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OK, I don't belong here, I am a long time Forum member but I spend all my time in the C2 forum. I am hoping the experience on this forum will direct me to a solution for my Escalade. 6.2L, 6L80 Trans problem with a U0073 lost communication with Data Bus A problem.
Quick recap, I went to pull a 6500 pound trailer with this truck, normally no problem. Leaving the first stop light after leaving home it started to take off 1st 2nd and on the shift to 3rd went into neutral, engine free spun and I let off and coasted to the side of the road. I had my Launch Scan tool in the truck so I hooked it up, cleared the codes and was able to get back on the road. As long as I accelerated softly it worked like brand new. As soon as I give it any gas to accelerate it throws the Check engine light and limp mode. Same code each time. Always fails on the 2-3 shift, I have not had it fail on any other shifts yet, just on the 2-3 shift.
I called a guy I know that owns a tranny shop. He says very common, the drum has split and is allowing pressure to escape when I load it. He said he sees this problem all the time. I pulled the trans and took it to him for a full rebuild. Had a new GM drum installed, he said they are now improved and much stronger and came with a full updated GM clutch pack. Tranny rebuilt, same Tehcm used in the new tranny. I examined the old parts, I did not see any sign of tranny failure in the parts. Get it back on the road and exact same issue. Now I figure this is electrical, maybe, and I better chase all the wires before buying a new Tehcm and getting that programmed.
Trace all the wires, actually replaced the Tehcm connector because it felt loose to me. Checked all voltages. The Can system tests 61 OHMS each and every time, shaking all wires or not, 61 OHM steady. Checked all my powers and the ground, used a 5 amp test load on the wires looking for a weak link. Pin 4 has 12V battery power all the time. Pin 9 the wake up power comes on with the key. Pin 9 only shows 11.8V but that is key on so there is drain from all the systems with the engine off and key on. Nomal??? I don't know.
Pin 12 is another 12V positive pin at the Tehcm, this one has 12V positive but only 12.1V again testing with Key on to activate. So, my tests show all 3 powered wires have 12V or close to 12V engine off. With a battery charger hooked up I do see the higher charging voltage at the pins. I chased all grounds I could locate, removed, cleaned and re installed. Working under the dash at the BCM, Body Control Module I wiggled and checked all these connections and went for another test drive. Previously if I gave it partial throttle to accelerate, maybe 25-35% throttle it would kick into Limp Mode each and every time. Now on test drive I was able to drive it hard, 50-70% throttle with no Limp Mode, it ran and shifts great? So I try harder accelerations, at 70-75% throttle which is moving this rig pretty hard shifting above 5,000 RPM it trips the Limp mode and code 0073 again.
Since it is always a lost communication code I wonder if it is losing 12V to one of the 3 pins, 4,9, or 12 or maybe the ground is lost at pin 5? Maybe one of the Can Bus wires is shorting out?
Maybe the engine twist under heavy throttle is causing the wires to touch, rub or stretch causing this issue??? Motor mounts appear to be OK, I have not seen any engine movement to be concerned about. At this point I don't trust it to drive anywhere. Can Bus wires tested good for OHM's and also voltages. High side was 2.6 or so, Low was 2.35. Looks normal.
I am hoping someone has walked this road and can direct me towards a solution. Thanks Mark ( sure makes repairs on the C2 seem like a cake walk )
PS: This Escalade was an estate sale, sat 4 years unused. I bought it for a good price because the engine would not turn over. Found it had dropped a valve seat and cracked a piston so I went through the engine, it runs like a top, power is amazing, the 6.2L is a real beast compared to the 5.3L's I have owned, now I just need to get a tranny working to make it drivable.
Last edited by Westlotorn; 07-11-2023 at 03:54 AM.
Don’t know the CAN Bus topology on the Escalade but it would be best to find someone that uses a scope to not only look at the CAN Bus but some other things where a DVOM doesn’t work…just because you see 61 Ohms and a roughly 2.5 volt bias means it good.
I am getting close to ordering a new Tehcm, or tranny module. I would just hate to spend the money and time to change that and still have a wire issue. Trying to rule it out first. The fact that the problem changed from a less than 3,000 RPM problem to now a 75% throttle problem makes me lean towards a wire issue? Grasping at straws.
If you checked ALL power and grounds then maybe a new TCM but like I mentioned I’m not sure how the bus is laid out and what a CAN A fault is…I only have Corvette info on Alldata.
I have thought about ordering a scope to check waveforms but have not yet done that. I will report back when I figure this out. The Corvette and Escalade share many of the same parts but I found the Escalade forum does not have members that turn wrenches, or far less members that do that type work.
My 2007 C6 threw that code last year, someone posted about checking the can buss connector, Fuse for the TCM and the harness connecting into the TCM. I put a new 15A fuse for the TCM even though the original wasnt blown, re-tightened all the buss connectors and the 12 pin TCM harness going into the transmission. Erased the code and has never come back since. He said he has fixed many of vettes with this issue by doing the above. Hope this helps
If you do get a scope which is really needed to diagnose the CAN network this is what CAN high (blue) which goes from 2.5 to 3.5 volts and CAN low which will go from 2.5 down to 1.5 volts looks like if good…they should mirror each other…serial data bus (DLC pin 2) green is a 0-7 volt square wave.
Thanks I was looking at the Pico scope options, looks like they offer 2 and 4 wire options for testing and reviews are very good on the Pico. Another learning curve!
Crusher, you mentioned re tightening the connectors? Did you remove the pins from the connector and pinch them before re installing or is there a good way to do this?
Thanks
Mark
Thanks I was looking at the Pico scope options, looks like they offer 2 and 4 wire options for testing and reviews are very good on the Pico. Another learning curve!
Crusher, you mentioned re tightening the connectors? Did you remove the pins from the connector and pinch them before re installing or is there a good way to do this?
Thanks
Mark
No I didnt remove the pins, I just re-seated all the connectors and made sure everything was tight and not loose.
Thanks I was looking at the Pico scope options, looks like they offer 2 and 4 wire options for testing and reviews are very good on the Pico. Another learning curve!
Crusher, you mentioned re tightening the connectors? Did you remove the pins from the connector and pinch them before re installing or is there a good way to do this?
Thanks
Mark
Pico offers 2 and 4 channel scopes and they are the “Gold Standard”…learning curve not very steep…many YouTube videos on their use….the 4000 series have a 200 volt max input but I believe the cheaper 2000 series are 20 volts so would just need to purchase an attenuator which are pretty cheap.
Thanks for all the help. I went ahead and ordered a new Tehcm and valve body today. I may still order a wave form tool, it seems you need them to diagnose any modern car problem. I will report back once the new Tehcm is installed and programmed.
Final Wrap, got the new Tehcm, actually a rebuilt from Street Smart in Florida, they advertised a complete rebuilt tehcm at very reasonable price $280 with a 3 year guarantee, for an additional $130 they included a rebuilt shift body. My 6L80 only had problems on the 2-3 shift and I did not know the cause so I bought both parts. They will fully program it for another charge, I think it was about $100.
On install I had questions, I wanted to make sure I was following their instructions exactly since I want this to work. They provided nice instructions on how to start up the new Tehcm, about a 20 minute procedure on your driveway before a first test drive. They answered the phone each and every time, I had multiple people help me, each one was very qualified and answered my questions right away with confidence.
I was wondering if my scan tool was giving me accurate information and if I was really ready for a test drive. The scan tool was showing the trans temp was -40* on start up and after the first 20 minute program to burp all air out of the system, so I was thinking it was a bad unit. I called they answered. Went on the test drive at their instructions and the scan tool temp started reading exactly correct as they said it would. FYI: as we were discussing the issue they right away said they could send out a replacement unit for me if this proved bad. They had me drive it on a 5 mile test with specific test instructions and it passed each one perfectly after the tranny reset was done by my scan tool. Had to verify the Manual shift was working, speed sensor was working, lock up converter working, Tow/Haul mode working. All Tested perfect.
Previously my tranny would jump into limp mode when I gave it more than 35% throttle on the 2-3 shift. I tested this at about 80% throttle and it worked fine after giving it at least 20 stop and go cycles to let it learn normal shifting. As with other 6L80 resets I have done these shift really wonky at first, slipping between each gear and then they settle down and get better and better as they learn. Most say it takes 200 miles normal driving to tune one of these. I phoned them with the success and telling them it was shifting perfect. They instructed me to go back out and stand on it. Give it a full throttle test and make damn sure it was correctly functioning. It passed that test perfectly also. It works just like it should but I was so impressed with the service and follow up at Street Smart I wanted to give them a shout out. Dorman rebuilt units are $500, there are a few other companies about that same price. This one works as it should with a 3 year warranty and quality customer service. I could not ask for more at this point. They do not charge a core charge unless you don't ship the core back within 2 weeks of your new unit arriving. They also paid freight both ways and included the return shipping label with the package. They programmed my Vin into the new Tehcm, my engine started as soon as I had everything hooked up. No additional programming needed except for the trans Re set you need to do prior to the first drive with a scan tool. I have a Launch X431V+, unit with 2 way functions that did this no problem. Hope this helps.
PS: I did purchase the oscilloscope mentioned in post #11, I still need to learn to use it properly. tried it on two cars so far and on both it reads 2.3V to maybe 3.1V on the high side can bus but the low side switches to 200 mv scale and reads much smaller voltage. I have not figured out what causes that, I tried a friends scope and it read exactly the same way. On the 200 mv scale it shows a similar wave patter to the 1st probe which is showing voltage on the 1v scale. If I switch chanel 2 to the 1v scale it shows flat line so something is off but again 2 different scopes did the same on both cars I tested? One is the Escalade but I tested with the old Tehcm installed and the other is a Ford Fusion that has an electrical issue I am chasing. Any chance both cars have an issue with the low side Can Bus? The Ford does have a bad rear view camera module not communicating and the Escalade has the bad TCM.
Last edited by Westlotorn; 07-29-2023 at 02:43 AM.
Final Wrap, got the new Tehcm, actually a rebuilt from Street Smart in Florida, they advertised a complete rebuilt tehcm at very reasonable price $280 with a 3 year guarantee, for an additional $130 they included a rebuilt shift body. My 6L80 only had problems on the 2-3 shift and I did not know the cause so I bought both parts. They will fully program it for another charge, I think it was about $100.
On install I had questions, I wanted to make sure I was following their instructions exactly since I want this to work. They provided nice instructions on how to start up the new Tehcm, about a 20 minute procedure on your driveway before a first test drive. They answered the phone each and every time, I had multiple people help me, each one was very qualified and answered my questions right away with confidence.
I was wondering if my scan tool was giving me accurate information and if I was really ready for a test drive. The scan tool was showing the trans temp was -40* on start up and after the first 20 minute program to burp all air out of the system, so I was thinking it was a bad unit. I called they answered. Went on the test drive at their instructions and the scan tool temp started reading exactly correct as they said it would. FYI: as we were discussing the issue they right away said they could send out a replacement unit for me if this proved bad. They had me drive it on a 5 mile test with specific test instructions and it passed each one perfectly after the tranny reset was done by my scan tool. Had to verify the Manual shift was working, speed sensor was working, lock up converter working, Tow/Haul mode working. All Tested perfect.
Previously my tranny would jump into limp mode when I gave it more than 35% throttle on the 2-3 shift. I tested this at about 80% throttle and it worked fine after giving it at least 20 stop and go cycles to let it learn normal shifting. As with other 6L80 resets I have done these shift really wonky at first, slipping between each gear and then they settle down and get better and better as they learn. Most say it takes 200 miles normal driving to tune one of these. I phoned them with the success and telling them it was shifting perfect. They instructed me to go back out and stand on it. Give it a full throttle test and make damn sure it was correctly functioning. It passed that test perfectly also. It works just like it should but I was so impressed with the service and follow up at Street Smart I wanted to give them a shout out. Dorman rebuilt units are $500, there are a few other companies about that same price. This one works as it should with a 3 year warranty and quality customer service. I could not ask for more at this point. They do not charge a core charge unless you don't ship the core back within 2 weeks of your new unit arriving. They also paid freight both ways and included the return shipping label with the package. They programmed my Vin into the new Tehcm, my engine started as soon as I had everything hooked up. No additional programming needed except for the trans Re set you need to do prior to the first drive with a scan tool. I have a Launch X431V+, unit with 2 way functions that did this no problem. Hope this helps.
PS: I did purchase the oscilloscope mentioned in post #11, I still need to learn to use it properly. tried it on two cars so far and on both it reads 2.3V to maybe 3.1V on the high side can bus but the low side switches to 200 mv scale and reads much smaller voltage. I have not figured out what causes that, I tried a friends scope and it read exactly the same way. On the 200 mv scale it shows a similar wave patter to the 1st probe which is showing voltage on the 1v scale. If I switch chanel 2 to the 1v scale it shows flat line so something is off but again 2 different scopes did the same on both cars I tested? One is the Escalade but I tested with the old Tehcm installed and the other is a Ford Fusion that has an electrical issue I am chasing. Any chance both cars have an issue with the low side Can Bus? The Ford does have a bad rear view camera module not communicating and the Escalade has the bad TCM.
What scope did you purchase ??…maybe take a screenshot of your waveform…don’t know what you mean by “low side switches to 200mv scale” ??
Sorry, Can Hi and Can Low which should be each close to 2.5V but varying. I bought the tool in Post #11, a link is on that post.
Never heard of that brand...like I mentioned and in my #7 post CAN high goes from 2.5 to 3.5 volts and CAN low goes from 2.5 to 1.5 volts...if it doesn't look like that waveform it's bad....the long lines at the end of each data packet is "end of transmission" and is normal...video below I think you'd like...watch from the 45 minute mark.
I am aware of the can high and can low voltage range, my scope is not in range for can low. Like mentioned it is reading a signal but only on the 200mv scale. I will take a look at the video. Thanks.
I am aware of the can high and can low voltage range, my scope is not in range for can low. Like mentioned it is reading a signal but only on the 200mv scale. I will take a look at the video. Thanks.
I normally set my scope on a 10 volt scale or even 20 volts so if one of the CAN lines were shorted to power at 12 volts I’d see it...I have no idea how that scope is set up…like I mentioned a screen shot would help !!
07-11-2023, 03:48 AM
6L80 Limp Mode U0073 Code
