1996 Monte Z34 : Service Engine soon

My service engine soon light goes on and off intermittantely.
Sometimes its off for weeks then comes on for weeks/months.
Then will go back off been doing this for the last several years.

Well its inspection time and the thing has been on for a month now, and it wont pass this way so i figure might as well fix it for good. Im figuring its an 02 sensor.I was wondering which sensor is the most common to fail, the one before or after the cat ????

go to an autozone and get it scanned for free
instead of guessing whats wrong:)

Mine is the Ground wire on the EGR..had it scanned, I never bothered fixing it. I replaced my O2 sensor and that never helped. Before the cat is $55 from Napa. Mine doesn't have and after cat sensor.

mine isnt a z34 just an ls but i have changed both of the o2 censors and the egr valve and Auto Zone's machine reads 3 codes...
o2 censor #1, mutli misfire, and egr valve.
I have changed both o2 censors and the egr valve and still i cannot get it inspected because the light is on. I have been told to get a diognestic test done but that is $65 at the dealership. but if you say that is was just the ground wire on the egr is that hard to fix? I am trying to keep from taking it to the shop because i am tire of hearing about the small oil leak i have.

mbrdmyr,

Just because a scan tool will give a certain code,(in your case O2 and EGR)it doesn't mean that it's the part itself gone bad. When diagnosing a vehicle, I'm required to check everything from the old sensor, the wiring harness, all wires, and finally the ECM. When a scan tool gives you a code, it means the computer saw something wrong like high voltage, no voltage, out of limits. melted/shorted wires can cause this as well as a faulty connection at the harness. Hope this helps

I bought my 96 Monte Carlo New in 1996 and started having trouble with the service engine light coming on and had it checked.At first they said it was the oxygen sensor and replaced it.Light came back on and took it back to dealer and by the time I got there the light went out.They said they would keep and drive it for 3 days and see if they could solve problem.When I picked it up they said they could not find anything and told me I had bad gas.I told them that I got gas with all of my cars at the same place and I was not having problems with them.Light kept going on and off over the next few months and I said the heck with it because now it was out of warranty.Later I got a recall from GM saying they had problems with the air pump trapping moisture and causing the service engine light to come on.I took it to the dealer and they put a kit in it to help take the moisture out and then until one of the spark plug wires went bad the light stayed out.The moral of this story is see if your 96 has had the recall for this repair by having the dealer run your Vin #.It works for me and it may be your problem.Good luck.