I have a 94 3.4, I am getting the "Service Engine Soon" light/ It only comes on after driving down the highway when letting off the gas. I have tried to check codes with my OBD I/II reader and get nothing. I have tried to get the car to self test by using the jumper wire and nothing. It is suppose to give me a 12 code (OBD I) if everything is okay but I get no flashes whatsoever. After turning the car off for a few minutes, the SES light goes off and stays off till my next trip down the highway.

Searching thru threads here I see this problem has come up before. I took the advice in a thread and swapped out the EGR valve. I got a used EGR valve and get the exact same problem at exact place on highway.

Any other thoughts????

 

You get a code 12 and that tells you the comp is in its diag mode. No 12, no diag. You did try a jumper in a+ b terminals or I think its 2 black wires and then turn the key on engine off? Perhaps the service engine light is on because the computers diag mode is not funtioning?

 

Yeah I tried the jumper wire, I even blew 25 bucks on the acutron plug that is nothing more than a jumper wire to plug into the test connection. According to the Haynes manual, this should put it into test mode. I think this may be different problem from the light coming on when I left off the gas pedal after traveling at highway speeds.

 

yea... the light came on for me too. Mine was probably a problem with emissions. When the computer detects a problem or that a problem might occur it will turn on that light. When you restart the car the computer checks for that same problem, after so many successful starts and the computer doesn't detect the problem the computer will clear it thus the light will go off.

 

The 94 & 95 Camaros have an OBDI computer but use an OBDII connector. This causes a problem with most DIY code readers as they can't communicate with the computer properly. A professional grade scanner such as OTC has no problem. The other problem is that, contrary to what the manuals state, you can't flash the codes in these cars.

 

I will take it to Chevy dealer and see if they can get a code read off this thing. The SES light still comes on as soon as I let off the gas at highway speed. I can turn engine off for about 30 seconds and light is gone until the next time. I have swapped out the EGR valve with another used EGR and I cleaned the throttle plate for IAC.

 

if you get it scanned and its an egr flow problem its probably a restricted(carbon build up) in the egr passage. remove the egr valve & the throttle body. inside the plenum you'll probably see some carbon build up adjacent to the egr valve. start picking it out (hard & crusty stuff) then use a coat hanger or something bendable and sturdy to clean the passage from the valve through the plenum. a little carb cleaner might help loosen it up alittle. let me know what you find.

 

I got the codes read. I had 75- EGR valve #1, 76- EGR valve #2, and 77- EGR valve #3. Any Ideas??

 

The EGR valve is not working.

1) Make sure fuse #6 is good
2) Clean out EGR as AL69z28 indicated
3) Replace EGR if the codes persist

 

Fixed it! aj69z28 was dead on! He needs to patent a coat hanger as a special EGR valve cleaning tool. I took the EGR tube that goes into the intake manifold loose and removed the throttle body. The little hole in the intake that is the passage way for airflow to valve was completely blocked off with crud. Alot of coat hanger action, crud removal, carb cleaner, and a high flow air nozzle blew it clean and now I don't get the engine light.

Just make sure that you check the radiator cap after your done climbing around cleaning the EGR passage. I knocked my radiator cap loose in the process and didn't find out until I was 10 miles down the road and steam poured from under the hood at a red light...but that is another story!

Thank you everyone for your help with my engine light issue!