an a50 (which is what came off of it) with an t14 computer. (and all they…

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Bob Diagnostician
Vitebsk, Belarus
Bob Default
   

The can comm you saw could have been just between scantool and tcm. I think you could check for 5v ref at the tcm and find which wires share 5v ref and the current going through each of these wires. Perhaps 5v will be lost while no comm condition, but then you can check current again or even cut the wires and check if it resumes communication. And how about just connecting power ground and comm…

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