Service Engine Soon

[caddy]

My Service engine soon light comes on after driving on the freeway at around 65 MPH and about 15 minutes after driving, My Vette is a 94 LT1 6 speed, I haven't pulled a code on it yet but anyone have any suggestions on what could be causing it to come on, and It happens all the time, not just once in a while.
And I'm going to need an inspection here real soon and I don't think they'll pass it if that "Service Engine Soon" light is on.


thanks a heep!

 

[6 Shooter]

Recovering the C4 ECM/PCM Codes

I think U will have to read the code . . .

C4 Corvettes Web Site

The site is really good about explaining ECM/PCM Codes.

Recovering the C4 ECM/PCM Codes

Later . . . . . .
6 Shooter

 

[Yarls24]

Caddy, egr problems. My 88 does the same thing. Probably a code 33. Check out the postings on this. I replaced the egr temp. switch, and the solenoid switch. It still comes on when on the highway like yours. In town driving changing speeds, it will not come on. I just live with it now when on the highway. It may be a bad egr valve, that's what I think mine probably is. My 88 runs perfect, no problems. Egr valve is a pain to replace, that's why I have not done it yet. This may not guarantee a fix. Could be your ECm too. Too many fixes associated with the egr. Good luck.

 

[caddy]

Where is the egr valve and approx how much is it?
thanks

 

[RedRagTop]

My SES was the MAF relays but I'm not sure how it works on a 94...

 

[Yarls24]

EGR valve is underneath the plenum. Egr valve is only like 55.00 bucks, but if you pay to have it done. It will cost you some bucks(couple hundred). I had my intake manifold gasket changed 2 years ago, and I should of had them change the egr as long as they had the plenum off. My mistake. Try the relays, behind the battery on my 88, like RJS said. Relays are only like 10 bucks or so. There are 2 of them.

 

[TODD L GRIFFITH]

Well, I had a 94' Corvette Coupe, wish I still had it. The light is emission related and most likely is a sensor. I would guess an O2 sensor right off, because when they start to go, the check engine light appears intermittently, and they need to heat up before they start to interact with the PCM. Without any diagnostic test equipment it is hard to say without getting voltage readings on various sensors. When I had my 94' I replaced my throttle position sensor, Map sensor and O2 sensors. I didn't realize how bad the car ran with a bad Map sensor, until I replaced it. When the O2 sensor went, I replaced both at the same time just in case. The MAP sensor should read above 4 Volts between terminals A & B with the ignition on. If not, check terminal C for a 5 Volt reference signal. If you find the 5 Volt reading, the sensor is bad. You should get a voltage drop when vacuum (throttle) is applied. The thottle position sensor (TPS) readings depend on what VIN you have. For VIN 8 and J engines with the ignition on, check the voltage at terminal B, for VIN P and 5 engines, check the voltage at terminal C, the voltage should read less than .5 volts. Open the throttle and the voltage should change and increase smoothly. At wide open throttle position, you should read around 4.6-5Volts. Testing the O2 sensors becomes alittle more involved due to VIN heated and non heated O2 sensors, some having two sensors ahead and behind the cats, either side. even so, I would suggest a replacement every 30,000 miles. Very easy to do. The C5 was a god send with its DIC. Throttle position sensor is available at AUTOZONE and PEPBOYS for $50.00. MAP sensor available at the same stores for around $40.00. O2 sensors available at same stores for around $50.00 each. Not bad considering what the dealer would charge, but the advantage of the dealer is all the diagnostic test equipment, and finding the problem fast. TPS is located on the right side of the throttlebody sitting in the drivers seat. Map sensor located located on top of, and right side of throttlebody from drivers seat. O2's located fore and aft of the Cats in the exhaust pipe. Sorry if you knew this already. To get voltage readings on a sensor that is plugged in, straighten out a paper clip and insert it in the terminal from outside the plug where the wire goes in, behind the plug. Good Luck! An electrical test meter is recommended if you have an LT1. Also the GM Corvette 84'-96' repair manual where I got you the info.

 

[Hib Halverson]

It's pointless to speculate about what's turned on your MIL. You need to find out what fault code is set in the ECM.

96 is an OBD2 car so a scan tester is required to get the code. Do that and post the results and then, maybe, we can offer you some useful information.

 

[KOPBET]

It's pointless to speculate about what's turned on your MIL. You need to find out what fault code is set in the ECM.

96 is an OBD2 car so a scan tester is required to get the code. Do that and post the results and then, maybe, we can offer you some useful information.

And from what I hear, Auto Zone will do this for free. Go for it!

 

[TODD L GRIFFITH]

Useless Information

Could be all useless information, but I agree get the code first. Nice C6 article Hib, by the way. Hey Autozone will scan it for free is about the best information I've heard, beats the hell out of what I said.

 

[kenwa]

Like Kopbet said. Any time I get an SES, I go to Autozone.
I haven't had it happen on the Vette.

 

[caddy]

Thanks, I'll run by Autozone and see what kind of code gets pulled, heck if it's free.............WHY NOT?

Thanks again

 

[caddy]

It's true Autozone will pull your codes for free, however only starting in 1996 and later...............no 94 s and earlier, I went today and got the bad news..

And from what I hear, Auto Zone will do this for free. Go for it!

 

[Rabbit]

I think U will have to read the code . . .

C4 Corvettes Web Site

The site is really good about explaining ECM/PCM Codes.

Recovering the C4 ECM/PCM Codes

Later . . . . . .
6 Shooter

ttThat site has been off for a while. Sometimes up & sometimes down?