Can diagnostics be made after CEL goes away?

[TomT]

This actually applies to my wife's car. Every now and then the Check Engine Light comes on but then goes off the next day. I'm sure the day I take it into the dealer the light won't be on but can they still find out what caused the light to come on in the first place?

 

[Fred]

Yes, the code should still be stored.

 

[Richard L]

Tom,

No. Once the CEL light condition has been resolved the error code is cleared. There may be a special memory error where it stores some of the last CEL codes, but they will not normally appear on a normal scan gauge when the has been corrected and the CEL has been cleared.



That is how a technician know's the problems have been repaired. Each error that is corrected deletes the corrosponding error code. Sometimes you may get a CEL with multiple error codes and fixing one problem makes all the error codes clear or sometimes just one code clears. It's part of the error detection and correction routines.



...Rich

 

[Kevin Palmer]

I am able to pull past codes with my Snap-On scanner. The info Rich has provided is correct in that once the light is cleared, the specific issue is also clear.



But,,, you can pull past codes which is still useful as it may help you figure out the initial issue..

 

[Richard L]

I guess what Coastiejoe is saying is there is an active error memory as well as an error history memory and the ability to read the history is a function of some scanners.



I had a CEL on my 2001 Sport Trac and took it to the dealer. When they started it, there was no more CEL light and they indicated that no error codes had been stored...so we never knew what caused it and it never happened again.



I thought it might be a loose gas cap and rechecked it. Perhaps that fixed it by the time I got to the dealer?



...Rich

 

[TomT]

As long as the history can be read then maybe they can trace the recurring problem.

 

[Douglas Studdard]

Now on the X-2 I dont believe it shows the these codes but on a Snap on or Ford NGS you can review what is called " Freeze Frame Data" as this shows what occured and what the code is when it was set. This should be in the memory of the PCM for your code. Still, you would have to take into a shop to have them pulled as a simply handheld DTC reader wont show this.



thanks, Doug.

 

[Richard L]

Doug,

Thanks for clearing that up. I did not know the technical name for the Error History log, but Freeze Frame Data sounds good to me.



...Rich