CCM Possessed
Thread Starter
Instructor
Joined: Jun 2004
Posts: 247
Likes: 0
From: Derry nh
CCM Possessed
my '91 has an intermittent no-start condition which I think is related to the CCM. When in no-start mode, power and ground pins measure as expected. When car is working normally, ground pins "float" at around 50 Ohms to chassis (not the 2 Ohms that I'd expect)! This is completely backwards from what I'd expect.
I'm really stumped.
I'm really stumped.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 247
Likes: 0
From: Derry nh
Did some thinking... the odd resistance was due to a small voltage drop between chassis and the CCM ground pins. WHen the CCM is working normally, it's drawing some current, and the resistance in the ground lead is developing a small voltage i.e. 15mV, which is messing up the resistance measurement.
THat said, when the CCM is NOT working it's not drawing current and I get stable resistance-to-ground measurements of about an Ohm. Since it appears the CCM is always drawing some current, don't know what causes it to shut down, unless it's supposed to go to sleep and it is when it shouldn't be. Some of the CCM inputs i.e. door switch, headlight switch, are called "wake up" inputs so maybe it's supposed to sleep. Going to try measuring through an open window without waking the CCM up by opening a door and see if it's sleeping.
Anyone out there know what makes a CCM tick?
THat said, when the CCM is NOT working it's not drawing current and I get stable resistance-to-ground measurements of about an Ohm. Since it appears the CCM is always drawing some current, don't know what causes it to shut down, unless it's supposed to go to sleep and it is when it shouldn't be. Some of the CCM inputs i.e. door switch, headlight switch, are called "wake up" inputs so maybe it's supposed to sleep. Going to try measuring through an open window without waking the CCM up by opening a door and see if it's sleeping.
Anyone out there know what makes a CCM tick?
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,008
From: Texas
Extremely rare for a CCM to fail. Intermitent no starts are typically one of the following...
- Worn ignition key (the resistance pellet wears over time)
- Worn contacts in the ignition lock tumbler
- Loose and/or dirty wires at the starter.
My money is on the first one. And yes...the CCM goes to sleep just like you described otherwise it runs the battery down over the course of a few days to a week.
- Worn ignition key (the resistance pellet wears over time)
- Worn contacts in the ignition lock tumbler
- Loose and/or dirty wires at the starter.
My money is on the first one. And yes...the CCM goes to sleep just like you described otherwise it runs the battery down over the course of a few days to a week.
Safety Car
Joined: Oct 2008
Posts: 4,689
Likes: 4
From: Yucaipa CA
you know my 90 has some black box which looks like a vats decoder box mounted under the passenger hush panel. when this thing is unplugged the car will not start.
anybody know what this is? It is mounted to a plastic panel all by itself and doesn't look aftermarket at all.
anybody know what this is? It is mounted to a plastic panel all by itself and doesn't look aftermarket at all.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 247
Likes: 0
From: Derry nh
Not sure what that "black box" is but could be related. The CCM connects to just about everything in the car anyway!
As for the key pellet idea, I have two keys and both exhibit the issue. Since one's a spare, both don't have the same wear. A "no start" for a bad key makes sense but I've got more symptoms than that. Even without key in ignition, interior lights will all go out on their own (well within the timer interval) or not come on when I open a door. Speedo/odo and backlight will go out sometimes. Won't start when either scenario is present.
Appears the CCM is going to sleep when in shouldn't and not waking up when it should. Sounds like a typical teenager!
Going to list all the "wake-up" and "sleep" conditions and try to verify they work correctly. May give me some insight. I can buy a CCM and have it programmed for $250 total but I too have read that its failure is rare so that'll be a last resort.
As for the key pellet idea, I have two keys and both exhibit the issue. Since one's a spare, both don't have the same wear. A "no start" for a bad key makes sense but I've got more symptoms than that. Even without key in ignition, interior lights will all go out on their own (well within the timer interval) or not come on when I open a door. Speedo/odo and backlight will go out sometimes. Won't start when either scenario is present.
Appears the CCM is going to sleep when in shouldn't and not waking up when it should. Sounds like a typical teenager!
Going to list all the "wake-up" and "sleep" conditions and try to verify they work correctly. May give me some insight. I can buy a CCM and have it programmed for $250 total but I too have read that its failure is rare so that'll be a last resort.
Racer
Joined: Jan 2007
Posts: 274
Likes: 0
From: Muskogee OK
you know my 90 has some black box which looks like a vats decoder box mounted under the passenger hush panel. when this thing is unplugged the car will not start.
anybody know what this is? It is mounted to a plastic panel all by itself and doesn't look aftermarket at all.
anybody know what this is? It is mounted to a plastic panel all by itself and doesn't look aftermarket at all.
There should also be a two wire dead end connector hanging out there that comes from the ignition switch. You can use a VOM to check the resistance of the bypass and then check the reading from your key on the connector from the switch to see if they're the same. If you want to take it to a stock configuration, you can troubleshoot from there. Otherwise, don't worry about it, although it will be easier to steal.
Safety Car
Joined: Oct 2008
Posts: 4,689
Likes: 4
From: Yucaipa CA
It sounds like a VATS bypass box if the car won't start. The previous owner probably had probems with the switch or key and took that route to a cure.
There should also be a two wire dead end connector hanging out there that comes from the ignition switch. You can use a VOM to check the resistance of the bypass and then check the reading from your key on the connector from the switch to see if they're the same. If you want to take it to a stock configuration, you can troubleshoot from there. Otherwise, don't worry about it, although it will be easier to steal.
There should also be a two wire dead end connector hanging out there that comes from the ignition switch. You can use a VOM to check the resistance of the bypass and then check the reading from your key on the connector from the switch to see if they're the same. If you want to take it to a stock configuration, you can troubleshoot from there. Otherwise, don't worry about it, although it will be easier to steal.
No it's not that ... It plugs into the dash harness and I see no splicing and how its mounted that appears factory to. I will look at it for numbers when I get a chance.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Safety Car
Joined: Oct 2008
Posts: 4,689
Likes: 4
From: Yucaipa CA
Okay here is the plastic box that if unplugged my car wont turn over or anything. It is mounted to a inner dash panel I think that mounted a set of 3 relays I cant remember. Its definitely a factory thing though and only part numbers on it are AC 25075065 37EB
I believe its just the cruise control module, but why would the car not start with it unplugged?
I believe its just the cruise control module, but why would the car not start with it unplugged?