The other night the Ford F150 left us stranded.

On the way to the local Johnny Rockets we hit some heavy rain. Some of the puddles on the right side of the road were rather deep and I found myself quite glad for the new tires we put on some months back. They cut right through but sent water flying everywhere. The truck didn’t miss a beat. We lucked out and parked right in front of the eatery, and went inside to consume heart attack inducing burgers washed down with some of the best milkshakes on Earth.

Satiated, we left the restaurant and climbed into the truck. I knew something was wrong the instant the key moved through the positions, the usual sounds and bongs were… well, they were different.

The mini message center displayed a cryptic message: Check Gauges in that odd font that LCDs use when making text from a limited set of segments. No starter crank at all. Instead, only an audible click coming from the fuse box under the passenger side kick-panel.

Hoping to avoid a call to Triple-A I dialed some friends to beg a ride (thanks Randy & Rose!), intending to leave the truck where it sat and troubleshoot in the morning. I felt pretty strongly that the problem was moisture-related – that was an awful lot of water! Maybe it would dry out overnight.

Around noon the following day I returned. The truck started as though nothing happened. I listened for a few minutes – nothing odd – turned it off and went home to get Pam to drive the thing home.

The round trip took about an hour. Pam jammed the key in and… yup, no crank! I got behind the wheel and gave the key a few disgusted twists. Wonder of wonder it fired and settled into a welcome idle. Pam drove it home without incident. But in the driveway it wouldn’t start again until the problem was found and solved.

When it comes to auto (and motorcycle) repairs there’s nothing in the world like the actual factory shop manuals. I have ’em for all our vehicles – except this truck. That’s because you can’t simply buy the shop manual for the F150. About the best you can do without springing for an expensive subscription to the online manual – like a dealer has – is to rent access to a section for a day. And that really sucks! So when things go wrong this truck either goes to the dealer or I use the Internet to learn from those before me.

The first likely candidate for failure seemed to be the Fuel Pump Driver Module (FPDM). This aluminum and plastic box, which regulates fuel pressure by modulating the voltage pulses sent to the fuel pump, is mounted directly to a steel crossmember under the bed, above the spare tire. The dissimilar metals tend to corrode the FPDM’s case, eventually allowing water to harm the circuitry inside. Water. I dropped the spare and unbolted the module, disconnected the single plug and brought it to the bench. The metal case was plenty corroded but intact. I didn’t open the plastic cover. Back onto the truck it went, with no change in symptoms. I never learned whether FPDM failure would cause a no-crank condition, or simply a no-start condition.

I entered the truck’s test mode and scrolled through the displays in mini message center. I found DTCs D900 and D950, but searching online for those codes brought no insight. It seemed like there was fuel pressure, consistent with an undamaged FPDM. There was lots of other stuff in the displays but much was undecipherable.

I figured it was time to add a new tool to my collection: a reader to plug into the truck’s diagnostic port. I grabbed one of the bikes and took a ride down to the local parts store, the nearest was Advance Auto Parts. I intended to just get a simple reader but ended up going a little more spendy for a unit that promised to talk to my Android phone and deliver more comprehensive information. The device I bought is called U-Scan by Actron, model number CP9599.

I had problems with the CP9599. It didn’t seem to want to talk to my truck – but it had no trouble at all talking to my Jeep. This proved to be an important clue. Instead of just some random failure, now the trouble seemed like something was awry with the PCM. Maybe it had taken on some water? Maybe communications, maybe power, hmmm.

I pulled and inspected the condition of all the under-hood accessible plugs I could find, checking for changes after each. No change. In the passenger-side kickpanel box, I pulled and checked every fuse. No issues found. The fuse box also contains several relays of two different types. I began swapping positions of like-type relays to see whether the problem would move. After swapping the relays in positions R202 and R203 (the final pair to try – figures, right?) all the symptoms disappeared!

The truck cranked and started; the CP9599 connected and displayed DTC P1000 (which is normal after a PCM reset). I swapped the relays back to their original positions and the problem returned in all its glory. Relay R203 is documented as PCM power.

The original engineering part number for R203 was F57B-14B192-AA. It’s been superseded by Ford part number F5TZ-14N089-B, which costs about $15 from the dealer. I sprung for a pair of ’em, figuring a spare might be handy.

The truck is running normally now but there’s still a some work to do. I want to mount the FPDM on standoffs, which should halt the dissimilar metal corrosion. This ‘mounting on standoffs’ is part of the repair kit if you buy a replacement FPDM from Ford. Also, when in the fuse box, I found a significant amount of water in the passenger side rocker panel, which leads back from the area under the fuse box. I found the water accidentally. When pulling fuses from the back of the fuse box it seemed as though a dropped fuse could be troublesome to retrieve, so I reached down to see how hard that might be. There are no electrical connections in the rocker panel tunnel, only wire bundles, but I did find some evidence of moisture on a few fuse blades during my check. There’s water getting in there from somewhere! Online, some owners have mentioned trouble with gasket sealing on the brake/bed light housing, and I’ve had that off several times over the years. But I also have a sunroof. More investigation of the water’s source is needed.