Contour Enthusiasts Group Archives Forums General Troubleshooting CEL turned itself off? (Kinda long)

Short history:

Car is a 98 SE duratec ATX w/ 77K.

About 4 weeks ago got a CEL after a moment of full throttle acceleration. Thought maybe the computer just confused, so disconnected the battery to reboot the computer and see if it would happen again.

1 week later, happened again after another full throttle run. This time I took it to AutoZone to have them read the code. Came back that precat in bank 1 not at proper efficiency. He clears the CEL.

Next day, it happens again. So I go to the Ford dealer to ask about the emissions warranty. Service tech says if it's the cat they will replace it, anything else I have to pay for it. They will charge me $80 to diagnose it. If it's it the cat, the diagnosis is free. So I figure I will think about, maybe change the oxy sensors this week-end and see what that does (they're about due anyway..)

Then I notice that the CEL is off when I get in the car yesterday. I didn't know they would turn themselves off. Does the computer turn the CEL off if the problem doesn't show itself for a period of time? I did a few full throttle runs since then to see if I could trigger the CEl again. No CEL. I suppose this is good news, but I am just wondering about it.

The car seems to be running fine, except that after the second CEL the car seemed to stumble when the "secondaries" opened. It didn't lose power altogther, more like it was surging from having trouble getting a good mixture. It only did this once. (Though I have noticed it in the past. I don't go full throttle very often because I still have the original WP and have noticed that many people's WP failure occured after a full throttle run.)

Any insight would be helpful

Thank you,

Richard

Yes the CEL can turn itself off. The system rechecks for certain conditions every time the car is started and the system has enough time to run through a series of 'tests' or checks on performance. If the original problem that set a code is gone for a number of complete system checks, the code will drop out, and the CEL will go off.

What was the code number? It would be of the format Pxxxx. Also, did the code show up in the KOEO or KOER tests, or was it in continuous memory only?

Some diagnostic trouble codes (DTC's) clear themselves under certain circumstances. In particular, if you go through the same set of conditions (engine RPM, % load, temperature, maybe others) that were in effect at the time the DTC was thrown, but the PCM doesn't sense the malfunction anymore, the code may be cleared with the reasoning "guess it was a glitch last time."

Unless the CEL is a HARD CODE, meaning you have a sensor fault, like a faulty Mass Air Flow, or bad O2 sensor, the CEL will turn itself off after 3 or 4 starts.
With a Hard Code, the light stays on until you reset the PCM.

Pete...

Thanks for the replies.

Does the computer store the code for future reference (presuming the battery stays connected) even if the CEL is turned off?

Richard

No. For the Catalyst Efficiency Monitor, the code is erased if the malfunction is not detected during three sequential driving cycles.

If you're only getting a cat efficiency code, I'd say pay them the $80 and see if they'll replace it. Besides, you could just be wasting that $80 by needlessly replacing the O2s first. I'd go with the repair that may be reimbursible first.

Tell that to my moody car!

Thanks all for the input

Richard

mine has turned itself off P1131 (HEGO sensor), did it again this week!

this is 2x now... every time i goto call the garage to have the O2 sensor changed, the CEL goes out! i guess my Contour doesn't like it's pants down

I had P1131 turning my CEL on and off for 3 months before finally changing out the sensor (once I finally got a cheater bar that fit over my ratchet handle). 3 weeks and 800 miles later, no CEL, and I'll tentatively say my fuel economy is back up to where I'd expect it to be in the Fall.

Toadster, if all you have going on is P1131, I say pull the trigger and swap that sensor! With the How-To's scattered about this Forum, you could even do it yourself as a bonding experience with your car!