Hello, folks. New to forum and just purchased a 95 base model last week. Dealership showed me a check engine light that came on the day of purchase. Auto hauler was already scheduled to pick up that morning. Their dealership technicians told the salesman it was a bad O2 sensor. They sent me two O2 sensors since they didn’t know which one it could be. I got the car here and replaced both sensors. Of course, the check engine light will not go off. In the early stages of repairs, once I got it here, we used a computer for codes that is similar to what the dealerships use. My buddy has one and works for local Chevy house. The code was “coolant temperature signal low voltage or shorted”, so we replaced both temp sensors. Light is still on and will not go off. Finally, we tried the paperclip jump on the OBD2 port and got a code of H47. Tried to clear codes and the H47 will not clear. From what I have read, this is a code in the history. I found something referencing that the 47 code was the knock sensor. Replaced both of those. Still has the check engine light. H47 code is still there in the 4.0 area of the computer scan in OBD2 port. Can someone please help me get rid of this check engine light?? Any ideas? Thank y’all very much from a frustrated new owner.

 

I have a 91( obd1)
useing the paper clip
h stands for history
C for current
You probably have pulled negative bat all ready ?
their is a way to clear code with the paper clip in
think the last menu when switching with the climate trip buttons can't remember without looking
It's probably different in your year anyway.
Someone else on here probably knows more than me ( I was very surprised when the one menu made my horn go off, checking relays ) I kinda just push buttons till something happens probably not the best idea, lol

 

Yes sir! We pulled cable off of battery and tried to clear all of the codes with trip and odometer buttons numerous times. All codes are clear except the H47. Thank you for the reply, sir.

 

Check your PCM and see if the Knock Module is actually there. I would think if missing it would be a 'C' for current but maybe not. I've no LT1 experience.

Do you have the FSM(Factory/Field Service Manual)?

 

I will check that sir. That was our next step is checking that computer and module. It’s all that is left. Thank you sir!

 

Did you make a note of all the codes when you started? It's possible that some that you removed are related to the H47 that you still see. You seem to have spent $$$ on components that weren't necessary. Could someone have messed up a 'tune' of the PCM? Possible I'd think.

 

Hello sir. Thank you for the information. The only two codes that we originally got on the first check on OBD2 was the H47 and an H72. H72 was something with the speedometer I believe. That one was cleared and is gone but the H47 remains and cannot be removed for some reason. And I do believe we did replace some unnecessary parts, especially since the check engine light is still on. I’m going to check into the computer probably tomorrow. Had to work all weekend. If the “tune” you are referring to is the problem, how do you correct it ? New computer?? Thanks again

Brad

 

I'd see if there's a label on the PCM, make note of that number. Remove the cover, look for the Knock Module actually being there and get the number off of it if you can. I believe it should be visible. Your friend that works at the dealer has availability of their scanners? If he does and dependent upon what their using he should be able to scan and verify things. A '95 requires various adapters/connections to use most dealer scanners these days. What brand did he use that gave you the coolant sensor codes?

 

We will try that sir. I am not sure what brand his scanner was but it was a big red one. He said it was about $3000 when he purchased it.

 

Update: Checked the ECM that is on the car. Flipped it over and removed metal plate to discover that the knock sensor module is missing. I am not sure if prior owner replaced the ECM and wasn’t aware that you have to have a knock sensor module or what. Any ideas on how to match a knock sensor module to the ECM on this car? I am assuming it goes by one of the characters in the VIN or something?

 

They're available but are ridiculously priced. I would post a WTB here on the forum and assume someone will give you a reasonable buy on one.

Maybe shop 'local' JY for maybe one.

*** You bought from a dealer? Did they do the PCM and not know any better? Check with them, maybe the core is still around?

*** GM SPO Part numbering hints it needs to be '94 or '95 and 'Vette only. I don't know that to be a fact. Maybe someone does. GM# when discontinued was 16177690. It might actually have that part number on it.