So - My 2012 GS Auto is continuing to drive me Absolutely Crazy !!!

Several months ago - I posted about a long delay between pushing the start button and the engine cranking and The "Service Traction Control" & Service Active Handling System" messages on the DTC, along with it being locked in 4th gear.

https://www.corvetteforum.com/forums...endations.html

I removed the battery and went after grounds - and things temporarily improved - but then reverted. I was getting a U0100 (Communication Error) & P0700 (Trans Control Module) codes.

I recently brought the car to an Independent shop I have used in the past, and have some faith in (the fact that the owner/mechanic has a CTS-V that will run in the 9's may have influenced my decsiion - although he specializes in German vehicles). We hooked up his pro level scanner, and I saw codes that I did not see on my Tech II (clone).

We then spent some time pulling darn near every major (EFI related) electrical connector on the car (except the BCM connectors) - and spraying them with contact cleaner. The only thing we found corrosion on was a connector near the battery. That connector only had one wire in it - but it was a fairly beefy connector (the shell was green) with a pretty serious spade lug inside. We cleaned that decently - and then moved to the underhood fuse block and removed and re-seated every single relay in the box. The car started right up and ran fine. Thinking the problem was resolved - I headed home - maybe 20 minutes of run time later - the speedo started jumping, and the "Service Traction Control" & "Service Active Handling System" messages reappeared - along with the check engine light. The car was still shifting - but one time it shifted VERY hard at light throttle. I got it home - and pulled the codes I got a U2108 (Lost Communication with the ABS / TCM module) & a C0561 (appears to be a companion code to the 2108).

I pulled the three main connectors at the BCM, sprayed them with contact cleaner- and reinstalled them, then cleared the codes. I started the car - and things seemed fine - so I took the car for a ride and after maybe another 20 minutes of run time (maybe 5 miles of driving) the speedo again started dropping, and the ""Service Traction Control" & "Service Active Handling System" messages reappeared.
I just pulled the codes, and got PO700 (TCM), U2108 (Lost Communication with EBCM), U2106 (lost Communication with Trans Control System) , U2105 (some type of CANBUS error), U0100 (Lost Communication w ECM / PCM), U0140 (Lost communication with BCM), U0101 (Lost Communication with TCM). I went to the Chassis Control portion of the Tech II menu, and it appears that the Tech II was able to communicate with each of these modules.

So - If you were in my Shoes - Where would you go from Here ???

(I should mention the PCM was replaced about a year ago - P0601 - Memory Checksum error - and while it was a new PCM - it was programmed by a 3rd party - not a GM dealer. Think I should try changing the PCM ???)

 

Some thoughts:

Clean the BCM connectors. They're easy to get to and frequently get dirty.

With the car off, measure the resistance across pin 6 and pin 14 of the OBD2 port. It should be 60 ohms.

Triple-check battery voltage. Is it going low under some condition? If your multimeter has MIN/MAX feature, you can leave it on as you drive.

The BCM harness emerges from the firewall into the engine compartment beside the battery. Does the outer jacket look okay? It can get covered in white crusty battery chemicals over the years that do a number on the conductors inside.

 

I don't see anywhere you mentioning the TCM connector into the transmission. That would definitely be something to try as it can cause problems, especially since one of the codes being reported is for the TCM. I once melted one of the wires in the TCM harness and it was causing ALL kinds of problems. I'd remove the connector, make sure none of the pins are bent or damaged and then look to see if any of the wires may have come in contact with the exhaust.

Also, TCM codes never get reported without there being at least 2. It's always a P0700 (indicating a generic transmission problem) followed by a more specific TCM code so you might want to look into that as well to make sure you haven't missed any codes that may give you a better idea of the underlying issue.

 

A mechanic whose car runs in the 9’s a good diagnostician do not make !!…LOL !!…I remember you said you live in Northern NJ….I highly recommend Joes Auto Electric in Bayonne if you would rather take it somewhere !!

 

I agree - my car runs 9s and I don't know squat!

 

lol !!

 

I did pull the 3 connectors off the BCM, and sprayed both sides with contact cleaner ... "I pulled the three main connectors off the BCM, sprayed them with contact cleaner- and reinstalled them, then cleared the codes." The mechanic I was working with also pulled the connector on the TCM, but due to how hard it was to get to - he did not spray it with cleaner - I will plan to do that... I'll also check the condition of the BCM wiring as it comes through the firewall.

Do you think there is something significant about the car running for ~20 minutes / 5 miles or so - then the Service Active Handling / Service Traction Control message coming on ???

I'm also kind of wondering if something is heating up - and that is causing the problem. In the CANBUS system - is one of the modules the "Controller" that the other modules communicate with ???

As for voltage - I'm seeing about 12.3 Volts on the battery with the car off, and about 14.0V with the car running. I have not noticed any instances of voltage drops or spikes - I have my radar detector displaying voltage - and I do see a 0.1V fluctuation farily often, but that's no different from any other car I own, but I'll see if I can find a voltmeter that has a peak hold function.

when I pulled the codes - I only got the P0700 code from the Trans (nothing else) - the Tech II showed "TCM Requested MIL Illumination".

.
And Yes - I get that owning / driving a 9 sec car does not make a someone a good diagnostician - but he does his own work, and is at least somewhat familiar with LS motors / architecture.

Finally - THANK YOU torquetube, subfloor@century trans & C5 Diag... I appreciate the input more than I can express.

 

If it's a slightly burnt wire, that might explain why it doesn't come on immediately as all it takes is for it to slightly move around a bit and trigger a code, whether from driving or just at idle.

In my case the problem in the harness was about 12-15 inches from the TCM connector. It was actually partially obscured by the plastic loom so you might want to pull that back to properly inspect the wiring inside. It may not solve the problem but it never hurts to be thorough.

That voltage sounds right as it always shows more when the car is running.

 

No. All the modules ("nodes") broadcast on the same pair of wires. The good news is that the C6 is pretty simple. There are only six or so nodes on the network. They include the ECM, BCM, EBCM, and TCM.

Most of the other modules you're seeing on your Tech 2 are on a separate bus called the Class 2 Serial bus. Things like the radio, door locks, HUD, HVAC, etc. The BCM acts as a bridge between the CANBUS and the Class 2 Serial bus.

The CANBUS has a terminating resistor at either end. One terminator is in the ECM and the other is in the BCM. If the wiring is intact and everything is plugged in and working, you should see 60 ohms resistance between the two CANBUS wires. This is an easy first test of the physical wiring before you get into more complicated diagnostics.

 

I will check that tomorrow.

 

Here is a drawing that I found on a post about the High Speed CAN bus. It's for a 2008 but should be helpful.

Here is the same diagram from AllDatadiy.

 

Hummm -- Connector in pass side trunk "cubby" - didn't know about that one . I'll put that on the list for a disconnect / spray w Contact Cleaner - and reconnect.

THANK YOU for the diagram,,,

 

So - went out and measured resistance between pics 6 & 14 on the OBDII connector. With my handy dandy $15 Craftsman digital meter - it read 62.3 ohms. I'd call that close enough to the 60 ohm value (and I measured with an extension cable so I didn't have to hang out upside down under the dash.)

Below is a pic I took of the wiring right near the battery. It looks pretty darn good to me...

Thoughts ???



Pic of wiring near battery.

 

In order to see what is going on the High Speed CANBUS, you need to have an oscilloscope or a sophisticated scan tool with an o-scope function. Ideally you want to see two square wave signals that are opposite of each other. As one square wave is in a positive direction, the lower signal square wave goes in a negative direction. Plenty of YT videos on the subject.

The VICM is also the OnStar module.

 

You probably have to remove the battery to see the big cable I mentioned. It comes up from the BCM pass-through behind the battery and goes to the fusebox. All that white crud lands on it.

Your resistance measurement suggests you don't have an open circuit on the CANBUS, or if you do, it's intermittent. You can also check for a short to ground by checking the resistance between either pin and ground, though I don't know what's normal for a C6. Should be in the kohms.

The idea here is to find an obvious fault in the network wiring, if there is one. Otherwise you're going to have to examine the bus with a scope as has been suggested.

 

Purple92. Did you go to the delta station in verona? Just asking because he runs a cts that has a big nasty cam. Never saw it go but it does sound good.

 

The guy I'm working with runs a small 2 bay shop in NW NJ, and there is a Delta gas pump in front of the shop - but he are not in any way affiliated with the Delta. But the shop is NOT in Verona.

The mechanic's CTS-V does have a cam in it, and it's pretty obvious to anyone who knows anything about HP engines.

 

Ah ok. This is a delta also which also has two bays. Not sure if the mechanic is affiliated with delta that pumps gas out front. But his cts is badass. Also has a manual in it as I heard him take off from a light and go through the gears.

 

So - an update for anyone interested.

I spent some more time with my friendly mechanic today. The car was back to doing the serious delay between hitting the start button and the started doing anything (like 10 sec). And the Service Traction Control and Service Active Handling were showing on the DTC by the time I left my driveway to head to the garage. We pulled the trans connector and it looked beautiful - but it got a good hit of spray on contact cleaner before being reassembled. Same thing with the ABS connector..

And just for yucks - I changed out the PCM. I bought a used PCM off E-Bay - and got it programmed to my VIN by the seller. (i would like to have a short "discussion" with the GM engineer who decided how to mount the PCM in the upper pass side fender...) Anyway - after that - I hit the start button, the car lit right up, and ran fine. I ran it for about 10 min,and all seems fine. On my way home - the speedo decided to stop working, but other than that the car seems to be running fine now. I will try driving it around a bit more - and see if any codes for something that could be related to the speedo show, but at least for the moment - the car seems to be doing OK.

Any thoughts ???

 

Just chiming in to see what is the update regarding your issues. I've been doing searches as to how the BCM and ECM communicate during the start mode in an effort to diagnose a problem with my 07. My car too, sometimes has a long delay between powering up (when I push Start) and actually commanding the starter to engage. On some other occasions the car will start up correctly, but won't keep running. Scanning with my HP Tuner I can see that the throttle is not activating although I can see my throttle pedal is sending the command. These problems are intermittent so a bit difficult to diagnose. If I had information as to how the BCM correlates and communicates with the ECM, it would be very helpful. How is your car doing since replacing the ECM?