Hello, I have searched the threads and can not find anyone with a similar situation. I have a 1994 c4 corvette coupe with a 6-speed transmission. The check engine light is a DTC #24 which is a vehicle speed sensor circuit. I am driving the car around just fine and it is giving me an accurate speed reading. I am trying to figure out what this is because I have a smog test in the next week for California and can not have any check engine lights on. Thank you for all the help.

 

How are you checking codes? Is the speed actually accurate? I don't know that if a '94 PCM was 'tinkered with' and MD8 options were ticked in the 'tinker' if you could maybe end up with the situation you have. Have you added maybe a used PCM from a JY or eBAY? Has it been this way since your purchase OR something that's been a recent happening? What were you doing or what changed when it started > if recent and 'self-inflicted'?

There's no other codes? A DTC24 in a PCM controlled system I believe can be affected by more than just a VSS issue.

Do you have a FSM for your car?

 

Hello, I am checking the codes by putting a paperclip through pins 4 and 12 and reading it off of the dashboard intercom where the speed is displayed. And yes, I have reason to believe the speed is correct, I am using my phone to measure the speed and they are reading the same numbers. I bought the car back in November, it was not running, as the guy who had it passed away 6 years ago and the daughter did not want it anymore. Nothing as far as the transmission or engine was modified from my doing, and I originally had a DTC 26 I believe which was the evap system, but I fixed that because the EGR solenoid was not closing. after I installed it and went to check the engine again to both clear the codes and make sure it is operating properly, but when I went to clear the codes, I noticed a c24 and looked it up and saw that it was for a VSS. I have not added a PCM, I am checking every day online at my pick and pulls and nothing is ever there, but I will continue to search in hopes for one day. The check engine light for this has not been active before, so I am assuming from the past week up until now from when the check engine light for DTC 26 came up, that this came up as well and I didn't notice it because a light was already on. As of now, there are no other codes for this car. And I ordered an FSM on the 11th, before even realizing I have a check engine light for this other problem, just because of how helpful they are, and it will be coming here on the 25th, so I thought to post here beforehand in case anyone had this happen to them and knows the fix. I don't know if I need to just replace the VSS and will do it if I need to, but don't want to replace it and realize it is something else instead as they are $80 and I don't have as much money to play a guess and check game. But if this is the best decision, I can.

 

Additionally, are there any threads that maybe you have seen that have a similar issue? I couldn't find any, but I don't know if I was searching correctly (i believe I was, but I am not as familiar with this site as I would like to be).
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Ok, so I just went out to my car and when I ran the diagnostic, it gave me just an h24 (which means history if I am not mistaken). The c24 has disappeared, however, the check engine light is still on. Everything else has either the c12 saying it is good for module 1 or the --- above it for 4.0, 9.0, and A=h24. Any idea what this is? an ECM is $600 off of eBay and there are no c4 corvettes within a 200-mile range on the pick and pulls.

 

So 'now' the VSS code is only 'HISTORY', you mention you've NOT replaced a PCM etc. so I'd suggest you sort a way to start fresh. You're on the 'left coast' so maybe @Nomake Wan is close enough to make a 'house call'. It sat for 6 years and you've driven how many miles since the purchase in Nov '20?

 

I agree with all the above suggestions. If that's now a history code, it will take several drive cycles to clear the codes. If you want to shorten that, you can clear your codes and see if it comes back. Check the procedures on that here. If that car sat for years, then maybe it momentarily had a bad VSS signal but literally cleared out the cobwebs after you drove it around a bit. One other thought: is there any chance this is actually Code 24 for Module 1 (the CCM) instead of Module 4 (PCM)? If so, that's "Courtesy lamp relay coil shorted to battery or CCM internal open circuit." I just want to make sure that you're getting the code you think you are.

EDIT: I pasted the wrong text for the link above. It should be correct now.