Service Engine Soon Light

I have a 1996 silverado ext 5700 vortec. Sometimes the "service engine soon" light comes on and stays solid for a couple of days and then goes off. It will usually stay off about the same amount of time. What could be causing this intermitten activity? Also, should I have it checked at the dealer so they can read the codes?.

The PCM has seen a fault somewhere in the emission system. The PCM stores a DTC to help pin point what circuit or sensor the fault is on.
You will need to take it and have someone pull the code and diagnos the problem.
I would reccommend taking it your dealer....but I am biased :grinyes:

So, I ran by Autozone on the way home tonight. I found out that the reason for the SES light was that bank 1 & 2 are running rich. My next question is what do you think would cause this? I was think of running some injector cleaner or marvels mystery oil through and see if that helps. Any other suggestions would be appreciated. Thanks.

Both banks reading rich would indicate unburned fuel.
Raw fuel could be entering the engine from the regulator.
Fuel pressure is too high.
Blockage in the intake.

The use of "snake oils" will not fix the problem, you need to have the problem diagnosed and repaired by a reliable and knowledgeable technician.

The fuel pump was replaced about 2 months ago. do you think that this error has something to do with that?

Probally not.
When the PCM sees the fault, it will turn on the SES light. At the same time, the PCM stores data (called freeze frame and failure records) relative to the fault. It gives the tech an idea of when the fault occurred to help narrow down the diagnostic process.
This allows the tech to operate the vehicle in the same manner you were when the fault occurred (this is extemely helpful with intermittant problems).
For some reason there is an introduction of raw fuel in your engine that the O2 sensors have picked up on. Could be a schewed sensor reading, failed part or even a wiring issue.
Thats why I recommend having a factory trained tech look at a problem like this. He can look at the data and determine what is the root cause of the failure instead of just throwing parts at it.

And you wonder why I get the big bucks :rofl:

And you wonder why I get the big bucks :rofl:

Is there really alot of money to be made as an automotive technician?

Anyway thanks for all your help. I do plan on getting the truck to the dealer for a check-up as soon as I can afford to.

You obviously missed the sarcasm in my last post. :iceslolan

UPDATE: The light came back on (as I expected it would). I called the dealer and they want to charge $75.00 just for the diagnostic test. once they diagnose the problem then give me an estimate. I can't image that it would be inexpensive. I guess it beats having a truck payment every month.

I was returning the sarcasm.

UPDATE:

I am still having the same problem. I took the truck to a mechanic who did the diagnosis. Sure enough he said it was running rich. He said to start with a tune-up. I wasn't really happy with his response but I did the tune-up anyway. After the tune-up the light came back on. I took it back to the mechanic and he hooked it up to his computer and took o2 sensor readings. He showed me that they were slowly coming back to life and he recommended that I do a fuel system flush/clean for $178.00. Not sure that I like that idea either. Do you think I would benefit from this or should I just go ahead and replace the o2 sensors?

UPDATE:

I am still having the same problem. I took the truck to a mechanic who did the diagnosis. Sure enough he said it was running rich. He said to start with a tune-up. I wasn't really happy with his response but I did the tune-up anyway. After the tune-up the light came back on. I took it back to the mechanic and he hooked it up to his computer and took o2 sensor readings. He showed me that they were slowly coming back to life and he recommended that I do a fuel system flush/clean for $178.00. Not sure that I like that idea either. Do you think I would benefit from this or should I just go ahead and replace the o2 sensors?
You asked me earlier and I quote "Is there really alot of money to be made as an automotive technician?
I would say that your mechanic is making a good living off of you" :lol: :lol: :lol:

I call B*LLSH*T on any mechanic that tells you that a tune-up will fix a SES light.
Please take my advice and before you waste any more moneyor install any more parts that you may not need, find a knowledgeable, factory trained and trustworthy tech to diagnos the cause of your rich conditon.
Read back a couple posts and look at my suggestions on what could be causing your rich condition.

GM Merlin:
I'm having the same issue on my '03 Silverado with a 5.3. SES light coming on with P0157 suggesting fuel is too rich. Been doing this since 4,000 miles; has 8k on it now. Would a rich fuel mixture or high fuel pressure be a source of rotten egg smell out the exhaust or spark detonation sound during acceleration? I have both symptoms.

Actually, the P0157 is for a lean condition.
You could have a vacum leak, low fuel pressure or a sensor wiring problem.
Lean fuel mixture will cause a rotten egg smell and detonation.
Since your truck is still under factory warranty, take it back to the dealer and have them look at it.

Merlin, How is a tune-up a waste of money? whether or not it fixed my "SES" problem I was due for one anyway. My logic tells me to do the obvious things first.

Merlin, How is a tune-up a waste of money? whether or not it fixed my "SES" problem I was due for one anyway. My logic tells me to do the obvious things first.

I never said a tune-up is a waste of money. I'm glad to see people who keep up with the maintenance on their vehicles.
My quote "I call B*LLSH*T on any mechanic that tells you that a tune-up will fix a SES light." I stand behind.
You took your vehicle to the man to diagnos and repair your SES light. You said he recommended starting with a tune-up....The light came back on, SO he didn't fix your problem.
I'm not trying to get in a pissing match with you about this. From here it looks like you are being taken for a ride.
The comment "I took it back to the mechanic and he hooked it up to his computer and took o2 sensor readings. He showed me that they were slowly coming back to life" I cant buy...The heated O2 sensors are almost instantanious in their response. Even with a flooded engine, a quick roadtest will clear out the system and the sensors will be toggling.
There is a diagnostic procedure for determining the cause of a rich condition. No where in the procedure does it mention a tune-up and injector cleaning.
Dude, you asked for advise and you got it. And like I said earlier,from what I'm reading it looks like you are being taken for a ride.

What was the final verdict on what was wrong because I am having the same problem?

It was the fuel pressure regulator. A little bit of a pain to get to but it solved the whole running rich problem.