2010 Expedition, starting issues. Starter replaced twice, need next culprit...

[BigOleFordFan]

Does your anti-theft light in the dash flash quickly when this happens? Had an issue similar in an 07 Lincoln MKZ that I had, and the problem was the PATS (anti-theft module) in the instrument cluster was bad. It was an intermittent problem, which made it hard to figure out, but replacing that seemed to help the problem.

I would also agree to check/swap the starter relay to eliminate that possibility. And the corroded cable end seems to be a possibility as well.

The fact that it starts fine when it does start, eliminates the battery as the problem.

This is almost exactly what was happening with my 011 EL Limited....and I did have the flashing padlock PATS light, as well as a brand new battery, cables and wiring harnesses...

It took 3 months & $3k worth of diagnostics, replacing both keys, the ignition switch, the HALO sensor, removing the remote start module, and checking most of the other stuff mentioned in this thread too.....the last dealership I took it to said the "Run/Start relay" was fried, which they replaced and it starts reliably every time now for over a month...

Fingers crossed

 

[dkarrels]

I'm having what seems like this exact issue. I can add this to the conversation:

- I used ForScan to troubleshoot this problem. Even when the car refused to crank, I saw that the computer was commanding the starter relay to enable. This shows that, for me at least, all of the sensors were providing input to the computer and it tried to start the engine. This, again for me, rules out the neutral position sensor and ignition switch as those are both inputs to the computer in support of the start decision. I monitored the input pins on the starter relay also in this diagnosis and saw it go from -1.5V to 9.7V-10.0V. This shows that the car is flipping all of the upstream relays in favor of trying to start. However that relay is not activating. Switching that relay with another doesn't seem to work so I suspect the issue is the voltage to that relay is too low, suggesting a corroded/loose wire upstream. Still working to find it. And now that I write this, I'm wondering if those connectors should be at 0.0V instead of -1.5V -- this *could* indicate a short somewhere. If the command input to that relay started at 0V and added 11.2V (-1.5->9.7), I suspect it would start.
- A takeaway here is that this condition has a work around. If I pull the starter relay, I can run a jumper wire between the high power connectors in the relay housing and it turns over and starts. Every time. I'm still not willing to use this as a solution, but it does at least offer an option if you really need to drive the vehicle.

I'll post here as I learn more.