. Of course it happened in a random parking lot and not at home 
Broken CCM?
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
Broken CCM?
I have a 91 6spd. I was driving it the other day with the AC on and stalled the engine. After the stall, the AC head unit has gone completely dead (no readout/no green lights but the backlight does work), and the fuel economy read 0 constantly on the dash. I also lost all control of the trip monitor stuff, the buttons to change the information quit working. The dash flashes sys, but the engine runs and drives fine. I also noticed that the radio and lights shut off immediately when you turn off the key, they won't stay on until you open the door.
Today I disconnected the battery, and when I reconnected it, my odometer had reset itself! 0 miles! This has me concerned that my CCM is fried.
Does this mean I need a new CCM, or is there something else I should check first? If I do need a CCM can I get the original mileage programmed back into it?
Thanks
Today I disconnected the battery, and when I reconnected it, my odometer had reset itself! 0 miles! This has me concerned that my CCM is fried.
Does this mean I need a new CCM, or is there something else I should check first? If I do need a CCM can I get the original mileage programmed back into it?
Thanks
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
I let it sit for a minute and turned on the lights, which lit up the dash. It is now again showing the correct mileage and it did start. Other issues are still going though.
I do have an FSM however I am not at home at the moment. I doubt the ECM is not causing an issue because the engine runs normally. I replaced it about a year ago as well. The issue seems to be with the non-engine stuff, interior things. I believe that is controlled by the CCM. I went through the fuses and didn't find anything although I can look again later. Diagnostic mode is not working, so I can't read any codes. I can try plugging into TunerPro but that will have to wait until I get home.
I'm not set on the idea that the CCM needs to be replaced, but I do believe that whatever is going on is related to the CCM.
I do have an FSM however I am not at home at the moment. I doubt the ECM is not causing an issue because the engine runs normally. I replaced it about a year ago as well. The issue seems to be with the non-engine stuff, interior things. I believe that is controlled by the CCM. I went through the fuses and didn't find anything although I can look again later. Diagnostic mode is not working, so I can't read any codes. I can try plugging into TunerPro but that will have to wait until I get home.
I'm not set on the idea that the CCM needs to be replaced, but I do believe that whatever is going on is related to the CCM.
Melting Slicks
Joined: Nov 2016
Posts: 2,219
Likes: 3,046
From: So Cal
2023 C4 of the Year Finalist - Unmodified
The CCM and HVAC are not interconnected, but share a common fuse. "A/C"
The other two fuses for CCM power are CCM and LCD
Your symptoms suggest that the CCM is not fully powering ON. The A/C fuse provides the "hot in run" power to the CCM. Be sure that fuse is good and it is tight and not corroded.
The SYS message indicates there is an active, Current code in the CCM. Even if the buttons don't work, the diagnostics should. Jumper A&G, turn the key to RUN, watch the codes. The first group in Module 1 are the CCM codes. You're interested in any C codes except C12.
And I know that by now you have checked and rechecked both battery cable connections at the battery, right?
The other two fuses for CCM power are CCM and LCD
Your symptoms suggest that the CCM is not fully powering ON. The A/C fuse provides the "hot in run" power to the CCM. Be sure that fuse is good and it is tight and not corroded.
The SYS message indicates there is an active, Current code in the CCM. Even if the buttons don't work, the diagnostics should. Jumper A&G, turn the key to RUN, watch the codes. The first group in Module 1 are the CCM codes. You're interested in any C codes except C12.
And I know that by now you have checked and rechecked both battery cable connections at the battery, right?
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
The CCM and HVAC are not interconnected, but share a common fuse. "A/C"
The other two fuses for CCM power are CCM and LCD
Your symptoms suggest that the CCM is not fully powering ON. The A/C fuse provides the "hot in run" power to the CCM. Be sure that fuse is good and it is tight and not corroded.
The SYS message indicates there is an active, Current code in the CCM. Even if the buttons don't work, the diagnostics should. Jumper A&G, turn the key to RUN, watch the codes. The first group in Module 1 are the CCM codes. You're interested in any C codes except C12.
And I know that by now you have checked and rechecked both battery cable connections at the battery, right?
The other two fuses for CCM power are CCM and LCD
Your symptoms suggest that the CCM is not fully powering ON. The A/C fuse provides the "hot in run" power to the CCM. Be sure that fuse is good and it is tight and not corroded.
The SYS message indicates there is an active, Current code in the CCM. Even if the buttons don't work, the diagnostics should. Jumper A&G, turn the key to RUN, watch the codes. The first group in Module 1 are the CCM codes. You're interested in any C codes except C12.
And I know that by now you have checked and rechecked both battery cable connections at the battery, right?
Melting Slicks
Joined: Nov 2016
Posts: 2,219
Likes: 3,046
From: So Cal
2023 C4 of the Year Finalist - Unmodified
I can't get the codes from the ALDL.
I tried jumping the pins
connecting to TunerPro
A&G are the CCM. A is the ground, top right. G is CCM, bottom left. Use your paper clip and report back.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
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
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
In a 1991 there are 5 pairs of terminals that will "pull codes". A&B, A&C, A&G, A&H, A&K. Depends on which system you want the codes for.
Which pins?
Can Tunerpro read CCM data? I know squat about Tunerpro, but I've seen others (perhaps you?) on here say that Tunerpro turns off the CCM so it can 'see' ECM data.
A&G are the CCM. A is the ground, top right. G is CCM, bottom left. Use your paper clip and report back.
Which pins?
Can Tunerpro read CCM data? I know squat about Tunerpro, but I've seen others (perhaps you?) on here say that Tunerpro turns off the CCM so it can 'see' ECM data.
A&G are the CCM. A is the ground, top right. G is CCM, bottom left. Use your paper clip and report back.
I'll try the fuses, and I'll try to jump the ALDL again. Any other suggestions you may have I will be happy to try as well. I won't be able to until this evening however, and I may wait until tomorrow because its a late night for me tonight with an early morning tomorrow.
Thread Starter
Racer
Joined: Aug 2021
Posts: 409
Likes: 82
From: NW Arkansas
It was the A/C fuse. I feel very silly for having missed that the first time, and for having made a whole post without doing the proper diagnostics first. I did check the fuse, but apparently didn't look at it hard enough. It was kind of hard to tell. I stole the heated mirror fuse and its all working now. Sorry for wasting your time with this issue, I got scared over the odometer resetting itself and wasn't in a place where I could do much. Thanks for all the helpful insight.