CEL keeps going on and off
Thread Starter
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Junior User
Joined: Jun 2004
Posts: 66
Likes: 1
From: Big Rapids, MI
CEL keeps going on and off
The Check Engine Light on our '96 Explorer has been going on, then off, then back on, then back off, etc. for the past month or so. I took it to AutoZone a week or two ago and they pulled the code - I forget the code number, I think it was P0421 or something, but the message was "Catalyst System Efficiency below threshold (bank 1)".
I was under the impression that once the CEL came on, it wouldn't go off until the code was deleted or the battery was disconnected for 15 minutes. So I'm a little confused why the light keeps going on and off. Is this normal? Will this code cause the light to be on sometimes and off sometimes? Or is something else going on?
Thanks!
I was under the impression that once the CEL came on, it wouldn't go off until the code was deleted or the battery was disconnected for 15 minutes. So I'm a little confused why the light keeps going on and off. Is this normal? Will this code cause the light to be on sometimes and off sometimes? Or is something else going on?
Thanks!
Senior User
Joined: Nov 2003
Posts: 163
Likes: 0
From: Bucks County, PA
Depending on the code the CEL will turn off when the fault no longer is present or after a certain nomber of start-ups with no fault present. Hopefully your problem is related to a weak O2 sensor after the catalytic converter and not a bad cat. Good luck.
Junior User
Joined: Dec 2004
Posts: 73
Likes: 0
I had the same problem in my "new" 94 Explorer. I could feel a slight hesitation or loss of power before the light would come on. It would stay on for about 10 seconds, go off for about 10 seconds and so on. I poured a bottle of STP fuel system cleaner into the gas tank and the problem went away immediately. NO more hesitation and no more CEL. Hope your fix is as simple and cheap as this! Good luck.
