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bwcall 07-03-2008 01:09 PM

Fuse 18 Keeps Blowing
I had my CEL on for a week or so, got it checked at AutoZone, it was the code that shows O2 Sensor 1 as malfunctioning. So I go ahead and order a new O2 sensor, but in the meantime I'm reading up a little bit and read about checking Fuse 18; it was blown.

So I replaced the 10A fuse with a 25A fuse (all I could find spur of the moment), and that fuse blew too after about 2 miles of driving.

I do some more reading and people suggest it might be a problem with the ECU. I guess it's time to get that checked. Is there some kind of warranty covering the ECUs? 8/80,000 correct?

I guess my questions are, is it worth taking to get the ECU looked at? Could it be something else? Should I check all my O2 sensors and make sure they are Ford Motorcraft brand before I take it into the dealership?

focusguy87 07-03-2008 02:28 PM

You could hook up a meter and see what its doing exactly. Guess ford would do that anyway.

BlueFocusSVT04 07-03-2008 04:47 PM

Take it in for service to an authorized Ford SVT dealer. They will probably charge a lot, but they will help you.

InfraRedSVTF 07-03-2008 05:21 PM

Most likely the heater circuit in the o2 sensor shorted out. Get a new o2, and replace the fuse with one of the proper rating.

pat247 07-03-2008 05:45 PM

First thing I would do is a visual inspection of the wires under the car that plug into the O2 sensor. Look for damaged or burnt spots, if the wires look good then replace the O2 sensor and if the 10A fuse still blows then take it to an authorised dealer.

Grich171 07-04-2008 12:26 PM

if you have a high flow cat or no cat that could throw a CEL on...i would try and get a wiring diagram of the circuit with that fuse in it and see whats goin on and check the wires

RecoilRob 07-04-2008 12:40 PM

The forward O2 sensor is really close to the tranny and it doesn't take much of a hit on the pipe to jam it with resulting damage.

More than likely, it has hit and hurt the wiring on the sensor. Replacement will cure it but make sure the pipe is down where it belongs so the new one won't get ganked.

bwcall 07-04-2008 02:47 PM

I replaced the front sensor (it was a Bosch) with a Motorcraft part today, and the fuse still blows after turning the car off and back on once (still drives fine, however). So I guess it's off to the dealership.

nickl16 07-04-2008 10:36 PM

your back one is probably dead as well, both of mine went at the same time and were causing the fuse to blow

Telly 10-01-2012 07:13 PM

Did you ever find the problem? I'having the same problem, F18 blowing as soon as I turn on the key, with the O2 unplugged. I'm getting 4 ohms on the terminal coming out of the fuse panel. The wire looks like it runs back into the cab before coming back out to the O2 heater.

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