Corvette CCM Reverse Engineering Anyone?

[NomakeWan]

I've got a bizarre one for you.

So the past month I've been away from home due to family emergencies across the US. I've barely had any time to be with the car, so it just sat in the driveway. Well, after having sat for only a few weeks, I went to open it and nothing happened. Figured my keyfob was dead and unlocked it manually, but noticed the interior lights didn't come on either. Didn't have time to deal with it before hopping a plane so I used another car instead.

When I finally got back a few days ago, I checked the battery and it had 1.2V. Not a typo. Had bought the battery brand new back in May, but figured okay, maybe defective. The '90 has been sitting in our garage for even longer and it still reads 10.6V (before I put the tender back on it). So I got the battery replaced under warranty, tossed it on the car, and that brought everything back.

Except that now my odometer reads 0.

How in the actual fuck? Isn't the CCM's userspace NVRAM? It's not supposed to care if there's no voltage, right? Why would a near-dead battery cause the CCM to reset? Has anyone even heard of this? Anybody know why?

I have a dump from the '95 I took before, and I have a photo on my phone showing I hit 129,000 miles on September 17th of this year, so I won't be up shit creek reflashing it. But I'm just...flabbergasted.

[steveo]

it's definitely not supposed to do that - however if it is truly at zero miles i think you should be able to reprogram it in-car without using the 'reman pin'. i think it'd be more likely that it's a communication issue between the dash and ccm or something

[NomakeWan]

I haven't tried plugging in and asking it for a Mode 5 yet. I plan on doing that next. It started raining only a few minutes after I managed to get the battery in (which was why I was in such a hurry to do that).

But I flicked through all the dash controls to be sure--they all function correctly. Trip and Odo both read 0 (trip reading 0.0). It most certainly looks like the EEPROM has been blanked somehow.

As soon as I have an opportunity I will update with more information. I've never seen this before.

EDIT: Went back out to the car, turned the key, and the odometer was back. Confirmed with Flashhack that it's locked.

I wonder if this is a vulnerability? A code path that was not accounted for?

Basically the CCM lived with less than 5V going to its power pins for almost a month. Then I took that battery out, slapped a fresh one in, and the first thing I did was unlock the car with the keyfob, then turn on the parking lights to engage the digital dash. That's when it read 0. Had it not been starting to rain I would've run in and grabbed my laptop. But it appears that this first powerup might be going down the wrong code path for some reason.

It's all good now though--confirmed by reading it with Flashhack and by using my Tech 2 that everything's the same as it was before.

[steveo]

solar flare ?

[NomakeWan]

Hilariously during one of my team's races we did actually get affected by space weather--it made the datalogging we did pretty much unusable becaus the GPS coords were unreliable (the datalogger actually thought we were on the track next to the track we were on at one point).

But I don't believe there has been any significant solar activity within the past few hours.

[spfautsch]

This one is really baffling. When I get done with my current basement junk purge I'll pull the test setup down and see if I can reproduce (though I lack an instrument panel).

If I can and it does enable the mode 5 check the "hotwire" wouldn't be needed.

I'm leaning towards steveo's initial theory of a problem with the comms to the lcd.

BTW, the trip odometer in these is stored in ram so a power loss wipes it along with all fuel consumption data.

Touching wood, mine has been living the storage unit lifestyle for going on a year and hasn't drained the battery yet. I check it whenever I go to the unit, and will drive it to work when it gets down to 12.0v.

[NomakeWan]

Yeah, the trip going to 0.0 was totally expected. That's why I thought initially that I had somehow gotten into trip mode instead. Only to flip over and realize no, that was the normal odometer reading "0" with no decimals, and no trip. Every other gauge on the dash worked fine.

Trust me, I was totally shocked. And I'm absolutely kicking myself for not grabbing my laptop and plugging in right then and there. While I'm glad that my CCM isn't magically corrupted, I'm also irritated that I didn't confirm Mode 5 while the dash was reading 0 miles...