98 F150 Passed Emissions, But Failed Mil/check Engine Light
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Junior Member
Joined: Mar 2008
Posts: 1
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98 F150 Passed Emissions, But Failed Mil/check Engine Light
Took my truck to get smogged today in L.A., CA and I failed the "MIL/Check Engine Light" test. The only further information on the printout is "This vehicle failed the MIL/Check Engine Light Test due to failure to successfully complete all OBD self tests." I changed the alternator last week and disconnected and cleaned the battery terminals. Since then I had only put on about 3 miles prior to inspection. The smog inspector advised me to put the truck through a complete drive cycle of 30-50 miles on both streets and freeways in order to reset the system. He said after that I might pass. However, I'm worried that the problem might be more complex than a simple drive cycle to restart the computer. The check engine light had been on for quite awhile before my alternator failed, but since replacing it and disconnecting/reconnecting the battery the light has gone off. I'd appreciate any help or advice.
-Jared
jlinzmeier@gmail.com
-Jared
jlinzmeier@gmail.com
Senior Member
Joined: Sep 2007
Posts: 500
Likes: 1
From: La Porte, TX
I guess you have both the dyno and CEL tests...
The guy is right. Keep driving and allow the OBD monitors to reset.
How long that takes, or what that all entails, I do not remember.
3 miles definitely does not get things straightened out.
The guy is right. Keep driving and allow the OBD monitors to reset.
How long that takes, or what that all entails, I do not remember.
3 miles definitely does not get things straightened out.
Senior Member
Joined: Oct 2002
Posts: 7,295
Likes: 125
From: St. Louis (Out in the woods)
You have two issues:
1) A pre-existing fault condition that lit the CEL. The alternator repair won't affect that but it did reset the PCM so the CEL was turned off. See torkum's response.
2) Your OBDII readiness monitors had not yet run. The inspector and AlfredB18 are both correct. That is a insufficient amount of driving in order to run the required self-tests so that you can get either a pass or a fail (CEL). Certain test require very specific entry parameters. Most common, you must keep the fuel level between 1/4 and 3/4 of a tank for some of them, especially the EVAP test.. Won't run with either a full or empty tank.
Assuming you drive it and get a CEL, you will need to have it scanned to determine the fault code(s).
Some codes are extraordinarily common. I'd suggest using the SEARCH tool and look for previous discussions regarding your particular DTC. We don't need yet another P0401 or P0171/P0174 discussion, they'd been covered dozens of times. In the unlikely event that there are no relevant discussions regarding whatever DTC you may come up with, then post a new thread in the ENGINES section and seek assistance.
Steve
1) A pre-existing fault condition that lit the CEL. The alternator repair won't affect that but it did reset the PCM so the CEL was turned off. See torkum's response.
2) Your OBDII readiness monitors had not yet run. The inspector and AlfredB18 are both correct. That is a insufficient amount of driving in order to run the required self-tests so that you can get either a pass or a fail (CEL). Certain test require very specific entry parameters. Most common, you must keep the fuel level between 1/4 and 3/4 of a tank for some of them, especially the EVAP test.. Won't run with either a full or empty tank.
Assuming you drive it and get a CEL, you will need to have it scanned to determine the fault code(s).
Some codes are extraordinarily common. I'd suggest using the SEARCH tool and look for previous discussions regarding your particular DTC. We don't need yet another P0401 or P0171/P0174 discussion, they'd been covered dozens of times. In the unlikely event that there are no relevant discussions regarding whatever DTC you may come up with, then post a new thread in the ENGINES section and seek assistance.
Steve
Last edited by projectSHO89; Mar 13, 2008 at 09:14 AM.