FireMedic1

I own a 2004 F150 Fx4. I turn the key but nothing turns on! The door locks work, lights turn on, even the cig lighter works. I am thinking the problem is the ignition or in the PATS security system. Do the keys/module go bad? I have checked all the normal stuff like the battery and the Alternator.

FireMedic1

UPDATE: Out of the 100+ fuses I found out it was the 20 amp Ignition Switch Fuse that is tripping. Some suggestions on why that would be happening would be great! Thanks

Mod (Ret.)

I have the 2005 Ford wiring schematics manual; I can trace the 20 amp ignition fuse to see whats on that circuit...

My guess (without checking the circuit) would be the starter....perhaps it's drawing over 20 amps to spin. Again, just a guess.

The way I understand it, the key transcoder sends a "go/no go" signal to the PATS system that is located in the PCM (firewall on passenger side). The PCM then allows the coils to fire the plugs, and for the starter to engauge.

If someone does not chime in earlier, I'll check and post for you tonight.

FireMedic1

how would I check the starter for a short?

ford4wd08

if is isnt hard to get off, take the starter into autozone or orielly's they can test it for you

Mod (Ret.)

I'd refrain from pulling a starter just yet.....like I said it's a guess right now until I can view the schematic and see what else is on the 20 amp ignition circuit that could be blowing the fuse. Starters will usually begin to crank slow before they die, and since the poster did not mention this, I'd not suspect it just yet....

Squirtbottle09

I kept tripping that fuse when I installed my cig lighter push button start. I had a exposed wire somewhere and it would blow that fuse randomly. I went through ~5 fuses before I realized what happened. Did you try replacing the fuse to see if it works? There is a trailer harness fuse that is a 30amp in there that you could use temporarrily to see if it works or not.

FireMedic1

Last night I pulled the other 20amp fuse and put it in the Ignition switch feed spot and the instrument panel turned on but when I turned the key to the start position it blew the fuse...... At $5 a pop for this particular fuse I need to get it right the first time!

ford4wd08

yea thats true, you usually can tell when a starter is goin out or shortin out, if you got the book it is best to wait, but for me i can yank a starter off in no time usually so if i was in question and had no other route i would get it tested but i guess thats why we have the forum

Mod (Ret.)

Sorry I'm a day late...here goes:

Two fuses to check: fuse 102 (20Amp) and fuse 101 (30Amp). Fuse 101 is for the battery to starter relay to starter motor. If that's blown, starter gets no "juice".

Fuse 102 supplies 12 volts to ignition switch; when key is in "start" position, voltage is applied to red/light brown to central junction box (fuse box) to dark brown/orange wire. Then to Digital Transmission Range switch (to verify transmission is in neutral or park; located on lower left side of automatic transmission). Voltage from this switch is then connected to Tan/Red wire to starter relay (in fuse box), then to light green/violet wire to powertrain control module (on passenger side firewall; this tells PCM to energize coils (spark)); at same time, the starter relay allows voltage off of fuse 101 to starter motor solinoid via yellow/light blue wire; solinoidd completes path of "direct" battery voltage via a red fusible link wire. Fusible link wires all are off of battery "+" terminal; one goes to starter motor, one goes to alternator, and one goes to central junction box (fuse box).

So, I'd first check fuse 101 and 102, then perhaps the digital transmission range sensor, then any and all wiring inbetween these circuits.