No codes, but no C12 either
Thread Starter
LS/MFT
Joined: Jun 2000
Posts: 5,874
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From: Cary IL
St. Jude Donor '09-'10-'11-'12
No codes, but no C12 either
Have done most of the service manual diagnostic procedures -- need advice from The Experienced.
Details: C68 control was giving me a code 9 (low coolant). Checked the charge -- it's fine. So the SM says to jumper the compressor coolant pressure switch. Compressor does not engage (clutch will operate when I present 12V, so the clutch is good). SM says that this may mean that there is an ECM problem. My Scantool does not show the normal C12 (basic state code) which you would get by jumpering terminal A to B on the ALDC -- only fault codes. (When I do jumper A to B the SES does not flash C12.) I show no codes on the Scantool (cannot read C68 module from serial data.) I jumpered terminal A to G to enter the CCM diagnostic mode and the speedo displays C12, but no other codes, so I know the CCM is working fine. SM says to disconnect plug B from the ECM (ignition off) then turn key to ignition "on" to see if there is an SES light -- there is not. This indicates a possible short or ground to the ECM or a failed MEMCAL. Since I cannot read "no codes" I can't diagnose the problem. I am convinced that my C68 code 9 is the result of the ECM problem, not low R12 or the switch. QUESTION: Better to continue diagnosis (which seems fruitless to me at this point) or take it to a Corvette mech for further diagnosis? Anyone who has been thru this problem before, please chime in.
Details: C68 control was giving me a code 9 (low coolant). Checked the charge -- it's fine. So the SM says to jumper the compressor coolant pressure switch. Compressor does not engage (clutch will operate when I present 12V, so the clutch is good). SM says that this may mean that there is an ECM problem. My Scantool does not show the normal C12 (basic state code) which you would get by jumpering terminal A to B on the ALDC -- only fault codes. (When I do jumper A to B the SES does not flash C12.) I show no codes on the Scantool (cannot read C68 module from serial data.) I jumpered terminal A to G to enter the CCM diagnostic mode and the speedo displays C12, but no other codes, so I know the CCM is working fine. SM says to disconnect plug B from the ECM (ignition off) then turn key to ignition "on" to see if there is an SES light -- there is not. This indicates a possible short or ground to the ECM or a failed MEMCAL. Since I cannot read "no codes" I can't diagnose the problem. I am convinced that my C68 code 9 is the result of the ECM problem, not low R12 or the switch. QUESTION: Better to continue diagnosis (which seems fruitless to me at this point) or take it to a Corvette mech for further diagnosis? Anyone who has been thru this problem before, please chime in.
