I've had an intermittent issue that I've been trying to assess this year at the track, and I could use some advice related to hunting it down.
The vehicle is an early 2015 C7 Z51 M7.

After almost exactly 11 minutes of track driving in 95+ Fahrenheit weather, the instrument cluster will lose all telemetry, and warnings to service power steering, stabilitrack, etc will appear. Power steering becomes nonfunctional. Power doors become nonfunctional. Other systems may also be unavailable, but it's hard to say because I immediately slow and pit.

The engine retains normal operation and rev-matching continues to work. Even the PDR continues to function without so much as a hiccup in the video playback. No CEL is thrown and no pending codes are found with my obd2 scanner. Oil, coolant, and transmission temperatures appear to be within acceptable levels when this occurs (I have installed the z06 secondary radiator).

Sometimes the system recovers on the drive to my paddock space, but usually I have to turn the vehicle off and back on again. After this, all systems return to normal.

I discovered that the metal finned control modules under the carpet of the hatch area were extremely hot, so I propped up the covering to allow some air in, during morning prep. I got two good sessions in, but the problem returned, probably due to ambient temperatures rising after noon.

Before my final session of the weekend, I remembered this post (https://www.corvetteforum.com/forums...air-scoop.html) and quickly replicated that solution. I had a problem-free session then, but one data point is a little skimpy.

Any advice for hunting this issue down? Is it possible this is all just related to the power steering motor overheating? Any other thoughts or observations?

 

Bump for anyone with some troubleshooting tips for the above. Worth it take to a dealer to see if their scanners can find something an off-the-shelf obd2 scanner can't?

 

GM did release a TSB for the overheating power steering. I only heard the PS failed not a lot of other things. I installed the GM recommended parts before I ever took my Z06 to the track. I have a scoop made from a C6 Z rear brake duct sticking out of the bottom of the car that directs air right onto the PS motor. Have been tracking the car since April 2016 without having an issue with the PS motor.

I am attaching a copy of TSB PI1535A which describes how to make the cooling duct.

Bill

 

This is a long-shot based on something similar I saw in a race car quit some time ago. I'd suggest replacing every fuse and plug-in relay that I could. I'd say any that may be involved with powering the affected functions, but I don't know if there is a single one, or... The reason I say this (and it might do zilch) was a fuse that looked good and even tested good until it reached a certain temp and then it was intermittent. Drove us nuts for a while until I said, "What have we got to loose?"

One other intermittent cause I've seen was a faulty molded metal end on a battery cable that attached to the battery. Again, it would wiggle or heat up just wrong and malfunction, though was fully undetectable otherwise. When I found it and cut the molded end apart, though it looked perfect from the outside, the copper cable was loose, black, and heavily corroded on the inside. All the best, in any event!!!

 

First, thank you both for the advice! Additionally I talked directly with a forum member more active in the C6 section, who also seemed to think this was not a failing module, but a CAN bus issue. He pointed me towards a better scanner capable of running more detailed diagnostics.

Having ran the diagnostics now, every single module has a stored history dtc (but no current dtc) for some kind high speed can bus failure. The most common code was "Control Module Communication High Speed CAN Bus Off", usually paired with specific codes for whichever of its peers it specifically could not reach.

Since this does seem like an overall power issue, I went ahead and re-tightened the battery terminals and connectors and inspected them. I discovered that the battery was not fully secured and could possibly shift around during high-g moments. I doubt this is the root cause, since this issue occurred with the old battery as well, but I've corrected the fitment and will have to wait and see.

Otherwise, I'll be going through the fuse boxes and connectors and doing some visual inspections. I might have to schedule another track day so I can try to catch it in the act.

 

Welp, I thought I had this one taken care of after some clean track days, but I had it happen again today after 22 minutes of really hard driving at Road Atlanta. Full can bus failure that self recovered by the time I got back to the paddock.

Limited myself from there on to 12 minutes on track, a few minutes off to cool.

This is doable but I sure wish I could figure out a mod or repair to negate the need for cool downs.

 

I know it is a bit of a pain but how about removing the trunk carpet completely for your track days?.Having those ecus out in the open should help keep them cool.

 

I actually did something similar to this for the rest of the day. I used the foam battery cover to keep the carpet propped up off the hatch electronics cluster after removing the plastic cover tray. No idea if it helps, but I'll try it again from the start, next event. Perhaps I could even try to find a small fan to plug in to the power socket nearby. At the very least, it would let me mostly eliminate one possible cause before I start down a wire checking nightmare.

 

Get the car on a lift and check the exhaust where the pipes go over the rear axle. Make sure you don't have a leak and that all insulation is in place. Basically, the only thing separating the exhaust from the rear electrical center is a thin piece of SMC/sheet metal.

I know that I used to burn the bottom of my rear carpet on my C5s and C6Z when tracking them.

Bill

 

A quick search for a '12 volt fan' turned up this fan. Already has a plug on the wire. There are a bunch of others in different styles.
Over the years I have seen many threads that problems turned out to be caused by overheated electronics so I suspect you are on to the cause. Good luck.

 

Back again from the track. Today I ran with no rear carpet to attempt to rule out overheating of the modules in the hatch.
First session was okay, but as the day got hotter, the issue returned and got worse.
My last run before I called it a day, I got ~7 minutes before all the gauges lost data and the vehicle went in to limp mode.
I really wish this would throw a CEL so I could at least have something to go on. As it is, I'm still not sure if it's a module overheating or wiring overheating or what. Super frustrating to troubleshoot when everything's fine after a restart.

For now, I guess I'll throw it back on the quickjack and look around. I'm getting closer to throwing in the towel and trying to find a reputable specialist near upstate SC. Anyone have a shop or someone I can contact that they can recommend?

 

The MIL (a check engine light) will not illuminate for the issue you are experiencing…it only illuminates for emission related DTC’s…a scanner that can read the data from all the modules will help…you’ll need to find a shop experienced in scope diagnostics (not dealerships since they don’t use them)…find yourself a diagnostic shop that can hook their scope up to the car while driving and see what is happening when the car heats up…they will scope the CAN bus wiring…a scope is my best friend when it comes to diagnostics !!

 

C5 may be onto something. It's been 10 yrs since I retired from being a Lexus tech but we were using a Toughbook supplied by Lexus for our scan tool. We could easily carry it in the car w/ us and it had a feature where when the problem occurred we just hit a button. That gave us the full data for 30 seconds before we hit the button to 30 seconds after. When we were looking at the engine control system there was over 100 lines of data. I can't specifically remember what temps were displayed but I know there were a few.

 

Thanks but I’m referring to a labscope and not a higher end scan tool…labscopes have been around for decades…those using them today are few and far between. I can record data PIDS with my scan tool but that does not come close to a labscope…did you use a labscope in your dealership ??…the Picoscope is my weapon of choice !!

 

Thanks for the replies. Buried in my earlier posts, I did pick up a full scan tool awhile ago.

"... every single module has a stored history dtc (but no current dtc) for some kind high speed can bus failure. The most common code was "Control Module Communication High Speed CAN Bus Off", usually paired with specific codes for whichever of its peers it specifically could not reach."

I'm going to reseat connectors and visually inspect as much as I can. I just wish I had some kind of direction for a specific place to focus on.

 

A buddy rented a local .5 mile oval track, so I got to test out the new heat shielding. The track temps were over 100F, so it was an ideal stress test.

No luck. After some warm up laps and tire pressure adjustments, I only got 5 minutes of hard driving before the symptoms reoccurred. Same "High Speed CAN Bus Off" errors as before and back to normal after cooling off.

I guess it's time to find a specialist nearby or arrange to have the car shipped off to one. Any recommendations, especially near-ish to South Carolina would be greatly appreciated.

 

You’re going to have to get this failure while a technician is working in the car or they won’t find anything. I agree the exhaust heat may be a factor in heating a module through the trunk floor. None of the modules in that area get hot to the touch. I would focus on why that is happening.

 

I put the vehicle on a quickjack and did a thorough inspection of the exhaust, even using a borescope to check above the pipes. I found no signs of exhaust leakage, and everything appeared to be in order.

I went after some low-hanging fruit and replaced the alternator and the logistics and ecu relays. Next, I physically lifted the rear fuse box and control units and secured them to a piece of wood so they would not touch the hot floor.

I went to Road Atlanta for another shakedown. Two morning sessions were overcast and cool, with slight sprinkling, and the car performed great. After lunch, the sun came out and temperatures began to rise, and the electrical gremlins reappeared after ~15 minutes of hard driving.

This time, the speedometer started to fluctuate wildly, which I had never seen before. I slowed and prepared to pit, but before I could, the usual "service rear axle/stabilitrack/suspension/etc" messages popped up and the car went back in to limp mode.

Back at the pits, I confirmed that the rear hatch electronics were cool to the touch, but the car did not immediately recover with a power cycle. In fact, the speedometer and transmission gear indicator remained nonfunctional. There was a dash light and my vxdiag scanner was not able to communicate with the diff control module or transmission module. Over the next 20 minutes, the speedometer and then the transmission indicator returned, but curiously the fuel gauge was no longer working. I disconnected and reconnected the battery and the fuel gauge returned.

The car is now back to normal and works just fine with no codes during daily and extended driving.

I'm becoming pretty frustrated at this point and am considering selling the vehicle. I really would rather fix the issue, even if it costs some money, but I hate playing parts darts. I called two shops, including one that specializes in corvettes, and talked extensively with some very helpful mechanics. Unfortunately, neither of them were really sure about what the issue could be, just that "something" is getting hot and maybe a connector or solder joint are the culprit "somewhere".

Any last advice before I throw in the towel? Would a dealership maybe have someone with the know how to troubleshoot this issue?

Thanks to everyone that's chimed in along the way here- even if it doesn't work out, I've appreciated the support.

 

A Dealership would be the LAST place I’d take the car for a diagnosis…where are you located ??….if you’re in Atlanta I’d try Wrights Car Care…they are an auto electric shop…I’d find an auto-electric repair shop…a diagnostic or auto electric shop has

the right equipment to diagnose CAN bus issues…a CAN break out box (BOB) and a labscope…that’s all they need to diagnose this…CAN bus signals are very fast and require a scope since you are measuring it in MICRO seconds (millionth of a second)…this is what you would see on a good CAN bus.

 

I have the Panasonic Toughbook with Techstream for Toyotas and Lexus…great scan tool to have…factory scan tools are the best to use.