While driving home last night from a cross-country trip to spend time with family for turkey day, I was about an hour from home and the oddest thing happened.

I approached a hill that, while not very long, is unusually steep. I had my cruise set at 70. As I started up the hill, the transmission shifted down into 4th and the engine's RPM went up. Nothing unusual. As the incline started to level off, the truck decided 3rd gear was needed. When it did so, the truck suddenly dropped to 69.... again, nothing unusual. The engine revved up as one would expect.

I was thinking that as soon as the speedo reached 70 again, it would jump back up into 4th, and as the top of the hill leveled off, I'd be in OD again. But after the engine revved up in 3rd, it just as quickly went to idle (as idle as it could go in 3rd gear at 69MPH). I looked at the dash and my speed was dropping.... 66...64....62......

I pushed on the accelerator pedal and was able to get back up to 70 without receiving a Kenworth enema. It was then I noticed the cruise had turned off. I pressed the Resume button, but nothing. It was only after I turned the cruise back on and set it did it re-engage.

If I'm not mistaken, there's a sensor somewhere on the truck that 'detects' a crash and turns off the cruise (I'm not referring to the one that turns off the fuel pump!). But the lurch wasn't that violent. I've hit potholes that felt worse.

Anyone have any idea what might have caused this? A fluke? Aliens?

 

Good to include year of Ranger
2009?

No, there is no sensor for accident, specifically
Cruise will shut off if
Brake pedal use, there are 2 switches for this
Clutch pedal(manual)
Sudden speed change, up or down
And of course the buttons

Brake pedal has a switch that grounds cruise when pedal is up, and sends it 12v when pedal is pressed, turning cruise off, basically "Brake Light" part of the switch
And another switch that sends cruise 12v when pedal is up, and cuts the 12v when pedal is pressed, turning off cruise
You don't have a clutch pedal, but pedal down shuts off cruise
Sudden drop in speed, accident, would cause cruise to shut off
Slow drop in speed will also shut off cruise, not sure of parameters, but I would think 8 to10mph drop for sure

Buttons on steering wheel and clock spring, not sure what 2009 speed control buttons are like but in earlier years they could cause problems as they got older
When cruise is on there needs to be a constant connection between buttons and cruise module, momentary loss of connection shuts off cruise

 

Yes... 2009 w/auto.

But if the brake was used (either accidentally with foot or it is so sensitive a lurch would cause it to trigger the brake light switch), pressing the Resume should engage it again. I had to turn the cruise back on.

 

Yes, which is why I mentioned that the buttons need to be in constant contact when cruise is on other wise it turns off completely
Ford never publishes module software, so you and I are both just guessing at this point unless this shut off can be repeated reliably, which would tell you the problem but hopefully it was just a glitch and won't repeat