1989 Service Engine Soon lamp issue

[77Impala]

On my 1989 GMC C1500 the Service Engine Soon lamp has been lighting up now and then for the last 2 days. But it does not stay on and this morning I used my scan tool to look for codes before starting up, it found none. Left the scanner plugged in and when I got to work the SES lamp lite up so I ran my scanner again, and sadly it said that there were no codes, yet the SES was on. Tried a second time with same result. So I parked the truck and before I turned off the engine the SES lamp had turned it self off again.

Has anyone ran into this issue and found a way to get the code from the ECM?

 

[Lordkay972]

I had the same problem. Also couldn't get a code. After I replaced the o2 sensor the light hasn't came on again.

 

[77Impala]

Thank you.

Went ahead and replaced the 02 sensor. Not only is the light not coming back on but the truck is running smoother and quieter now as well. Maybe I might get a few more miles per gallon.

 

[jmc1997ck]

O2 sensors seem to be the culprit. Same deal here. Light came on and off several times over the course of a few months. No codes thrown. Replaced sensors, back to normal. For... Now...

 

[twomanymontes]

I had the same problem. I changed out the sensor only because the crossover pipe rotted. I put a new one in and the light hasn't been on since.

 

[77Impala]

Still getting the Service Engine Soon light coming on and going off randomly. And still cannot get any codes from the ECM. Even with the lamp lite the message is 'No stored codes' and the green healthy LED is lite up on my scan tool. I am just going to ignore it for now. Maybe later it will have a reason to be lighting up much more steady and give me a code then.

 

[77Impala]

Not getting the light for about a week now. Seems the problem has to do with my air pump. The hose for the pump was not hooked up to my air cleaner housing so I bought the little fiberfill filter and reattached the air pump hose. Over the last month I noticed that the fiber filter kept blowing out of its little housing. Last week I decided to remove the hose and point it towards the fender as it had been before. Since then no SES lamp.

Now need to figure out why the air pump is not pumping correctly, or just remove the thing since a GM tech told me years ago that after 20K or so the system did not work as designed anyway.