JAKE

As I understand it, when the Service Engine light illuminates, the car's computer automatically switches to a different 'mode', which ignores 02 feedback and causes the engine to run on pre-programmed computer tables for fuel and timing.

I don't recall if it's "Limp Home" or "Open Loop" mode, ( computer has several different "modes") but the system will not remain in Closed Loop mode. This is why the engine runs better with the light "On" since those tables are a better fit for engine operation.

Jake

West Point ROCKS!

MikeC4

You will definately need to jack up each side to be able to get to the exhaust pipies where they are mounted. They are a bit tricky to get at because they are mounted in limited access area. The best tool I ever found to remove C4 O2 sensors is 7/8" stuby open end wrench. Disconnect your negative terminal battery as one of the sensors is close to the starter motor and the 12V live wire that attaches to it. I was laxy once, and arced the hell out out of the wrench and started terminal. Nothing damaged, but scary.
Again, inspect the wire harnesses carefully and make sure that they are not near or touching exhaust.

Here is a pic of your best frien when removeing/installing an O2 sensor:

joe3906

Thanks God you have a mechanic buddy. Imagine the dough rey me you'd be spending had you not? I'm not handy either, but when you got get under to save $300 bucks for a minor problem, guess what, "you go under." LOL.

Joe B.

MikeC4

When the light is "on" the O2 sensors are ignored and the car runs pretty good from the lookup table values. When the light goes "off", the PCM switches back to "closed" loop operation where the O2 sensors are used for AFR calculations. This is where the bad O2 sensor is indicating constant or prolonged "lean" condition. This in turn will lead to richer AFR causing the poor sluggush condition that was reported.

shhaker69

ok, so i got tired of waiting for my buddy, the guy down at the parts place rented me a actual O2 sensor wrench, thank god. the driver side was the one that said was bad. It was all sooted up. the passenger side was a biotch to get to. but it was not all sooty looking. But I changed both anyway. The code is gone and all seems good in my C-4 world once again!! Thanks for all the help and Im truely grateful for the corvette forum!!

STL94LT1

ambassadorgodzilla

Oh, Lord, please tell us how you raised the car to get underneath it...
You did find the "jacking point"(s) where they're labled, please, please.....

STL94LT1

MikeC4

STL94LT1 - That is a gorgeous White C4 !!!!!

JAKE

The only time I use the factory jacking point is when I'm using the factory jack.

In the past, my "real" floor jack tended to bend the pinch rail, so I choose the flat, steel area just inboard of the pinch rail, toward the rear of the front tires.

I even tried putting a piece of 2"x4" on my jack and still used the pinch rail, but the rail cut through the wood, which caused me, what you might call EXTREME ANXIETY when the wood let go and the car dropped a bit.

For the rear, I use the - how can I describe it - triangular shaped, steel chassis point with a piece of 2"x4" on top of my jack "disc". The round thingy that's removal.

If your car has been lowered or the jack won't slide under, just drive it up on two pieces of 2"x4" or 2"x6" to elevate the car and give you the clearance you need for the floor jack.

If it's really low, like my 86 use to be, I screwed together three pieces of 2"x6" boards in a ramp style to drive up on. Lowest board about two feet long, middle board about 18" long and top board a 12" or so long. Sort of like a stair-step arrangement.

But that's just me.

Jake

West Point ROCKS!

STL94LT1

Thanks!!

shhaker69

I was nervous about it but i used a floor jack and jack stands!! It was all good, that was one of the reasons i wanted my buddy to come over, to keep an eye on me while i was under there. It all worked out i the end. I figured out i need a floor jack like the one you have!! The one I have is kinda narrow. hans

Nick DL

This thread is just what I needed. I drove the vette this morning and my light came on and was able to figure out the codes from this thread, thanks.

The codes that I got were H64 on 4 which is the O2 sensor, so I would imagine that I need to replace the O2 sensor.

The 2nd code that I got was H72 on 1. I believe this is Vehicle Speed Sensor Loss. What exactly does that mean and what do I need to do to fix it? Or will this be fixed when I change the O2 sensor?

I appreciate your help, thanks.

Nick

JAKE

First thing I'd do is clear the codes and see if they come back.

If one or both do, I'd attack the 02 sensor problem first; sometimes fixing one will automatically fix the other.

Jake

West Point ROCKS!

Nick DL

Thanks, I will do that and see what happens.

JAKE

Does anyone have a full listing of the codes for the 1996 Vette? Some of them are different from earlier engines.

I'm looking for H71, H72, C71, and C72 my son's 96 just threw last night.

Thanks,

Jake

West Point ROCKS!

onedef92

Peep this link. Should help a lot.

http://www.corvettebuyers.com/ecm.html

barry96

I have a service engine light that I've ignored because it usually goes away after a few more miles. But I'm do for an inspection so I've got to clear this up.
1. Last time this happened a few years back, someone told me that the 96 does NOT report all the codes to the dash. (I get a C12 anyway.) Can someone confirm this?

2. My mechanic's computer flagged it as an O2 sensor but it went away on it's own but it's back this year. I haven't driven the car very much over the past year.

2. If I clear the "service soon" by disconnecting the battery, what are the driving procedures for getting the computer 'ready' again for inspection?

Thanks.

onedef92

Don't forget the anti-seize compound for the new sensor. And if the connector pigtail breaks in your hand as you go to unfasten it like mine did, you can buy them at NAPA Auto Parts stores.

lillys95

After driving 25 or so miles on the highway my Service Engine Soon came on. Then after turning around to head home the red Check Gauges light also came on. Once the car sat over the weekend both lights are now OFF.

The mechanic says he can't read the codes unless the Service Engine Soon or Check Gauges light is still ON. That means I have to go run the highway again. I did take photos and run video when this occurred.

Aren't the codes stored? Is he correct?