Service engine soon.....

[ProEMTPFF]

Ok, my '86 has been running like a champ but today after a 1 hour drive and shutting it off for 30 min., I restarted it. It idled like crap, would stall from time to time. I gave it some throttle and it would studder then rev up fine. The service engine soon light came on but while I held the car at a constant high idle the SES light would go off and it reved fine again but for the most part the light stayed on. I took my paper clip put it in A+B ports to get the code and after the three code 12's the light would just stay solid. Any ideas before I HAVE to take it to the dealership? Thanks in advance.

PS: This is not a new tank of gas, I got it last week and I have ran about half out. No new add on's or mods of any sort in a month now.

 

[Vettefan87]

There is a way to disconnect the ECM without disconnecting the battery. I have always disconnected the battery. That is what I would do to clear the ECM, and leave it unhooked for a couple of minutes then start it back up and see how it runs, then go from there.

 

[vetteboy86]

That is odd, that the engine light did that. I really haven't heard of anything like that. Do you happen to have a service manual. I guess what vettefan suggested would work to clear the code, but you wouldn't be able to find out what it was. However it is something major, it will come back.

Has anyone else had the engine stay on steady, and not flash any codes?


ProEMTPFF, did it ever go back to flashing code 12?


Craig

 

[Ken]

It may be something as simple as a leaking injector. The SES light will go on indicating a overly-rich mixture, but the error code should remain in the memory. I can't explain that one. :confused

Code 12, as you probably already know, is the "everything's okay" code; that the computer's getting a signal.

 

[ProEMTPFF]

It would flash the code 12 like its supposed to 3 times then it just goes solid again. Also, the rad fan is on while the SES light is on. I'm at work today so when I get home tomorrow I'll clear the code "thats not there" and see if it returns and the car runs right.

 

[Hib Halverson]

First, check the engine controls ground. With L98, it's a big bolt near the oil filter. It has a lot of black wires connecting to it. Remove the bolt, clean it and all the connectors then reinstall the bolt.

Clear codes and road test. If the code persists, you need to get the ECM memory when the code is present. You may have better luck with a scan tester.

I'd also get yourself the 86 Service Manual as that has the instructions on how to solve the code.

 

[vigman]

ECM failures

The drive transistor which does the actual blinking of the light sometimes fails..
( I've personally had 2 go out) The TYPICAL failure is the light is STUCK ON.

It is ODD that it would blink 12 .. 3X and stay STUCK ON... one of two possible answers here....

1) The ECM hangs( stops communication) and stays latched up, leaving the SES light on.

2) The drive transistor is dying and shorting out .. but I would think that as it's blinking.. the light would not go all the way out.. and start a bright / dim sequence...

I'm a little puzzled by this as well...

Get a hand scanner.. that takes the light bulb out of the loop and the ECM puts out serial data ( down a different line ).. and that might shed some light on things.

The radaitor fan will come on while polling for diagonstics.

Good luck

Vig~

 

[ProEMTPFF]

Ok, I cleared the code, fired her up and went for a test drive....everything fine YESTERDAY. Today, fired her up and the SES light came on "car running fine" so I broke out the the tester and it showed me a code 43. One book says a code 43 is the knock sensor and the book for the code tester says to check the electronic spark sensor for low voltage.

 

[Hib Halverson]

If you're using a non-GM publication for service data, most of them are marginal in their usefulness to troubleshooting engine controls problems. In those books "knock sensor" (the correct term) and "electronic spark sensor" might be the same issue.

A book that says the problem is the knock sensor but gives no other troubleshooting or diagnostic info is useless.

In many cases, to properly troubleshoot a fault code, you need the factory service manual.

On the other hand, if the book that said DTC43 is a KS problem gives you some additional diagnostic or troubleshooting info, I'd use that data rather than the info. in the code tester book, to help you.

 

[garylt]

I have a 1986, service engine soon light comes on, but not all the time. What does this mean.

 

[Vettefan87]

Mine did that, and it was some EGR code that the shop didn't clear or something, I can't really remember. First I would check the codes. You can do this with using a paper clip and shorting out the first two ports I think on the diagnostic port. Then turn your key to the on position and your primary fan should come on, then your SES light will start to blink. I think it blinks twelve times, then it will blink however many times the code is then all you do is look up which code it blinked. You might want to start a new thread once you check the codes. Good luck.

 

[vetteboy86]

The way it blinks is like this:

One blink then off
Two blinks then off

One blink then off
Two blinks then off

One blink then off
Two blinks then off

Each will have a short period between them. Two blinks will occur one right after the other, you have to see it to know.

Then after the series of three 1 and 2, which is twelve, which means you are ready to communicate, it will flash the code, in the same manner as the 1's and 2's.