2010 Expedition Intermittent No Start/No Crank

[dkarrels]

Hi All,

Starting yesterday, my 2010 Ford Expedition began exhibiting an intermittent no crank/no start concern. I drove it to the auto hobby shop to change the oil; it started fine for the short trip (~5 minute drive). After arrival, it would not start -- no crank, no start, no headlight dim. I came back several hours later and it again started on the first attempt, and refused to turn over on each successive attempt. I was able to jump the 12V high-power pins on the starter relay housing to jump start it and drive home. Since then, I have been troubleshooting.

Diagnostic steps and results:
- Placed multimeter on the low power line to the starter solenoid. When turning the key to start, no voltage is reported at the solenoid. If I hot wire the starter relay, I see 12V at the solenoid and it starts fine. This, I believe, rules out the starter and starter solenoid as being the problem.
- I swapped the starter relay with other relays with no results.
- I bench tested the starter relay and it appears to work fine.
- When turning the key to start, the low power inputs to the starter relay show 9.7V-10V. I expected this to be 12V, and if I connet the two high power pins of the starter relay housing it cranks easily.
- I checked ForScan and the computer is sending a signal to the starter relay every time, indicating the computer sees no faults in the system, including the transmission position sensor.

Any ideas on how to proceed or where to check next?

Thanks.

 

[BigOleFordFan]

You can check my other posts on this subject about my 011 Expy EL, but suffice it to say that I have recently learned that there are at least 4 relays, if not more, which apparently are connected to multiple systems throughout the vehicle, and wired so that if one or more goes bad, it may or may not cause what you are describing....

Now 6 months & $1200 worth of diagnostics & parts later, I can finally count on it starting reliably

Also: "When turning the key to start, the low power inputs to the starter relay show 9.7V-10V. I expected this to be 12V, and if I connect the two high power pins of the starter relay housing it cranks easily"

There are alot of other posts here that seem to indicate this and/or possibly the relay failures could be caused by bad/leaking battery terminals, ill-fitting cables or insufficient grounding to the frame/body...perhaps something else you could check

Good luck !

 

[dkarrels]

I checked the cables and battery and they look good. My understanding is that the low side of the control signal to the starter relay goes to the PCM. When I turn the key to start, the PCM should evaluate the PATS condition, and if everything is good, short that signal to ground, which creates a circuit from the high side to the low side of the starter relay control circuit. However, the low side of the control circuit at the starter relay switches to OPEN (infinite resistance) when turning the key to run, as measured against the negative battery terminal (ground). If I'm understanding this correctly, then the PCM is blocking the start from occurring.

Simultaneously, through ForScan, I see that the SMC_MON PID remains Off throughout (ignition in Run or Start). I can't seem to figure out what would cause that PID to stay Off.

The PATSENABL stays Enabled throughout also, but the documentation in ForScan doesn't indicate if that's good or bad. I assume Enabled is good since I see no flashing keys in the instrument cluster.

Any ideas? How does the SMC_MON work? What should I check next?

 

[dkarrels]

Ok, so have continued troubleshooting. The picture shown here shows status so far. Here's what I have confirmed works:

- The battery, starter, starter solenoid and associated wiring. The engine starts by jumping the output circuit of the starter relay every time.
- All fuses and relays in the path from the ignition switch to the starter, with the possible exception of whatever is inside the PCM. I manually checked each relay and fuse in the starter circuits that I can find and swapped the relays around without solution.
- The ignition switch and Transmission Range Sensor (DTR). Verified by measuring the input voltage to the starter relay control circuit. It showed a solid 11.9V. ForScan also accurately reports the transmission sensor is in Park or Neutral.
- All wiring except for the link between the low side of the starter relay control circuit to the PCM. When measuring the low side (PCM side) of the relay control circuit, I see Open Circuit (infinite resistance) between that relay housing connection and the negative terminal of the battery in both ignition run and start condition. I think the PCM is supposed to short that terminal to ground if all start conditions are met, but that is not happening.

I have, I think, narrowed the problem down to one or more of these items:

- PCM. Since nothing has changed with the PCM, I assume the software logic is good, but maybe the internal relay that grounds the starter relay control circuit has broken. It could also be a corroded connection somewhere, but I have cleaned and tested as many as I can find.
- Wiring between the starter relay and the PCM.
- A start condition the PCM cares about that I can't seem to find in ForScan. Note my previous post about SMC_MON -- it stays "Off" regardless of what I do. However, I'm uncertain if that is normal...?

Here's what's limiting me at this point:
- I don't have a shop manual for the vehicle or a good wiring diagram. Anyone have one they can share?
- A better understanding of what SMC_MON means in ForScan. Is anyone willing to provide a status of SMC_MON for their vehicle during run and crank conditions? Maybe a freeze pane with the ignition in run but engine off, and while cranking?
- What other start conditions and sensors does the PCM use to enable start?
- Unknown unknowns -- I think I'm on the right track, but I could be missing something.

I'm running out of options and could use some help. Thanks.

 

[dkarrels]

Adding another confusing symptom to the list. Sometimes, and I am unable to determine which conditions prompt this, the car will start normally. I can sometimes start it another couple times in rapid succession, but if I let it run for a few minutes and then try to restart it, then it reverts back to this no crank/no start concern.

Any ideas what could be causing this intermittent behavior?

 

[Eddie Hudson]

I had a problem like that on my 2001 for over a year. The connector on the solenoid going to the starter switch ended up being loose. A little aluminum foil on the terminal fixed the problem.