Chevrolet Repair: Corvette, catalytic convertor, oxygen sensors

Question
QUESTION: James,

I am also a volunteer on this site under electrical and electrical motors.

I appreciate you taking the time to answer questions and understand exactly what you mean about not being able to see or hear the vehicle.

I have a 1996 Corvette. It has 66,000  miles and I am the third owner.

I drove the car for about a week and the "check engine soon" light came on.

I have had it to four mechanics. The first says it is the oxygen sensor. The second said it was the body module [computer module under passenger dash.]

I had the module replaced and after driving it home it came on again. I took it back and they pretty much said they have no idea. I just took it to two mechanics, the first said it was a catalytic convertor, but they couldn't do the work, but they gave me the print out.

I took it to the next and gave him no prior information just said the check engine light comes on.He says the computer code was a bad catalytic convertor.

He replaced the convertor and the oxygen sensors. [I hope]

I drove it about 20 miles shut it off, started it again and the light comes back on.

I have to take it back to him tomorrow and see what he says,but there is more to this than meets the eye.

It just seems that because they disconnect the battery to perform whatever repair it kills the check engine soon light and they are satisfied it is fixed.

Twenty miles later it is back on.

It runs fine, everything else in the car operates and has no problems.

It has new plugs, wires, body module, convertor and oxygen sensor. There is something about a 96 that must be a bug in all of them.

Ever heard of such a thing?

The module was over $1000, the convertor was over $1000.00, and I still have a check engine soon light that comes on.

It has to warm in twenty miles or so of driving, just regular driving no hot rodding no nothing.

Something seems to be heat related as it seems that once it is warmed up the light is on again.

It is driving me nuts and broke...........

Oil has been changed, all fluids have been changed, all computer diagnostics run several times, and I still have the light.

It does not back fire, does not hesitate, starts right away, gages are all working and within normal range.

I will be taking it back tomorrow for the converter, the light is on and that was the complaint I took it in for.

Any suggestions, know any Corvette guys who have run into this?

It appears it is nothing at all serious, the light just comes on and won't go off.

I was a mechanic for many years before computers on board so I am lost in the new technology.

If you can tell me where and what to check, I will pass it along when I take it back or do it myself.

Again, it is a mystery that has got by several good sized highly recommended shops and still the light comes back.

I appreciate the thought if you have any on this subject.

Thank you so much!

Will
ANSWER: Hey Will,
Have you done anything to the car such as install a radio or maybe a computer chip for performance?
Do you or are you able to get the codes from the on-board computer?
Does it smell like gas from time to time?
Is your gas tank cap faulty?
Your car does what is known as a fuel system pressure check for the gas tank often, if it comes back detecting a fault, it will trip the light on.
Remember, the only reason that a check engine light will come on is if the hydrocarbon levels exiting the vehicle are at a high level.
There is something that peaked my intrest though,,,
the fact that you have to drive it for a while for it to warm up.
Have you recently (besides what you have mentioned) had any work done to the car such as thermostat replaced?
Valve cover gaskets?
Or any work that blue RTV silicone that is not sensor safe has been introduced to the system?
A lot of questions I know, but I have to (as you know)
Thanks for helping out answering questions with me, and we will figure out whats going on with your car.


---------- FOLLOW-UP ----------

QUESTION: Thank you and ask away! I do not have a device to get the codes. I am only told from two different shops that their codes show bad catalytic convertor.

So I had it replaced. NOW I might have jacked you up saying it had to warm up. After the body module was replaced the light was off, I drove for about 20 miles, [I didn't know I would need to measure mileage I thought it was fixed]. Parked it let it sit, got back in and started it ant the light was on. Long story but this guy was the body module replacement guy and he did a crap job from leaving the t-top roof bolts out to carpet to everything that told me it was a slam dunk job.

Then I go to like a tires plus to have an oil change and a computer read out, they say it needs a cat convertor but were not equipped to do that kind of work.

So I get another referral to a shop from several people, he calls and says the light is on as the code says bad catalytic convertor.

I pick it up today and drive approx 20 miles back to work, shut it off, go inside for maybe an hour, come back out start it, and the dame light is on "service engine soon".

I am beside myself.

I own both original Y platform manuals for the 1996 vet.

I start to read them and crap, it it is like reading boolean algebra.

But I notice one thing, reset the codes by removing the negative battery terminal only.

I just did that and the light is off. I started it twenty five times, drove it for about 10 or 15 mile and brought it back home. Let it sit. Started it no light. Still no light.

So I am going to let it cool for the next few hours or in the morning and start it again and see if it comes back on, if it does it goes back to the catalytic convertor guy.

But I can't get it to come back on tonight after only removing the negative terminal cable from the battery and I cleaned it while I was at it. Not excessively corroded at all, not anything I would normally worry about, it looked pretty good.


No rich gas small.

Gas cap seems fine and locks tight, no threads worn or anything that looks wore or cracked,

No thermostat replacement. No leaks in the coolant and no change in the normal operating temperature since I have owned it.

No valve covers or other parts where RTV could be used since I have owned it.

It has really not been touched except a set of plugs and plug wires.

It runs like a top, starts, everything works, it rides better than my buddies 2003.

It is a 6 speed 350, t-top couple with 66,000 miles.

The Y Platform manuals say the light could come on from a list as long as my leg in number 16 font.

Is it possible that the negative cable cable removal, which as I read it, clears all the old codes regardless of codes, and empties it's memory?

I can't imagine that is all it is after all this and expect it to come back on tomorrow, I will drive and park it as many times as I can.

I will recheck the gas cap and see what happens.

It appears there is a way to get certain codes from the dash by shorting across a couple terminals at the body module connections?

Then there are all kinds of code readers I can buy I see advertised.

So with all the events since I first wrote does that give you any more ideas where to look it the light comes on again?

Please ask away I know the simplest things can be the culprit, and this car is one big computer.

Right now it looks like I killed the light with the 30 second removal of the negative battery connection.

Possible that I cleared all the old codes created by a faulty convertor, the mechanic said it had no guts left in it at all, completed cracked up and blown out the back was his comment.

But I have duals and two convertors and only one replaced, I asked if one is gone why would the second not be far behind? He says it was not normal wear more of a possible fracture in manufacturing and it got worse and worse...........

I was working on cars when I was rebuilding 289 V8s in Mustangs.

It has been a while. The Corvette has been trouble free other than the damn light, the gage says 46 MPG at about 67 miles per hour in 6th gear.

Right or wrong it really does not use gas like I would have thought, I did my own calculations and I get right at 17 to 18 miles per gallon by the standard method.

I would really like to hear your take on clearing old codes and the removal of the negative cable to do so.

Maybe neither of the others had any idea that was the procedure.

But that is how I read it.

Appreciate all your time!

Will

Answer
Resetting the codes by removing the battery cable isnt something that I would tell someone to do. And yes, you have probably erased the codes from the computer. I would almost bet the light will come back on though.
If it does, and it comes back showing a catyllitic converter, check the EGR valve to see if it is operating. If its not, that could be the reason why your converter went bad. Not a bad idea to have the other converter checked as well. Please keep me up to date. I will look forward to your next writing either good or bad.