I have a 2002 ford ranger with the 3.0l 2wd. I just started my truck and was sitting in in (truck is in park) waiting for the engine to get warm when all of a sudden the engine shuts off.

I checked the voltage on the battery and it was reading 12.25V and even tried jumping it with no success, not turning over or clicking at all. I realized I wasn't hearing my fuel pump either so I switched my PCM relay and my blower relay and it started up and ran fine.

No fuses are blown or anything so what could have caused that single relay to blow without effecting the fuse or the surrounding relays?

 

PCM relay sends power to the PCM(computer), of course, but also the fuel injectors and Fuel Pump Relay.

2002 Ranger also has PATS with starter relay interrupt, so no PCM power means no PATS key test so no starter motor.

Ignition switch under the steering column Turns ON the PCM relay, does Key switch on steering column feel loose at all?
The key switch, when turned, pushes and pulls on a rod that runs down to the ignition switch and slides it into its various positions, ACC, OFF, RUN, START
If loose the connection can be lost as ignition switch slides out of position.


But yes, it is unlikely for a Relay to fail while it is on, it is just a coil of wire around a metal core that turns into a magnet when power is passed thru it, that pulls down the Contact Arm to pass power to system.
So not alot that can go wrong.
But they can fail, like any moving part, so I guess just keep an eye out.


FYI, 12.2volts at battery, key off, means it can only hold 50% charge so is probably 5 to 6 years old now
I would shop for battery sale sooner than later
A very cold morning could get you the dreaded "click, click, click"

New battery is 12.8+ volts
3 years old about 12.5 volts
Measured after sitting for over 4 hours
Batteries use chemicals to store a charge, these chemicals get used up over the years, so batteries wear out