1990 F 250 Engine Compartment KOEO Self Test Input Connector
20

Asked by GuruB83DD Jan 13, 2019 at 12:19 PM about the 1990 Ford F-250 2 Dr STD Standard Cab LB

Question type: Maintenance & Repair

In order to perform Key On Engine Off test, to get trouble codes at dash, I try
the Signal Return Test as shown in most manuals. Check engine lite,
routinely comes on and off while underway. (trying to find cause of hard start,
then solid, good run for up to 50 miles and then, time to time, 'run out of gas',
while, for example, idling at a stop) Signal pin pig tail does not work, with no
resulting code flashing when key turned to on. Worked well in the past,
flashing codes with no trouble. Manuals give no info regarding how to find
the cause of the failure of the actual Self Test Connector itself. How, exactly
do you find the cause of the Test Connector failure? Obviously, i'd be one
grateful guy to get any idea how to go about that. Thanks for any reply.

4 Answers
42,870

Hornet_2497 answered 5 years ago

This OBD port is fused and I am told it is fuse #3, the same as the cigarette lighter fuse. This would probably be in the fuse block in the passenger compartment. Some say it's 10 amp but cigarette lighters are usually fused 20 amp. Or you can just check every fuse one at a time to find the burnt one. Your truck being a pre-1996 vehicle will be OBD one not OBD two. Call around to see if some auto parts store can scan that for you. My reply is based on several bits of info so it may not be correct but try anyway. Good Luck.

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GuruB83DD answered 5 years ago

First thanks for the reply and interest. Fuses in passenger compartment are good, though I did not check the engine compartment fuses,a possibility I guess. Except the 'check engine light' comes on and off as it should. But you give me the idea of checking lines at the ashtray,cigarette lighter. I will definitely report back. Thanks again.

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GuruB83DD answered 5 years ago

Okay, thanks, one previously unnoticed wire, loose, at Pigtail. Works well now, for reading codes, many 63 and 21, so replacing Throttle Body Sensor. Thanks for your input again.

1 people found this helpful.
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