Checking codes???

Is there a way to check the codes on a 91 F-150 without a code reader? Can i use a jumper on the diag port?

Couple ways you can read the codes.. First and easiest is to just jump the test connector as shown and the CEL will flash the codes, or you can use a test light or analog meter and count lamp flashes or needle sweeps..


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Thanks. Is the test connector a single or two wire connector? If two which one do i put jumper too?

The small connector (STI/ Self Test Input) is a single wire.. Use a single wire as shown in red and connect it to the larger diagnostic connector.. The connector is shown as if facing you with the harness out the backside.. Here's a little better test image for clarity.. 


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Cool thanks.