opti-spark?
Drifting
Joined: Nov 2018
Posts: 1,796
Likes: 579
From: Mays Landing, NJ
I will start and let run or drive the car in 15-minute or so integrals as you suggest. I'll do it several times. Also, I've tried my best to jump those cavities, and just can't get it done. I'm thinking it may be easier if I had a solid core wire, which I need to go to town and get. If the car starts and runs well, might I still benefit from checking with that diagnostic plug? Thanks again, Doug K.
Last edited by CorvetteRules; Sep 10, 2025 at 02:14 PM. Reason: Correct pin numbers
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
I posted this over and over, so I thought why not do it again, just maybe someone will get it this time, if you're thinking about buying a C-4 remember the newest one is DA DA 30 years old it's got low miles it's still 30+ years old and the ELE system not that robust ,# 1 if you do not have the knowledge or the skills to be able to work on an old C-4 ( they can get kinda compacted ) if don't have the skills # 2 need to know if of a shop that's within 150 miles that WILL and CAN work on it ,and this is a NEW one NEVER PUT WATER ON AN OLD C-4 motor ,if your answer is no to any #1 or #2 are both don't buy one .. and the water deal ,I gots to think about that one .. Sorry about your problem, welcome to being an owner of an old C-4. Good luck ..
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
I posted this over and over, so I thought why not do it again, just maybe someone will get it this time, if you're thinking about buying a C-4 remember the newest one is DA DA 30 years old it's got low miles it's still 30+ years old and the ELE system not that robust ,# 1 if you do not have the knowledge or the skills to be able to work on an old C-4 ( they can get kinda compacted ) if don't have the skills # 2 need to know if of a shop that's within 150 miles that WILL and CAN work on it ,and this is a NEW one NEVER PUT WATER ON AN OLD C-4 motor ,if your answer is no to any #1 or #2 are both don't buy one .. and the water deal ,I gots to think about that one .. Sorry about your problem, welcome to being an owner of an old C-4. Good luck ..
Melting Slicks
Joined: Nov 2016
Posts: 2,256
Likes: 3,082
From: So Cal
2023 C4 of the Year Finalist - Unmodified
[QUOTE=Dougk56;1609088959]Dave, I got the jumpers installed.
Great.
Can you ascribe any meaning to this? TY, Doug
Here's my interpretation.
You left out the indications of "- - - ". These have significance in that they mean "End Of String". These display at the end of the data for each module, then the little number switches to the next module. If all you see for a module is "- - -", that means "no codes".
When I turn the key to "run", in big letters and numbers, I first got H31 on top, with a small 1 or l an inch or so lower. Then the screen read H33, then H35, then H37,
These are all in Module 1 (the small 1) which is the CCM. One of the many things the CCM does is process the data for the center LCD speedometer display.
H31, H33, H35 and H37 all pertain to the circuits to the LCD. My guess is that someone had the center cluster out of the car for repairs and turned the key ON, which set all those codes. They have nothing to do with the no-start.
and after that a small 4. appeared,
Module 4, the ECM. Engine. Interesting that the no-start did not set any codes. This is encouraging. Something was wet, now it's dry and the engine runs. I think you're home free.
followed by a small 9.
Module 9 Antilock Brakes and Traction Control System
, followed by an A.
Module A Air Bags.
and then a 1.0
When it is finished with the read-out, it stops back at Module 1, waiting for further instructions.
~~~~~~~~~~~~~~~~~~~~~~~~
I'd clear out the Module 1 codes, just in the event that if something goes awry in the future you or whoever is working on the car won't be misled by old codes. Eventually they should clear themselves, I believe after 50 ignition cycles. But now that you have a jumper, I'd do it. You can't make a mistake or screw anything up by pushing the "wrong buttons". Learn to be comfortable with and use of the onboard diagnostics.
NOTE: To clear Module 1: Let the data run until it stops at "1.0". Push TRIP/ODO until "1.7" displays. Press and hold ENG/MET until "- - - " displays.
To verify they are clear, turn the key OFF, then back ON. The display will now be 1. C12.
C12 in Module 1 means "no codes" for the CCM. (This is the only module that displays C12. All others display "- - - " for "no codes".)
You asked about driving the car with the jumper in 4 & 12. I don't think it matters or does anything detrimental, but I don't do it. IIRC the speedo doesn't work because the CCM is in Diagnostic Mode.
As long as it continues to start and run normally I'm pretty confident that you can enjoy your new car. Cheers.
Great.
Can you ascribe any meaning to this? TY, Doug
Here's my interpretation.
You left out the indications of "- - - ". These have significance in that they mean "End Of String". These display at the end of the data for each module, then the little number switches to the next module. If all you see for a module is "- - -", that means "no codes".
When I turn the key to "run", in big letters and numbers, I first got H31 on top, with a small 1 or l an inch or so lower. Then the screen read H33, then H35, then H37,
These are all in Module 1 (the small 1) which is the CCM. One of the many things the CCM does is process the data for the center LCD speedometer display.
H31, H33, H35 and H37 all pertain to the circuits to the LCD. My guess is that someone had the center cluster out of the car for repairs and turned the key ON, which set all those codes. They have nothing to do with the no-start.
and after that a small 4. appeared,
Module 4, the ECM. Engine. Interesting that the no-start did not set any codes. This is encouraging. Something was wet, now it's dry and the engine runs. I think you're home free.
followed by a small 9.
Module 9 Antilock Brakes and Traction Control System
, followed by an A.
Module A Air Bags.
and then a 1.0
When it is finished with the read-out, it stops back at Module 1, waiting for further instructions.
~~~~~~~~~~~~~~~~~~~~~~~~
I'd clear out the Module 1 codes, just in the event that if something goes awry in the future you or whoever is working on the car won't be misled by old codes. Eventually they should clear themselves, I believe after 50 ignition cycles. But now that you have a jumper, I'd do it. You can't make a mistake or screw anything up by pushing the "wrong buttons". Learn to be comfortable with and use of the onboard diagnostics.
NOTE: To clear Module 1: Let the data run until it stops at "1.0". Push TRIP/ODO until "1.7" displays. Press and hold ENG/MET until "- - - " displays.
To verify they are clear, turn the key OFF, then back ON. The display will now be 1. C12.
C12 in Module 1 means "no codes" for the CCM. (This is the only module that displays C12. All others display "- - - " for "no codes".)
You asked about driving the car with the jumper in 4 & 12. I don't think it matters or does anything detrimental, but I don't do it. IIRC the speedo doesn't work because the CCM is in Diagnostic Mode.
As long as it continues to start and run normally I'm pretty confident that you can enjoy your new car. Cheers.
Last edited by IHBD; Sep 10, 2025 at 08:51 PM.
Thread Starter
Instructor
Joined: Aug 2025
Posts: 181
Likes: 21
From: north central Iowa
IHBD, I will tomorrow try to clear out the Module 1 codes. So glad to hear my car nay be ok. Your help has been close to invaluable, and I'll let you know how the clearing goes. I also thought highly of what corvetterules did to make easier access to the plug. I looked online and saw a 1-meter length male to female 16-pin adapter plug for just $6.99. I ordered, so if ever I need to do diagnostics again, it'll be much simpler. I sure have benefitted from all the help. Hope I'm free to contact you again when need arises. Doug K.
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Thread Starter
Instructor
Joined: Aug 2025
Posts: 181
Likes: 21
From: north central Iowa
I posted this over and over, so I thought why not do it again, just maybe someone will get it this time, if you're thinking about buying a C-4 remember the newest one is DA DA 30 years old it's got low miles it's still 30+ years old and the ELE system not that robust ,# 1 if you do not have the knowledge or the skills to be able to work on an old C-4 ( they can get kinda compacted ) if don't have the skills # 2 need to know if of a shop that's within 150 miles that WILL and CAN work on it ,and this is a NEW one NEVER PUT WATER ON AN OLD C-4 motor ,if your answer is no to any #1 or #2 are both don't buy one .. and the water deal ,I gots to think about that one .. Sorry about your problem, welcome to being an owner of an old C-4. Good luck ..
Drifting
Joined: Nov 2018
Posts: 1,796
Likes: 579
From: Mays Landing, NJ
I suggest you get a Factory Service Manuel for your year which provides a lot of diagnostic information. It would really help you in deciding what work you can do and when you'd think a professional should do. Also, YouTube is your friend when it comes to finding videos of repairs you may want to do.
Thread Starter
Instructor
Joined: Aug 2025
Posts: 181
Likes: 21
From: north central Iowa
Ty
Glad that you should now be able to enjoy the car and I'm sure you will. As with any 30 year old car even if regularly serviced things wear out so this won't be the last repair to be made. Just in the last 18 months I've had the brake lines from the ABS module to the wheels replaced because of rusted lines, replaced the fuel pump as preventative maintenance because it started making a grinding/squealing noise, replacing spark plugs, fuel filter and fuel regulator. I can say its worth the effort and costs because it is really enjoyable to cruse around in. Since owning my 95 and previous 91 there have been many things i could do myself. some things I had done by a shop I've used for years for all my cars. I've had no regrets buying either.
I suggest you get a Factory Service Manuel for your year which provides a lot of diagnostic information. It would really help you in deciding what work you can do and when you'd think a professional should do. Also, YouTube is your friend when it comes to finding videos of repairs you may want to do.
I suggest you get a Factory Service Manuel for your year which provides a lot of diagnostic information. It would really help you in deciding what work you can do and when you'd think a professional should do. Also, YouTube is your friend when it comes to finding videos of repairs you may want to do.
Thread Starter
Instructor
Joined: Aug 2025
Posts: 181
Likes: 21
From: north central Iowa
Done
[QUOTE=IHBD;1609090041]
I went out this morning to re-set the codes, and everything went exactly as instructed. I feel so good! I know I say thank you a lot, but only because I do thank you a lot. Take care. Doug K.
Dave, I got the jumpers installed.
Great.
Can you ascribe any meaning to this? TY, Doug
Here's my interpretation.
You left out the indications of "- - - ". These have significance in that they mean "End Of String". These display at the end of the data for each module, then the little number switches to the next module. If all you see for a module is "- - -", that means "no codes".
When I turn the key to "run", in big letters and numbers, I first got H31 on top, with a small 1 or l an inch or so lower. Then the screen read H33, then H35, then H37,
These are all in Module 1 (the small 1) which is the CCM. One of the many things the CCM does is process the data for the center LCD speedometer display.
H31, H33, H35 and H37 all pertain to the circuits to the LCD. My guess is that someone had the center cluster out of the car for repairs and turned the key ON, which set all those codes. They have nothing to do with the no-start.
and after that a small 4. appeared,
Module 4, the ECM. Engine. Interesting that the no-start did not set any codes. This is encouraging. Something was wet, now it's dry and the engine runs. I think you're home free.
followed by a small 9.
Module 9 Antilock Brakes and Traction Control System
, followed by an A.
Module A Air Bags.
and then a 1.0
When it is finished with the read-out, it stops back at Module 1, waiting for further instructions.
~~~~~~~~~~~~~~~~~~~~~~~~
I'd clear out the Module 1 codes, just in the event that if something goes awry in the future you or whoever is working on the car won't be misled by old codes. Eventually they should clear themselves, I believe after 50 ignition cycles. But now that you have a jumper, I'd do it. You can't make a mistake or screw anything up by pushing the "wrong buttons". Learn to be comfortable with and use of the onboard diagnostics.
NOTE: To clear Module 1: Let the data run until it stops at "1.0". Push TRIP/ODO until "1.7" displays. Press and hold ENG/MET until "- - - " displays.
To verify they are clear, turn the key OFF, then back ON. The display will now be 1. C12.
C12 in Module 1 means "no codes" for the CCM. (This is the only module that displays C12. All others display "- - - " for "no codes".)
You asked about driving the car with the jumper in 4 & 12. I don't think it matters or does anything detrimental, but I don't do it. IIRC the speedo doesn't work because the CCM is in Diagnostic Mode.
As long as it continues to start and run normally I'm pretty confident that you can enjoy your new car. Cheers.
Great.
Can you ascribe any meaning to this? TY, Doug
Here's my interpretation.
You left out the indications of "- - - ". These have significance in that they mean "End Of String". These display at the end of the data for each module, then the little number switches to the next module. If all you see for a module is "- - -", that means "no codes".
When I turn the key to "run", in big letters and numbers, I first got H31 on top, with a small 1 or l an inch or so lower. Then the screen read H33, then H35, then H37,
These are all in Module 1 (the small 1) which is the CCM. One of the many things the CCM does is process the data for the center LCD speedometer display.
H31, H33, H35 and H37 all pertain to the circuits to the LCD. My guess is that someone had the center cluster out of the car for repairs and turned the key ON, which set all those codes. They have nothing to do with the no-start.
and after that a small 4. appeared,
Module 4, the ECM. Engine. Interesting that the no-start did not set any codes. This is encouraging. Something was wet, now it's dry and the engine runs. I think you're home free.
followed by a small 9.
Module 9 Antilock Brakes and Traction Control System
, followed by an A.
Module A Air Bags.
and then a 1.0
When it is finished with the read-out, it stops back at Module 1, waiting for further instructions.
~~~~~~~~~~~~~~~~~~~~~~~~
I'd clear out the Module 1 codes, just in the event that if something goes awry in the future you or whoever is working on the car won't be misled by old codes. Eventually they should clear themselves, I believe after 50 ignition cycles. But now that you have a jumper, I'd do it. You can't make a mistake or screw anything up by pushing the "wrong buttons". Learn to be comfortable with and use of the onboard diagnostics.
NOTE: To clear Module 1: Let the data run until it stops at "1.0". Push TRIP/ODO until "1.7" displays. Press and hold ENG/MET until "- - - " displays.
To verify they are clear, turn the key OFF, then back ON. The display will now be 1. C12.
C12 in Module 1 means "no codes" for the CCM. (This is the only module that displays C12. All others display "- - - " for "no codes".)
You asked about driving the car with the jumper in 4 & 12. I don't think it matters or does anything detrimental, but I don't do it. IIRC the speedo doesn't work because the CCM is in Diagnostic Mode.
As long as it continues to start and run normally I'm pretty confident that you can enjoy your new car. Cheers.