ABZ Vette

I have a long term problem with loss of GMLAN comms and was hoping solve it without sending the car to a dealer as the car is in the North of Scotland in limp home mode and nearest dealer is 600miles south.

I posted on this problem in April and Bill Dearborn was helpfull but needing fault codes to track down the problem.

I have been working overseas a lot this year so basically the car has been parked for the whole summer.

Have DIC "service traction control" but the only code I can read is U0101 "lost communication with TCM". I figure it is a plug come loose but where to look? I did go out and buy a Scan tool Scan XL with the latest GM add ons but again it only read the one code U0101, lost comms with TCM.
The car was going a long fine, suddenly lost power, gauges did a sweep and dash background light cameon and off. Now stuck in 3rd gear only and no throttle response. Will just make it to 2000rpm but won't climb hills. Engine idiot light is on and another to do with locking and security. Traction control button does not switch off traction control. I have read widely about the usual faults and have checked battery, leads and all earths to the frame. Tried deleting the code (only U0101 showing but I know it has previously had DIC "service tyre pressure montor" so was expecting to find more fault codes. Read yesterday on another forum "Smokinvettes", about Talon 90's impressive data on TSB's for 08 vette and see a lot with U0101 codes to do with a loose plug on the transmission harness or onto transmission, eg. 13 TSB No.:08-07-30-021 NHTSA No.:10025402 TSB Date: April 1, 2008 Date Added to File:August 6, 2008
Failing Component:
Digital Instrument Panel
Summary:
Loss of high speed gmlan communications, intermittent no crank, ipc gauge fluctuation, intermittent door lock cycling, transmission may not shift, DTCs U0073, U0100, U0101, U0102, 70140 (repair backed out terminal in transmission harness).

I see also that Bill has a complete list of TSB's for his car and again the loss of comms comes up on TSB 08-07-30-021b

Can anyone tell me where to look for this potentially loose plug and does this apply to 06 C6. It is also due recall for steering column wiring harness plug fault in telescopic steering colum. Any one got photos of this plug so I can identify it and eliminate it from the search.
Any help for a newby greatly appreciated.

tjwong

Attached is a PDF file that shows the right side of the transmission, it is item 3. This very problem can apply to any C6. Lan failures are not very common but do occur from time to time and can ba a PITA to diagnois even for a seasoned GM tech. I have also added the lan diagrams for the PCM, the GM LAN diagram and the TCM LAN.

Z06Ronald

Is there a website where one can download attachments like yours?

Bill Dearborn

I can't remember our conversation from back in April or whether I sent you a copy of the TSB. The TSB does have pictures showing the connector and where it is located and how to open it. TSB was written for 07-09 Vettes but it may apply to your car as well since you have the same transmission.

Here is the TSB:





If you want a clearer copy send me a PM with your email address and I will send a MS Word version.

If you need to use the Kostrel Connector repair information referenced above send me a PM or post in this thread and I will copy that info as well.

Bill

tjwong

There is a website but you have to be either a GM dealer or have a paid subscription via AC Delco to have access.

Z06Ronald

Ah, okay I see ...

Bill Dearborn

If you have the DVD with all of the GM Service Manual info covering all GM cars from 97-09 a fair amount of that stuff will be in there. Definitely the schematic, the transmission diagram is probably in there as well but would take some searching. Theories of Operation are in each section of the manual along with more detailed info in each diagnostic procedure.

Bill

ABZ Vette

Guys, I am impressed by the info you can lay your hands on. Many thanks Bill and TJ. I will get back under the car armed with this new info and see if there is indeed any backed out terminals. When I last looked I did not even see this horizontal connector. I did see a vertical connector on the rhs at the rear of the transmission (facing down into the pan) but this may not be the one. Looks like this one is on the back end of the casting that connects to the sump pan.
Any tricks on opening the connector? Most have a tab you need to release. Easy if you have seen one before but can be fun under the car for the first time. Do you need to remove the exhaust to get at this connector?
Do you think I may be on the right track? It was just the sheer number of similar TSBs for this terminal fault that have led me in this direction.
There were about 6 similar TSBs in Talon 90's list for the 08.
I can email you the list if any use. How do you send a PM?

I would still like to get a hold of similar pictures showing the terminal fault in the steering column so I can sort and eliminate this fault as well.( I'm guessing but would the steering column fault show other fault codes?)

Many thanks, I will keep you informed of progress.

Al from Aberdeen

ABZ Vette

Guys,
Sorry but I was misinformed and my car is actually a US 05 model so the transmission is different and the electrical connector plug appears to be different also. Does any one have info on faults with an 05 that would cause U0101 fault code? Could it still be the rhs harness plug (mine is a vertical connector) on the transmission?

Any and all ideas and leads appreciated.

Al

Bill Curlee

Al

Bill contacted me and asked me to see if I could help. I'm pretty good with anything C5. I had a 06 Coupe and it had a couple of issues also.

One was the Steering Wheel Position Sensor ISSUE!

I had the dealer installed TSB (RED COMB) installed and that helped for 6 months. Then I would get sporadic Traction Control Issues. I solved that issue by removing the connector and spreading the pins inside the SWPS a minute amount. That seemed to resolve that issue.



I had another issue that was a LOT worse. When I would press the START button,, the dash would go BLANK and the only light on the dash would be the CEL.

Pressing OFF and allowing the car to sit for a few minutes seemed to allow the problem to resolve it self. A couple of times, I had to disconnect the battery short the NEG and POS battery cables together and reconnect the cables. That would get me going again.

I replaced the ignition switch but that did not resolve the issue.







Try this. Disconnect the battery for a few minutes and see if you regain all functions after reconnecting the battery.

If not, Check ALL of The TCM fuses. Use a DC Voltmeter. There are TWO test points on top of each fuse. Measure those test points to chassis ground. You should read battery voltage on each test point to ground if the fuse is good. Some fuses only have voltage present when the IGNITION is ON. Make sure that the fuses are properly powered by insuring that the circuit is ON.

If you put the POS and NEG meter leads ACROSS the TWO TEST POINTS of a GOOD fuse, you will NOT read any voltage.

If you put the POS and NEG meter leads ACROSS the TWO TEST POINTS of a BAD fuse, you will read circuit voltage thru the meter.

Do you understand that theory??

I have the GM SI Service Manual schematic program and it includes the 05 C6 schematics. We will get to the bottom of this one way or the other. I'm still learning the C6 systems and will research this as much as I can.

Bill

ABZ Vette

Bill,
Many thanks for your leads above. I primarily want to rule out the steering column wiring connector issue but do not think this is the cause of my problem as I am assuming the steering wheel position sensor issue would have its own fault code and I am getting only a U0101 code (lost comms with TCM) and nothing else. I thought I was onto the problem when I read about all the transmission electrical coupling issues but that turned out to be for the later 6 speed and mine is the 05 4 speed auto. I will look at the fuses next as you suggest just to make sure the TCM has power. Where are these fuses located? Any photos or numbers to guide me to the relevant ones?

Thanks for your assistance. I may get another chance to work on the car before the week end but then I am overseas again for 2 weeks so there may be some delay.

Best Regards
Alistair

Nitronol

Hi Nitronol here, looking back at some posts by ABZ Vette who had (hopefully has resolved now) a code U0101 and lost comms with TCM on the dash with intermittant door lock, no speedo and stuck in a gear with a kind of rough idle. Did ABZ Vette ever find the fault? I cannot get to the end of his posts.

ABZ Vette if you're out there can you join this please!

I have exactly the same fault now on my 05 C6, had the car from new, I imported into the UK myself, it has only 32k miles and is in real nice shape.

Apparently there was a TSB this something to do with an electrical connector on or near the trans?

Any offers of help welcome! Please

Antony
Nitronol

SunsetOrange05SS

I am also experiencing these same symptoms and can't seem to track down root cause here. I don't appear to be getting 12V with key on / ignition on to the TCM, I tried to initiate this by jumpering a small wire direct to battery from the correct pin but still doesn't give me any transmission temp reading. Anyone have any ideas here?

Nitronol

Hi SunsetOrange05
No, I have not resolved the issue on my low mileage 05 C6 that showe lost comms with TCM. This is due to my worklooad and not had chance to chase again. Speaking to some in the indutry meanwhile it appears that grounds are of some issue being a composite car. Loss of ground is just as catastophic as loss of power to a unit, like the TCM. I know there was the issue of the steering posision censor which I will check again, otherwise when I get more time I will start chasing grounds especially for the TCM.
If you find anything in the meantime please post. It hurts me to look at this vehicle in dry storage unable to be used currently.
Best
Nitronol