check engine soon light

I keep getting a check engine soon light on my truck. I have taken it to my warranty mechanic to look at and I was told the code that came up was for an evaporator control problem. He told me the purge valve may be bad. The dealer doesn't want to have the mechanic do anything until I get a hard light that won't clear. Any suggestions on what to do or check. I would appreciate any information anyone could give. Thanks in advance.

I cant tell you what to check but I can say that my light comes on and off everytime I drive it. I have been told by my dealer that this is normal under the kind of driving I do(stop and go). When I get out on the highway it usually goes off. Most people that I know that own chevy vehicles have this problem.

i had the same problem with my '98... i ended up traking it to a mechanic who told me i had a cylinder misfiring...it ended up costing me $500 for new wires and sparkplugs...does that sound right to any of you??

:nono: Stumax-- You don't seriously mean to tell us that you paid $500 for a set of spark plugs and plug wires do you?

well what should it have cost? i guess i overpaid?

Man you overpaid about $400. did it solve the problem???

When I test drove my Silverado before I bought it, the light came on.
When I got back I told the salesman I wanted the truck but not until
that light was shut off. They plugged it in, turned out to be a misfire.
They said this happens with short trips, (testdrives).
It has never came on since...
:2cents:

It took me a year and a half and three diferent mechanics before I finaly did a leak down test and found out I have a leaking or buned exhaust valve. A misfire can be caused by all kinds of different things, and it seems that they like to through money at it before they figure out what the real problem is. If you can't figure it out soon you might try a leak down test just to eliminate a larger problem, before you replace any more that does not need to be replaced. I had a friend that was able to do it for me, but I could have had one done for $50.00. So short story long, with all the money that I spent getting nowhere I could have just paid for a leak down test, pulled the heads and had a valve job.

That's a very familular story. I had a misfire for over a year and three different trips to three different dealerships. They all replaced things that did not need replacing. The third mechanic said I needed a new fuel pump, what he didn't know is..I just put a new OEM fuel pump in not more than 6 months ago. Turned out to be a burned exhaust valve in #5. I still haven't made the repair just found out about the real cause on thursday after a commpression (dry and wet) test was done. I'm going to pull head myself, the dealer wants $1380 to do it. I can do the mechanical stuff just can't troubleshoot without the damm OBD 2 scanner. I also just had to replace the ring and pinion, carrier, all bearings (only 70,000 on truck). It's alot easier than what you have heard. My first time ever dealing with a rear end and it turned out as close to perfect as you can get.

Same thing with my truck (98 Z-71) both heads were bad so I put in a new engine...

I've had the same thing happen to me with the service engine soon light. it will come on for awhile then shut itself off, and I've been told the exact same thing you were. don't pay to have someone code it until it puts out a strong code. I would suspect this could be an O2 sensor going bad but since there are 4 of them and they go for $50/piece its tuff to replace them w/o knowing which one is bad

You guys that are complaining about being able to scan your vehicle.....I have the answer. I found this site www.obddiagnostics.com This guy designed and built an interface that will run off your laptop (or desktop if you get an extension cable) and will give you output graphs for your O2 sensors and will allow you to pull codes and erase them. It will not allow you to reprogram your computer! You can buy them outright, fully assembled for about $85 from this guy and he does accept paypal. If you go down to your local auto parts store, you can not buy a OBD2 reader for less than $100! This guy even programmed his own software! You can download it for free and try out simulation mode! I am VERY happy with mine. Just check out his site and download the software at least, it works very well with my truck and I was able to find out which of my sensors was triggering a code. You can also use it on Asian vehicles, Fords, and Chryslers, if you own more than just your truck. If you arrive at a code that is not in the program, try www.troublecodes.net And finally, for everyone wondering if your vehicle needs to be reprogrammed, try this OFFICIAL GM SITE http://calid.gm.com and stick in your VIN to see what calibration versions you have in your computer from the factory. It will list updates and TSBs that apply to the update. This will let you know if you need to have your computer reflashed so that it may get rid of troublesome check engine lights. Hope this helps. -Chris

A co-worker of mine is also an ASE certified mechanic and when I had the Check engine soon light come on, he said atmospheric conditions can sometimes make the light come on. He said to pull the negative battery cable off for 5 mins to reset the computer. If the light comes back on you have a sensor problem, in my case it was the O2 sensor on the engine. Auto-Zone does code checks for free! Paid $42 for the sensor (they even had the "special" socket to remove and reinstall! Saved me blig bucks!

What about the stored power the SIR retains after power is disconnected? I have to pump my brakes 50 times after battery is disconnected. Otherwise the VCM memory retains it's info even if left disconnected for 4 hours.

I have seen the check engine light come on and off occasionally on both my gm vehicles. I was told that if you don't tighten your fuel cap properly it can cause the light to come on. Happened on the wife's van and I checked the fuel cap and sure enough it was not tightened properly. Once retightened the light went out after a couple of trips. I think most commonly it is due to an emissions issue. Just my two cents.

Mark