A little history: It's a '96 six-speed. When I bought it, the water pump, opti, and plugs and wires all needed to be replaced. No problems since then, other than my little dry-cell battery running down constantly.

My check engine light has been on ever since I got the car, and I recently learned how to make the car display its trouble codes. The CCM reported in its code history the codes 31 through 38, as well as 71 and 72. Ten different trouble codes.

I've searched around for guides on what these mean but I haven't found 31, 37, 38 or 71; and 72 seems to be a code that only applies to automatics. I guess these guides don't apply to the '96 cars. Can someone tell me for sure what these codes mean and what's wrong with my car?

 

This may help.

http://forums.corvetteforum.com/show...ight=ccm+codes

 

You can't pull codes through the display on 96's. You have to use an OBDII code puller of some sort. Autozones around here will pull your codes for free.

Your Codes should be something more like P0361 or some such.

 

I can't? Well... I did.

I followed the method listed at the bottom of this site:

http://www.corvettephotographs.com/c4vettes/codes.htm

Also, I forgot to mention that my engine pings pretty bad when I hit the gas. I was hoping that the diagnostic codes might point out what's causing this.

 

He is talking about CCM codes which you can display by grounding terminal 12 of the ALDL. CCM codes are two numerical digits. I think you are referring to PCM codes.

 

Do yourself a favor and purchase from eBay, an OBD11 code reader.
They sell for $20.00 and comes with a book with all the codes and a brief description of the causes. They also erase all storred codes.

 

Both CCM and PCM codes, as well as ASR and DERM codes are all displayed on the speedometer using the method I pointed to on that website. Read the website if you're not sure what I mean. And you are correct, all the codes I got were for the CCM module, displayed as module 1. The PCM and everything else reported no problems.


As far as I know, a generic OBD 2 controller would display the exact same data I pulled, only in a more generic format instead of the way corvettes display their codes, meaning that buying one would be redundant. Cold_B, I assume that you were expecting the type of codes one of these devices would display; you can indeed read codes without one, as I have done. It's just in a different format. Check out that website.

I still have no idea what the particular CCM codes I got mean or why my engine is pinging when I gas it. Once again, the codes are 31-38, 71, and 72. Any ideas would be appreciated.

 

I don't think that you can get the correct codes from the display like that. I'm pretty sure that when they switched to OBDII they added another digit to the codes, and thats why they wont show correctly on the display (thats from what all I've read here on the forum). I believe that the codes you are seeing, are all the code.

OBDI and OBDII are different, having OBDII is one of the things we havet to deal with since we have 96's, but I think its well worth it. I don't have to go under the smog machine for my inspection, but 95 cars and older do. They just check to make sure my SES light isn't on, and the computer has completed its full diagnostics. Much much better IMO, especially once you start modding.

If you were to pull the codes with a code puller from the OBDII port, it would give you specific codes like the P0135 which have entries in the FSM and will give you detailed instructions on what to do.

I'd buy a cheap OBDII code puller (I've heard of them for like $20 from Harbor Freight) or call you local parts store and they should pull them for free (or loan you the tool for free).

There are no codes in the FSM that are anything like the 31-38, 72, and 72 that I have seen anywhere in there. The codes that it does have are the P0136 or something similar.

While you may be able to get something on the display by the paperclip method, I don't believe they are of any use to use since we use OBDII.

 

From my FSM which you should buy.

31-LCD Data Circuit Shorted to B+ or CCM Internal Open
32-LCD Data Circuit Open or Shorted to Ground
33-Data Clock Circuit Short to B+ or CCM Internal Open
34-Data Clock Circuit open or Shorted to Ground
35-Data Strobe Circuit Shorted to B+ or CCM Internal Open
36-Data Strobe Circuit Open or Shorted to Ground
37-M Clock Circuit Shorted to B+ or CCM Internal Open
38-M Clock Circuit Open or Shorted to Ground.
71-LCD Dimming Output Circuit Shorted to B+ or CCM Internal Open
72-LCD Dimming Circuit Open or Shorted to Ground

Sounds like someone took a machette to your wiring harness! Good Luck!

This will do you no good without a FSM.

 

Thanks, sounds like it would be a good idea to invest in an FSM and a code puller.

 

Get out your FSM and read pages 8D-6 & 8D-7. These CCM codes 13-81 can be pulled with a paperclip.

 

Wrong!!

 

Well, I was partially wrong. You can pull codes throught the display, but they are NOT the major OBDII codes which will help you diagnose most major engine problems. Those code HAVE to be pulled from the OBDII port by a OBDII scanner of some sort.

I never had seen the 8D section.

If your experiencing Pinging, then you need to pull the OBDII codes, which will tell you what is causing that. Those codes are like P0325 - Knock Sensor Module Circuit, or P0506 Idle System Low - IAC Responding. Those will give you a much more detailed view of my your engine is having problems.

We were arguing over to different things, for the most part. I was wrong in that you can pull codes through the display, but they are not the important OBDII engine codes, those codes are only for the Central Control Module (which controls display functions) where as the OBDII codes are for the PCM (Powertrain Control Module) and those codes are for engine malfunctions.

If your having pinging, I suggest run premium gas to see if it goes away, and have your OBDII codes pulled by either borrowing a OBDII code scanner or buying one.

My first guess as to why you have pinging would be your running to low of an octane gas, or your knock sensors are bad.

 

We weren't arguing about anything. When you tell someone they are wrong on this forum, it helps if you are right. His car is an LT4 which requires premium fuel.

 

Actually, the fuel might have something to do with it. Recently the car was in storage for two months, and the gas consequently became two months old. I've filled it up twice since then but it's still pinging.

Problem is, I'm not sure if this is a new problem or not. It pinged before, too, but that may have just been when on the rare case I put the wrong octane in. I can't remember if it used to ping all the time or just on those occasions.

 

What grade octane have you been putting in? How much gas is in your tank right now? If its fairly low, I'd fill back up with premium if you haven't been using premium (93 around here). After the fuel has a little while to mix up, then your octane should be somewhat higher depending on what you've been running.

 

Cold_B, the last several tanks have been premium. The octane is fine, I'm just worried that running really old fuel through the car may have messed something up. Other than that I have no clue what might be wrong.

So are you saying my trouble codes I'm getting have nothing to do with the pinging?

Lefoy, I'm confused. The FSM's descriptions that you have me for these CCM codes seem to be all about display wiring and stuff, but a few of these very same codes are listed in the haynes manual and elsewhere, which are described as dealing with the MAF and other stuff in the engine bay.

According to that website I pointed to earlier, the CCM codes a '96 gives should mean the same thing as in all the other models...is that website wrong about this?

 

I don't see what you could have messed up by running old gas. If it was the gas it should have gone away with the new tank.

If your having pinging and running premium gas then I would suspect the Knock Sensors, or the Knock Sensor Module.

The codes that you have pulled are for the CCM, not the PCM. The PCM is the computer that controls the engine, the CCM controls the LCD speed display and all that stuff. The codes your getting don't have anything to do with the pinging, because your pulling the wrong codes. I believe you can pull the OBDI codes like that on 95 and older cars, but not on our 96's.

The CCM codes might mean the same thing as other models, but that doesn't have any connection to the problem your having. You need to pull the OBDII codes from the OBDII port using a scan tool of some sort. That will give you engine codes to help you diagnose why your car is pinging. The Codes you will get from the OBDII will be like P0325, which means Knock Sensor Module Circuit. Those are the codes that will help you. You may have problems with your display, but that is NOT effecting your engine.

You should never hear pinging in an LT4 if the knock sensors are working correctly and your running gas with enough octane. Since your running premium, then that leaves the knock sensors as a culprit. It should be possible to run regular gas in a LT4 with no pinging, but the computer will have pulled out alot of timing, leaving you with alot less power, and noticeably lower gas mileage.

Go to your local Autozone, I count 18 near Louisville from their website, and the will pull your codes for free. Just walk in and tell them you would like your codes pulled, and its a 96, which is OBDII. Someone will go out to your car with you, plug up the code puller, put the key in the ignition and turn it to acc mode, and then the code puller will display the list of current and history codes for the engine.

That will give you what you need to know for figuring out whats going wrong with your car.

Make since now?

 

Yeah, you're right, and I'll hit up autozone as I'm sure they'll know what the codes mean.... but I'm still confused by what you're saying.

According to that website, the display does show PCM codes, if there are any, using that method. The display shows the module number (CCM or PCM or two others) followed by any trouble codes for that module. When I use the paperclip method, my display does just that, in the exact way the website describes - it displays the number 1 for the CCM along with any codes, then the number 4 for the PCM along with any codes, then the number for the other modules followed by any codes. Read the bottom section of the website if you're still not sure what I mean.

When my display got to the module number for the PCM, it displayed ---, meaning that my PCM detected no problems. Are you saying that a '96 car will never properly display its codes from some of its modules? That would make an entire section of that tutorial wrong.

 

From everything I've read here on the forum, it seems that that website is wrong on a few things. I've always read on here that they went to the OBDII connector on the vette's midway through the 95 production, but still used the OBDI computer. The 96's all had OBDII ports, and used OBDII connectors.

I've always read that OBDII codes couldn't be pulled using the paperclip method because OBDII codes have more characters. As far as I know they one started making cars using OBDII when it became federal law (or whatever it is), in 96.

Your getting something from the display obviously, but I would guess they are the CCM codes, so I would guess that it can display some codes of some modules on the display, but I believe the PCM codes are excempt from that.

I'll see if I can't play around with my car tonight. I bought a Autotap just the other week and I'm still learning about it. Its very neat, and very powerful.

I find it pretty hard to believe that the PCM isn't throwing any codes if you are hearing pinging. It should be throwing codes either for knock sensors, or a engine misfire, either on a specific cylinder or the whole engine.

Maybe the display shows --- because it really cant talk to the PCM in a way to read the codes, or it knows it can't display them. I've never played around with the paperclip trick because there is a autozone about a mile and a half away from my house, so there really wasn't much point.

Please post up what you find out at Autozone, it will be intresting to see what the truth about all this is.