View Full Version : Weird Check Engine Light

11-29-2006, 09:17 AM
Can you hook up an OBD reader while the engine is running?

My car will not "throw" codes.

My check engine light won't come on while my car is idling. I have to drive it a couple of miles before it comes on. Therefore when I shut it off the CEL goes out and I can't test it.

Any ideas????????


PS: the car does have a rough idle with or without the CEL on.

11-29-2006, 09:27 AM
You're probably already doing this, but I'm just checking... When you hook up your scanner to the trapezoid-like connector, are you also connecting the single loose connector to it? It needs that one as well to read the codes.

11-29-2006, 03:43 PM
Yes the single line is being connected as well.
What my question is:

Can the code scanner be hooked up while the car is running?


11-29-2006, 03:51 PM
It should be able to be hooked up and then driven. Kind of sounds like an egr problem.

11-29-2006, 03:52 PM
i doubt it but if your check engine light is coming on. that the code should be saved in the ecm for like 50 starts i think or a battery disconnet.

11-30-2006, 09:40 AM
i doubt it but if your check engine light is coming on. that the code should be saved in the ecm for like 50 starts i think or a battery disconnet.

Now that's what I thought.
But when the tech hooks up the code reader the only codes he gets is:
(i think)

He told me yesterday that the car had to be shut off to hook up the hand held reader.

11-30-2006, 09:49 AM
go to your closest auto zone they will do free scans and they wont say it your car if they dont know what they are doing ;) .

11-30-2006, 09:52 AM
Also when the light comes on dose the car run bad or anything. Some times my light has came on befor. I never found the problem maybe a sensor just out of limits and it thros the light on im not for sure .

lots of people on here say if its not broken dont if it. well if your car is running good maybe somthings not broken.:rolleyes:

11-30-2006, 06:00 PM
I like that philosophy too. "If it aint broke don't fix it"

But........The eninge has a stumble in it. You can't feel it when your driving. When it is idling it is VERY obvious because the whole car shakes.

So I'd like to get that fixed.

Then if its still on then I'll just pull the bulb out.

11-30-2006, 06:36 PM
Hook up the tester, then drive it, then run the test when the light comes on.

Scott Long
11-30-2006, 11:38 PM
It can test KOEO and KOER. Which in laymans terms is Key On Engine Off, and Key On Engine Running. I've never driven around with it plugged in since it hooks under the hood and I couldn't read it. But you could technically do it and then count the flashes of the light if it comes on. It should store the code in memory though.

I have a code reader in the glove box of each of my SC's. Just the little Actron hand held reader but I know how to use them and they work fine for me. Just as good as the Snap On reader we have at work that has a display and reads out the codes. Just a lot cheaper.

You need to let it test for a while. It goes through and repeats itself and then moves on. So if it says 1 1 1 and then 1 1 1 and then 1 1 1 and the guy stops, he is only getting the first memory cell of the KOEO test. It will repeat so you have a chance to get all the codes.

Say you have code 152 and 238. It will go through and flash and beep 1, 5, 2 pause..... 2, 3, 8 pause..... 1, 5, 2, pause... 2, 3, 8, pause, 1, 5, 2, pause, 2, 3, 8, pause, beep, pause.... then move on to the next memory bank. It will go on for a few minutes so make sure the guy isn't rushing you when it's being tested.

Auto Zone here couldn't test it when my girlfriend brought our other SC in. The guy had no clue. He knew the Chevy OBD1 with Key, and the OBD2 handheld reader, but had no clue with the Ford EEC IV computer. I used to be the only guy who could do Fords when I worked at AZ and people used to send customers to my store to let me look at the fords.

So make sure the guy knows what he's doing and not just plugging it in and telling you it's fine.

12-01-2006, 09:25 AM

Thanks for the information brids4us and Scott. I'll guess I need to get my own tester. I think I saw them on ebay for pretty cheap. The guy didn't really rush me at AZ i know that the code repeated several times. But I'm not sure if he let it run long enough.