My service engine soon light periodically turns on and about 75% of the time, it comes on when going slow up a long hill behind someone slow. I posted this a few weeks ago and everyone said to test it with a code reader but when i do that, it reads nothing because the code only comes up every once and a while.

So i was wondering if it is okay to plug the code reader in, when the light comes on, while the engine is running. If i shut the engine off, the light will go off and the code will disappear.
Even if i shut the engine off while the light is on, then restart the car..the light will not be on.

 

Be honest. Do you properly know how to retrive codes that are stored in the ECM?

Tell me what you are doing, and Ill try to help you out.

BTW where in Pa are you from?.....Tom

 

Code should be stored in the ECM. Check here, it'll tell you how to retieve it on your own. Scroll almost to the very bottom.

 

I have a plug-in GM code reader from an Auto Parts store, basically a shorting bridge in a plastic handle that plugs into the port. The instructions start out by saying, turn off the key, plug in the reader, turn on the key, count the flashes.

The check engine light comes on while driving and stays on until the key is shut off. Once restarted, the check engine light is no longer on, and the ECM reads no codes using the above method. I was just concerned that if I plug the reader into the port while the engine is running, we might whack something in the ECM.

My first thougt was that the CO2 sensor was going bad and the slow hard pull was causing the sensor to read out of range somehow. Another theory that the converter may be going out, but my experience in the past when a converter was failing was that you have a marked loss of power as well.

BTW: 15 miles south of Pittsburgh

 

NO, you can run the engine with it in. Thats how you can tell if its in open or closed loop. But dont do this for your problems.

Are you getting a code 12? By that I mean, 1 blink, pause, 2 blinks?

After you say you have counted the flashes, you talk about the C/E light coming on while driving, and staying on until the key is turned off. I believe you are not finding the troublecodes.

When this happens, a code is being stored, and it is alerting you of it.

Jump the ALDL, and turn the key one click, and observe the C/E light. A code 12 will blink, showing the system is operating properly. You should not be driving, but parked.

You have to verify a code 12 3x, and then each code, or additional codes will flash,(write them down)also 3x.

When the code 12 flashes at the end you are done retrieving the troublecodes.

Then its time to get a manual and see what codes are what, and work at getting the problem fixed. Keep me posted...Tom Oh, Im in the Scranton area.

 

If the code is disappreaing when you turn it off, make sure you have a stock (not Hypercrap) prom. I saw this kind of thing last year, was my EGR.

 

Almost sounds like you're restarting the engine, you don't want to do that. Just turn it one click to on and the light should flash.