I've been dealing with Ford for the past two years trying to troubleshoot why my 2021 Ford F250 diesel will not start when temperature drops below around 50F. This is an intermittent problem that is driving me crazy. I'm convinced it is something with the electrical power distribution system where if it gets to cold something is contracting and not making proper contact. Is anyone aware of any temperature sensor that go into the starting software as a safety interlock that I could also check. I'm wondering is there is a bad thermocouple or temperature switch. We have replaced the control module, cable harness to fuse box, and ignition switch to date.
Any troubleshooting ideas or fixes for similar issues is greatly appreciated.

 

When you say it will not start, exactly what if anything does it do?
Does it not crank over ?
Does it crank over , but not fire up and start running?
The more info you can provide the better, thanks.

 

Truck has power and all dashboard displays illuminate and radio works. when I turn the ignition key, I don’t hear anything click or try to start. It appears know Power is getting to the glow plugs. When I released the ignition key, you can hear it go through a shut down sequence where I believe relays or solenoids are deenergizing. It is a very intermittent problem that only appears when it gets colder than 50°. I think the problem is getting worse because before it would be able to go into the low 40s and still start. I’m wondering if there is a temperature sensor that is not calibrated properly at low temperatures, and is sending a failed to start signal to the ignition sequence.

 

Possible explanation,
When things get cold they shrink,contract etc.
The most troublesome things are poor connections that either open up or provide resistance within the circuit and -prevent or interfere with circuit function.
Can you tell us what the anti theft lamp does when it will not crank over the engine?

The engine will usually attempt to start, but will not start easily if there is a glow plug problem.

 

I am not 100% positive of what you’re talking about with regards to the theft light. After you mentioned, as I did notice that I have been seeing the set alarm option come up more often. Asking me to choose between all sensors or perimeter sensor which I don’t recall seeing as often in the warmer months.

over the last 3 days the truck has been plugged into a heater block and it started just fine. I’m not sure if it is just a coincidence or has something to do with the actual problem.

truck is currently in with the dealer for the next week to week and a half for them to work on

 

A suggestion for what it is worth,
Call the service dept every day and get an answer as to whether or not your vehicle has been brought into the shop.

I have dealt with dealerships and there are times you vehicle will sit outside in the lot until they get to it.

We try not to be a PITA , but there is nothing wrong with following up. If you get an answer that it will come in tomorrow , call and make sure it did get in.

I had an excellent relationship with one dealership service dept and when I went to see if the truck was in the shop, It was still out in the lot. I was running a fleet and this kinda embarrased the service mgr some, but we got the picture. After that they were always truthful to me.