I have a 96 F150 I took it to get smoged the other day as my registration is up they hooked it up ran the test and came back and said I failed. Actually they said everything passed but I failed because my check engine light didn't come on it hasn't worked for some time I just forgot about it. I went and got new bulbs changed the two that say CAV 3 below them on the black housing and when I turn the key to the on position it still doesn't light up everything else lights up so I am stumped. I swapped the one from where it says ABS and still nothing. I am not a master mechanic, nor an electrician so if anybody might be able to give me some kind of an idea I would greatly appreciate it.

Thank you,
Bob.

 

Anyone would be stumped! Verify that the damn light goes on in it's socket in the gauge panel, by applying battery + to the wire feeding the lamp, in the harness. You may need a wiring diagram to determine the correct wire in the bundle feeding the gauge panel, though, if you can't figure it out. It's likely a printed circuit feeds all the lamps, so difficult to tell which wire, but it can be done. If the lamp lights during this test, it will be necessary to run continuity check all the way back through the computer plug; if it does NOT light, the trouble obviously lies between your break-in on the wire, and the lamp socket. Could be the plug-in of the harnness to the panel, or the lamp socket itself.

A bad connection anywhere between your test point under the dash, and the computer plug, could cause failure of the lamp to light. You will need the "pin-out" diagram for the computer plug.

If continuity checks out, the possibility then would be suspected of the computer being at fault. (though unlikely).

One other funky test before any others: disconnect a sensor which still allows the engine to keep running, and see if the "Check Engine" light illuminates then. The EGR Valve Position sensor should do this if unplugged. Sometimes called "EVP" sensor. If that light illuminates under those conditions, you can forget about bad connections and ALL the continuity tests. Try a known good computer in place of yours.

Good luck! Let us know results. impish

 

You do not put power on a wire to test it.
The computer grounds the MIL to turn it on.
It is not called a Check Engine Light (CEL).
It is call a Malfunction Indicator Lamp (MIL) on a 1996 Ford Truck.


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