Failing to turn over, sound coming from fuse box.

I have a 2003 Expedition XLT that has recently had an issue starting.

About 2 weeks ago it would not like to start easy in the mornings and at other random times. When it died in the driveway I had the front and rear fans on 4 and tried to start it. Instead I got a loud buzzing noise coming from the fuse box. I tried to connect my code reader to it but it just said failed to connect. My instrument panel has power but the odometer reads - - - - - -. I had the battery tested and subsequently replaced it. After replacement the buzzing from the fuse box lasted about 10 seconds and once it stopped I could start it again. At that time the code reader was able to connect. The next morning it briefly did the buzzing thing but once I turned the fans off it stopped buzzing and I could start it. I have no problems with it until two days ago.

I went to start it, had the fans on 4 again, and instead of starting I just got the loud buzzing sound. The battery voltage read about 12.35 volts so I hooked a battery charger up to it. After two hours the battery is reading 12.87 volts at the terminals. The PCM fuses 32, 33, and 34 read about 6 volts. All the small fuses read about 12.6 volts and the applicable larger fuses passed a continuity test. Now I just get a short buzzing sound then it turns into a steady repetitive click. Still no odometer and code reader cannot connect.



Any suggestions would be greatly appreciated.

Anytime a relay buzzes the usual cause is low voltage to it.
Perform a voltage drop test between the + battery post and the + post to the fuse box. Perform the same test on the negative side of the circuit. Negative post to chassis ground. Max reading for both sides is .5v dc. A higher reading indicates a resistive circuit between the leads being tested.

I have not done a voltage drop test before, done it sound like I am doing this right?

The battery voltage is now at 12.46 volts. I located the plug that powered the buzzing relay. I hooked the positive lead on my meter to the positive battery post and the negative lead to the wires that supplied power. Of the ones that supplied power they read 12.45 volts.

For the negative side I am a little confused and think I am doing it wrong, negative post to the ground is 0.00 volts. Hooking the positive lead to the negative post and the negative lead to the wires all read 0.00 volts.

I'm using my phone so the replies will be short. Check youtube for doing the voltage drop testing, watch "Eric the car guy" if he has one. No bs - right to the point.

Thanks for the help, it was the PCM Relay. Being the PCM voltage readings were around 6v when I was doing my fuse check I thought that I might as well swap it out with my spare relay and it fired right up.