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Thanks for the answer to my last question. You were right

on! Now, for the next...
Thanks for the answer to my last question. You were right on! Now, for the next problem. I am trouble with the C25 and C72 error. Plus my cruise control has quit. I have checked all relays and fuses.
C25 - when either door is open the error goes to H25, but when all doors are closed the C25 returns.
C72 - I have put in the 1k 1/2 w resistor that should handle the LCD dimmer problem (I have an after market stereo), and the C72 goes away. But after 2-3 days it returns.
Cruise Control - all of a sudden it stopped.
I am asking if you think the problem could be the CCM? I have read of others having problems with the CCM, but would like an experts advice before I try to take it out and have it refurbished.
Thanks for listening.
Jim
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Answered in 1 hour by:
9/12/2017
Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4,831
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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C72: anything that will disrupt the serial data link (ckt 800) will cause this code to set. Certainly, if there is no outward cause for it, a likely culprit is the CCM. Generally, this code sets with no rhyme or reason, and your experience seems to match this. If you don't have a reasonable suspicion that there is something tapped into ckt 800 or anything like that (probably not, or it wouldn't be so intermittent), I would say you're facing CCM replacment.

C25/H25: This indicates a problem with the LF wheel speed sensor. Since the wheel speed sensor is an input to the ASM, it has the ability to disable cruise control. I do not know what doors opened/closed might have to do with this, that is a very odd symptom. This is an ABS trouble code you're retrieving, yes?

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Customer reply replied 2 months ago
Thanks for answering so quick. The C25 error, according to the FSM, says it has to do with the courtesy lights. I tried replacing the relay(twice) and no change.
Thanks again.

That's why I asked which system on the car was giving you this trouble code, it can point to a couple of different things depending on which computer is reporting it.

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Customer reply replied 2 months ago
Oh, got it. The 25 and 72 codes come on when checking module 1. I have no errors in module 4 and 9.
Customer reply replied 2 months ago
Jerry, did you get my response about the error codes? Before I give you an excellent review, please check my response. If you did not get it, I replied:
When I run the diagnostics, I get a 25 and 72 error code for system 1, no errors for system 4, Err code for system 7 and no errors for system 9.
If you need more info, please let me know.
Thanks, Jim

Ah, I am with you now. Sorry for the delay, I've been extraordinarily busy at my regular job and couldn't come back to this until now.

Code 25 in the CCM is an open or short in the interior light relay circuit. Typically, what this means is either a relay with a bad coil (swap the interior lamp relay and retest), or a bad CCM.

Code 72 in the CCM is LCD dimming output circuit short to ground. Again, the CCM is seeing an incorrect voltage on the dimming circuit, which can happen for a variety of reasons, but if the dimming circuits work, I would ignore it. Is it giving you a message or other indication that there is a problem, yet the dimming circuits work normally?

Neither of these is relative to the cruise control, that's something that will need to be treated separately.

Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4,831
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
Verified
Jerry Newton and 87 other Chevy Specialists are ready to help you
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Customer reply replied 2 months ago
I understand about the delay.
Code 25 - I tried swapping the relay with another, and a new relay, but no change. I think you are right about the CCM.
Code 72 - My problem is that it is an aftermarket radio, and the installer (prior owner) did not connect the dimming wire to anything. According to another customer of JustAnswer, I tried installing a resistor in line. It worked for awhile, then the error returned. I installed another resistor and the same thing happened. Could this be another CCM problem? I found a Corvette shop that does CCM refurbishing, for $270. Think this is a good price?
Thanks for all your help.
Customer reply replied 2 months ago
Hi Jerry,
I will of course give you a high rating for your help. I just found out something that may help. When you close a door the courtesy lights are suppose to stay on and dim down. But on mine, the lights go off immediately. Any help?

The CCM controls this dimming as well. I think you are headed for CCM replacement on this.

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Customer reply replied 2 months ago
Thanks for all your help. I will remove the ccm and have it refurbished.
Jim
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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4,831
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