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I've researched this to death, but so far, no success. I'm locked out of using any of the digital readouts in the speedometer area due to this. My new-to-me 1994 does have an aftermarket head unit, but I have already put the 1k 0.5W resistors in place per the attached TSB. There are no active/stored codes when connecting a paperclip or an OBD1 scanner. I don't have a stock radio to swap in and see if the problem goes away.
Battery appears to be healthy, and the alternator is >14V while running.
What other random fixes have some of you found over the years?
Last edited by scorp508; Jun 24, 2024 at 11:19 AM.
Update, this is now fixed. On an evening drive I noticed my Trip Monitor button backlights were not working. I removed the Trip Monitor and sure enough a 5-pin header connector behind it had become disconnected. I attached it and the SYS is now gone and the cluster is fully functional.
Dead backlighting on the trip monitor gave me a clue.
Header connector had come off behind the trip computer.
Cluster back to 100% operational.
Last edited by scorp508; Jun 24, 2024 at 11:18 AM.
Reason: Add photos.
There was a thread awhile back where dizwiz chased a SYS message for weeks. Same "no codes" response. He was finally persuaded to jumper the CCM diagnostic pins (A&G or 4&12) and report all the codes displayed. One of them was Module 1 (the CCM) C15. A Current 15 is an open circuit in the buttons. He found exactly what you did, the connector for the buttons was disconnected.
A SYS message means there is an active code in the CCM which in your case would be C15. C codes are always accompanied by the associated History code. You probably still have an H15 in Module 1 if you haven't cleared the CCM codes. No issues by leaving the H15 there, but if you're curious, jumper 4&12 and turn the key to RUN. Now that the buttons work, you can clear the H codes using the buttons.
Thanks for the follow up and posting the solution.
There was a thread awhile back where dizwiz chased a SYS message for weeks. Same "no codes" response. He was finally persuaded to jumper the CCM diagnostic pins (A&G or 4&12) and report all the codes displayed. One of them was Module 1 (the CCM) C15. A Current 15 is an open circuit in the buttons. He found exactly what you did, the connector for the buttons was disconnected.
A SYS message means there is an active code in the CCM which in your case would be C15. C codes are always accompanied by the associated History code. You probably still have an H15 in Module 1 if you haven't cleared the CCM codes. No issues by leaving the H15 there, but if you're curious, jumper 4&12 and turn the key to RUN. Now that the buttons work, you can clear the H codes using the buttons.
Thanks for the follow up and posting the solution.
I learned a couple things today, one being my OBD1 scanner apparently doesn't show CCM codes.
With the paperclip I get the following. I've jotted them down and cleared everything via the buttons now that they work as I don't know which pre-existed my ownership. If stuff comes back I'll dig into it. For what it is worth this is a ZR-1, so the codes may not align to the LT1 cars.
Mode 1 (CCM):
H13: DIC Switches Open or Shorted to B+
H41: Loss of PCM/ECM Serial Data Communications
Mode 4 (PCM/ECM):
H33:
H46
Mode 9 (ABS/ASR):
H72
Mode A (DERM):
Nothing.
Last edited by scorp508; Jun 24, 2024 at 02:18 PM.
"SYS" flashing on 1994, but no codes.
