EricJ

My service soon light came on my 96 today. It has 42k miles and seems to be running great. It got pretty wet on thursday due to heavy rain storms in the area but the light just came on today. Any suggestions on what might be the problem or anything I can do to remedy the problem before taking it in for service would be appreciated, thanks!!

Eric J

Crushinator

Take off and retighten your gas cap. This has happened to me twice now and it worked both times.

EricJ

I tried that and it doesn't appear to have fixed it. Should I wait a while or should the light go out as soon as I retighten the cap?

RichS

Disconnect the battery to reset the computer to see if it comes back. Otherwise check to see what code was set.

EricJ

Thanks, I will give the battery a shot. How do I know what code was set? Do I need a scanner like autotap to find out?

EricJ

I disconnected the battery and the light went out after reconnected and restarted the car. Should I be concerned or just let it go and hope the light stays off?

BTW, thanks guys for all the suggestions!!!

olephart

You really won't know what the problem was unless you scan it with equipment that will give you the DTC code.

The fact that the light is out means the problem is not currently happening. May come back, may not. Sometimes running over a railroad crossing will set a code.

Just had a buddy with a situation like yours. Code said misfire. Turned out to be a clogged fuel filter and dirty injectors. Light only came on at very high loads.

I probably wouldn't worry too much about it unless it sets a code again.

FrankLT4CE

On my 96 the SES light would come on, usually after filling up with gas. Putting the gas cap on very tightly would usually prevent the problem but not always. No history code was ever detected by checking at home (connecting #4 and #12 at the ALC). No visual defects were present on the gas cap or on the filler neck. But I decided to spend $5 at the local Chevy dealer to get a new gas cap since I had a hunch. Sure enough it solved the problem. I saw the seal was fresher (not mashed down) on the new cap. I still have to tighten it really good as the lettering on the new cap states, but my SES light has never come on again (after 2 or 3 months of daily driving). With the original cap it would come on very frequently.

So if I were you and the light comes on again I think it worth your time to spend the $5 with the hope it will solve your problem and you won't waste as much time as I did. My car had 55,000 on it when my problem started.

In response to your other question, disconnecting the battery cable for 30 seconds minimum is the quick way to eliminate the light, but the light will go out by itself after 3 ? driving cycles where the fault is not detected. Hope this helps. FrankLT4CE :)

olephart

I don't think you can get the codes to display on OBDII by shorting the terminals.

FrankLT4CE

Although I didn't specify, I did mean to say to follow the 96 service manual and also use the buttons on the IP display to get the codes to display. I have had codes displayed by this technique, just never for a loose filler cap. FrankLT4CE

Crushinator

Damn, what a coincedence! :D I had to take my Vette to work yesterday and I stopped and put $10 gas in my car. Five minutes later, the SES light came on. I think I'm gonna take the above advice and buy a new gas cap. This is the third time now and it's getting annoying.

DenverLT4

I agree with Frank mine was doing the same thing until I replaced the gas cap. I would bet that the rubber seal is drying out. I have not had a problem since replacing the cap. 40,000 miles and smiling.

silver & red CE

You can't get the PCM codes this way on an OBDII car, you have to have a scan tool.

Eric

FrankLT4CE

Olephart's post just talked about "codes" and not PCM codes as in the last post. In the factory Service Manual, Book 1 of 2 for the 96 Corvette, page 8D-3 states: the speedometer is used to display Diagnostic Trouble Codes (DTCs) (CCM, RTD, ABS/TCS,SIR and PCM), the odometer displays data, and the trip monitor indicates the system being tested and the test which is being performed. The buttons on the Drivers Information Center are used to send instructions to the CCM when in the diagnostic mode. To enter the diagnostic mode ground terminal 12 of the data link connector. I was answering Olephart's general comment on codes. I answered based on what I read in the Factory Service Manual, and based on my actually doing it.

I am the first one willing to learn from someone else and readily admit I don't know everything. Perhaps you can answer a question that another forum member and I have both experienced on our 96s that have OBDII. The question is why can't we get into the PCM and RTD Diagnostic Modes on our cars. We both had no trouble getting into the CCM (1.X), the ABS/TCS (9.X), and the DERM (A.X) Modes. (X = every number in the mode) However, neither of us was ever able to get into the PCM 4.x, or the RTD 7.x Modes. So yes it is true I could not get to the PCM codes by this technique. But why not? The Service Manual says it should work. Please shed some light here? Thanks FrankLT4CE

However, your post

olephart

Good info Frank.

I am far from an expert - barely know enough to be dangerous. I based my statement on hundreds of post by real experts that said you could not access the DTC codes without a scanner.

I pulled the manual out and looked at your references. I don't know for sure (why should that stop me) but it looks like there are some limited diagnostic functions available as you describe.

These are Chassis items like ABS, Passive entry, etc. (These are items that are not read by most aftermarket scanners without extra $$$).

I don't see anywhere that the onboard system will provide DTC codes for for the engine/emission system (160+ codes for a 96) that are associated with the SES light.

Let me really get out on a limb (flame suit on) and suggest that there are 2 seperate systems in use here. 1. Chassis - controled by the CCM with some info available in the car (and a lot more with a chassis capeable scanner). 2. Engine/ECM - controled by the PCM and accessable only with a scanner.

silver & red CE

Frank,
The 96 manual is wrong. If you don't believe me, disconnect the ECT sensor on the front of the motor, set the SES light and then pull the code. You won't be able to. BTW, there are plenty of errors in the 96 manual. Ever look for the second bleed screw in the cooling system?

If you make it up to the NW 'burbs, I'd be happy to pull the codes, I have a scan tool, the HyperTech PowerScan.

Eric

olephart

Well, I don't know if the features in the manual are implemented, but it seems clear that we are talking about 2 seperate sets of parameters.

My scanner company (Ease) sells a basic scanner that reads all of the engine/ecm stuff that we usually focus on and another package (for big bucks) that reads what they call powertrain DTCs - like curise control, brakes, active shocks, a/c, shift points & times, etc.

A few of the powrtrain items are in the engine package, but relatively few.

FrankLT4CE

Olephart, Eric,
Thanks for the info. Your explanations make sense to me. I agree I have found many other errors in the manual, including the 2nd bleed screw. I did one time get a history code related to when I had my radio controller out, so I do think there are some limited capabilities of the on board diagnostics that do work. I'm glad I have no other problem with my car since I replaced the gas cap. The local Chevy Service Manager seems to know little more than me since he told me his scanner wouldn't find the code either if my technique didn't. FrankLT4CE

olephart

It can get aggrivating using the scanner and the service manual. For some codes the manual basically says "check everything". It does not identify the most likely cause on a complex fault.

That's the beauty of this forum. You can get the primary suspect and usually save a lot of testing.