Service Engine Soon Light

[ReggieD]

1992 LT1
How do I diagnose the reason my "Service Engine Soon" light comes on erratically. I drive on the highway for about 20 to 30 minutes then the light comes on. After about 20 minutes the light goes back out. This activity is very erratic. What can I do to figure out the problem?


I know this light is linked to fuel, ignition, and emission controls. How can I narrow it down?

 

[rrhayden]

You need to determine what code is being set. You can do it with a paperclip across 2 terminals of the adl connector. I dont want to give you the wrong info, I THINK it is a&b. Do a search here and there is a drawing and a detailed explination. I bet it is a code 32, mine does the same thing.

 

[vette-dude]

My 91 L98 does the same thing if I don't allow it to warm all the way up before driving it. Once the SES light comes on it will go out after awhile or if I stop and restart the car it will stay off as long as I am driving. It is a Code 32 which is the EGR system. Can't find anything wrong with the EGR Valve or any other part of the EGR system. I suspect what happens is that the car when cold is in an open loop and when the thermostat and engine reach proper temp the car goes into closed loop and the cooler air going in to the TB is picked up by the MAP sensor and trips the SES light. Maybe this is why GM put a MAF (sp) device with the heated grid screen into the newer models air intake. I just drove the vette to Philly and it got 27.4 MPG and ran flawlessly so I am just going to ignore the SES light for now. (Car was tuned up less than 100 miles before this trip with new plugs, wires, cap, rotor, O2 sensor, fuel filter, and air cleaner.) If anyone has an answer to your problem I would like to hear how you fix this.


Randy

 

[Hrtbeat1]

Check the EGR tube that runs down to the catylitic converter. When I bought my car mine was disconnected (jury rigged ... folded over and brazed closed) and I would occasionally get the code 32. Not all the time ... which I thought was strange. To fix my situation I burned a new chip and turned the EGR off. Simple fix.

 

[vette-dude]

Check the EGR tube that runs down to the catylitic converter. When I bought my car mine was disconnected (jury rigged ... folded over and brazed closed) and I would occasionally get the code 32. Not all the time ... which I thought was strange. To fix my situation I burned a new chip and turned the EGR off. Simple fix.

How do you burn a new chip?? Or who can do this?? Thanks.

Randy:W

 

[Hrtbeat1]

There are a few of us around that can burn a new chip. It takes having the equipment (my burner is a pc board), a chip, and a starting point (the stock .bin file ... the actual program on the chip.)

 

[vette-dude]

I am interested. Any idea how much it would cost? I will check the air line to the CAT tonight and see if it is corroded or not hooked up. I think it is probably ok but that is one thing I haven't checked. I think the Computer has been changed at one time or another. Would I just remove the old chip and send to the new chip maker so they can get all the needed info to put on the new chip? (I think that's what you meant.) Thanks.

Randy

 

[Robertwav1]

Maybe somebody has the website but, they talk about the chip for the vette and it says it's really no good unless a computer is hooked up to your car and info is taken on exactly what the car is doing under different loads. Only then can the chip be programmed to get what you pay for. If the site is not listed by someone I'll look it up at home and repost. I believe the only thing a generic chip is good for is to not let OD come on til 50 some MPH instead of the 47 or 48 MPH. Secondary fan temp is changed also. You really need to take a history on the cars performance first from what I've read, only then can adjustments be made. All mods should be completed before an EPROM write.

 

[WhalePirot]

All that is quite true for a modified engine, but the first order of business here is to pull the code and then troubleshoot. Seems we are headed down a path which may or may not remedy the problem.

 

[Hrtbeat1]

Seems we are headed down a path which may or may not remedy the problem.

So right you are. I kinda jumped the gun a bit there. This was the easiest and cheapest fix for my particular situation, as I would have had to replace the whole exhaust (CAT was removed and a Y was welded in its place). I had already replaced both the EGR valve and the solenoid, but it wasn't until I was under the car that I found the real culprit to my problem.

 

[ReggieD]

Code 26 and code 32

Here are the two code numbers I received for my 92 vette.
Code 26
Code 32

What do you all think should be my next step?
Can I still drive the car?

 

[vette-dude]

ReggieD -- Did you ever get the problem solved and how if you did??? Mine is still giving me fits with the Code 32 thing. Waiting on some answers from the CAC group. Am going to look for vacuum leaks tonight. Then I am stumped!! (Sorry for the hijack but it looks like we are trying to fix the same problem.)



GMjunkie -- If you weren't so far south and west I would bring it down and let you perform an exorcism on my 91. Gotta get this fixed.


HrtBt1 -- Going to try and find cause of SES light and code 32 befroe I think about burning a new chip.

Randy:confused

 

[JonM]

I would start with code 32 Barmectric pressure( BARO) sensor circuit failure or Exhaust gas recirculation (EGR) valve diagnostic switch-closed during engine start-up or open when EGRflow requested by ECM or EGR/EVRV. Code 26 may be related Quad-Driver module or Quad-Driver No. 1 error. :eek Call me at 1-877-677-2984 Toll Free ext. 1 or2 ask for Jesse I can Talk Way better than I can Type!! I am here most of time!! gmjunkie!!

Can we all phone you and can we do it anytime?

 

[Rogue]

When my "Service Engine Soon" light came on, it was the knock sensor that needed to be replaced. Problem solved.

 

[Robertwav1]

When my "Service Engine Soon" light came on, it was the knock sensor that needed to be replaced. Problem solved.

Must be somthin' with the blue color...It's the only sensor I've ever replaced in my car "The knock sensor".

Another possible problem with knock sensors is mis-triggering on some other vibration. One example where this is common is on modified cars with aftermarket headers. Space is usually pretty tight, and a header tube might rattle against another part under acceleration, or a manifold bolt might work loose. These subtle problems can drive knock sensors nuts. You might also see some knock sensor activity on a badly worn engine from a noisy valve train or worn bearings. Odds are good on those engines that the few degrees of lost timing advance isn't the biggest issue to worry about!

 

[Blue89]

Here's another Blue one with the service engine light on........what is a "knock sensor" and where the heck is it??

 

[I_R_DA_ONE]

Here's another Blue one with the service engine light on........what is a "knock sensor" and where the heck is it??

Your knock sensor is on the pass. side just in front of the starter on the engine block... The knock sensor is for telling you that the grade of gas you are running is to low or your timing is to high.... this prevents you from harming your engine due to spark knock...
Mike R

 

[Blue89]

Thanks for the post! I'm using the best gas "Speedway" has to offer, maybe it's time to change brands..

 

[I_R_DA_ONE]

If you are using good gas you might want to have your timming checked...it might be set to high..
Mike R

 

[Robertwav1]

Here's another Blue one with the service engine light on........what is a "knock sensor" and where the heck is it??

A couple sentences on just what "knock" is. In your engine, the fuel mixture is injected, and then the piston begins its compression stroke. Somewhere just before the piston reaches the top of its travel, the spark plug fires, igniting the mixture. That's actually a pretty well-controlled burn and it creates the pressure needed to drive the piston down through its power stroke. "Knock", also called pinging, occurs when something causes the fuel to ignite in an uncontrolled manner, usually before the spark plug even fires. This is a violent event in the engine - heavy pinging can lead to all kinds of internal engine damage.

Remember the cars of the late 70's and early 80's? It sure wasn't unusual to here them knock. But in today's vehicles you (almost) never hear as much as the slightest knock. Improved electronic controls play a big part in that, but the unseen hero is our friend the knock sensor. This little guy detects vibration - but much more than that, it can actually tell the difference between the engine's normal shakes and rattles and knock. Pretty impressive considering all the mechanical motion going on in an engine.