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.

 

[touchdowntexas]

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?

Did you ever get this figured out? I've got a 2012 F150 showing the same behavior. Intermittent start issues, but the truck always starts if I jump the starter relay pins. Forscan seems to show all of the relevant BCM PID's as ready to start. On the PCM side I get the same SMC_MON "OFF" when trying to start, even though other PID's seem to be OK (STARTREQ_CAN "YES"). I also see STRT_RLY "DISABLED".

Seems to be either the PCM, or a wire/connector coming into or leaving the PCM. But I'm totally stumped and feel I'm at the point to take it to the dealership.

 

[dkarrels]

Yes, I did finally find and fix the problem. In order for the starter circuit to energize, the Starter Relay needs to close -- Pin 1 receives +12V and Pin 2 goes to ground completing the control circuit for the Starter Relay, thus closing Pins 3 and 5 and providing power to the starter motor. What took me a little while to figure out is that the PCM controls the path to ground from the Starter Relay Pin 2, through the PCM, and finally to ground. In essence, the PCM connects its Pin 7 on Connector C175B input to ground, which closes the Starter Relay control circuit. This is the mechanism the PCM uses to ensure all other sensor checks are valid to allow the motor to start (security, key position, transmission position, etc.).

What apparently broke in my Expedition is that the PCM no longer connects the starter relay low side (Pin 2)/C175B Pin 7 to ground -- I guess that PCM relay fried. I verified this first by checking the full wiring path from the ignition switch to Pin 7 on C175B -- the entire path demonstrated low resistance and was stable (no loose connections). I was able to manually jump Pin 7 on C175B to ground directly with the ignition switch in Start position and the vehicle started properly. This finally narrowed the issue down to PCM itself. I searched for several weeks for any indication that another sensor was malfunctioning before finally determining that the PCM was the issue. Apparently the SMC_MON value doesn't do anything relevant, at least as far as I can tell, for the starter circuit control.

From there, I ordered a remanufactured PCM. It arrived and had other problems that prevented things from working properly. I ordered a second PCM from a second remanufacturer only to discover it was programmed incorrectly. Both companies were difficult to deal with. I finally gave up and returned both of them. I was (and am) still too cheap buy a new PCM from Ford for such a simple issue.

Instead, I cut the Yellow wire that connects to C175B at the PCM, solder spliced and heat shrunk it to another cable, and connected it directly to the same ground the PCM uses just a few inches away. Since then, about 3 months now, it has worked flawlessly. I recognize that the PCM may be about to fail in some other way, but I will deal with that when it comes.

Hopefully this helps.

 

[touchdowntexas]

Thanks! This is my first time doing any real electrical diagnostic work, so apologies if my lingo isn't 100%. So the PCM sends a signal to send 12V to pin 1 AND closes some other internal relay to ground pin 2? That seems unnecessary and redundant. So you just connected to yellow wire to a constant ground (bypassing any internal switching)?

Before I go that route I think I should verify that pin 1 is getting 12V when turning the key to "start". If I don't get 12v then I guess I've got some other PCM/BCM issue. I should also test pin 2 to see if it's grounding properly, but not entirely sure how to do that.

 

[dkarrels]

Almost. The PCM doesn't send 12V to the relay. A couple things:

1) To crank the starter, two main things must occur: the ignition key and all upstream items must allow power to flow to Pin 1, and the PCM must connect Pin 2 to ground. This creates a closed circuit that allows power to flow from the battery, through the ignition switch and a few other elements, through the starter relay low-power/control circuit, and finally to ground.
2) The purpose of a relay is to use a low-power/control signal to close a high-power circuit. For the Starter Relay shown in my previous post, the +12V from the ignition circuit arrives at Pin 1 on the relay when the ignition switch is in start position and all upstream mechanical connections are closed, thus indicating the driver is trying to start the engine. In most cases, Pin 2 is already connected to ground, in which case the presence of +12V on Pin 1 closes the low-power/control circuit and allows current to flow between Pin 1 to Pin 2 on the relay, effectively activating the low power/control circuit within the relay. The presence of current flowing through the low-power circuit within the relay creates an electromagnetic flux that closes the high-power switch in the relay connecting Pins 3 and 5. Pins 3 and 5 represent the high-power side of the circuit and, when closed, allows enough power to flow to close the starter solenoid and crank the starter.
3) The design used by Ford, and I suspect rather common in the automotive industry, is for Pin 2 in the low-power/control side of the relay to remain disconnected from ground (open) unless the PCM closes it. This prevents current from flowing from Pin 1 to Pin 2, and thus does not create a flux that will close the switch between Pins 3 and 5 and so the starter does not activate. Inside of the PCM is effectively another relay that will connect the starter relay Pin 2 to ground when it is closed, which only happens when the PCM decides the engine should be allowed to start. At all other times, the PCM keeps that internal relay open, which keeps the low-power/control side of the starter relay open, which prevents the starter motor from cranking.
4) Using the below image, if you start at the SMART JUNCTION BOX, we can follow the circuit during a start request:
- F27 (Fuse #27 I think) is connected directly to the battery, so it always has +12V on it.
- Moving downward, out of the SMART JUNCTION BOX at connector C2280A and leading to connector C250 (Pin 9) at the ignition switch. This circuit is always hot (+12V). When the driver turns the key to Start, the switch moves over to Position 4, which connects the +12V from the SMART JUNCTION BOX to the output Pin 10.
- The +12V leaves the IGNITION SWITCH through connector C250 (Pin 10), through the remote starter system (if equipped), and eventually splitting and going to connector C175B (Pin 16) and the BATTERY JUNCTION BOX - START DIODE.
-- The presence of +12V at the connection to the PCM at C175B Pin 16 tells the PCM that the driver is requesting an engine start. Internal logic in the PCM activates some other checks and preparations for engine start.
-- A diode, such as the START DIODE, is used to ensure current only flows in one direction, in this case from the top of the picture to lower in the picture. Although the book doesn't say, I suspect that diode exists because providing power to the POWER DISTRIBUTION/SJB may introduce some risk of reverse power flow. Unless the diode is faulty, we can safely ignore it for this discussion.
-- On the low side of the BATTERY JUNCTION BOX (BJB) is a connection to the STARTING SYSTEM (20-1) at marker A. This is the connection to the picture in my previous post at the top. 20-1 is the page number in the manual I am using.
- At the top of page 20-1, at marker A, +12V should be present at CDC38, the White wire with a Violet stripe since the driver has requested an engine start (from the below picture).
- In this condition, CDC38 provides +12V power to the starter relay low-power/control circuit (Pin 1).
- The PCM, seeing the presence of +12V at Pin 16 (below pic) and therefore understanding that the driver is trying to start the engine, will make a decision. If all start conditions are met (as before: security, safety, transmission position, etc.), it will use an internal PCM relay to connect Connector C175B Pin 7 to ground, creating a closed circuit from the battery and through all of the above elements, and thus allow power to flow through the starter relay low-power/control circuit. If conditions are not met, or, in my case, the internal PCM relay is burned out, it will leave Pin 7 open (NOT connected to ground) and the starter relay low-power/control circuit will remain open, power will NOT flow through the starter relay low-power/control circuit, and the starter relay high-power switch (Pins 3 and 5) will remain open.
- If power starts flowing through the starter relay low-power/control circuit, it will create a flux that closes the high-power switch in the relay, connecting Pins 3 and 5, and allow high power to flow to the starter from Pin 5, through CDC25, and eventually to Connector C197B Pin 1 at the starter motor. Internally, that is the low-power/control side of the starter solenoid, which is just a big relay that allows/disallows starter power to flow from the battery (C1100C/A) to the starter itself.

To answer your questions:
- Testing for presence of +12V at starter relay Pin 1 is a good idea. I don't recall for sure, but it may only be hot when the ignition is in the start position. Be sure to measure against a good ground (don't try to use Pin 2 as the ground -- it is probably open/not grounded).
- If the PCM is working properly, and the wiring and connections are good, then testing starter relay to ground while the ignition is in the start position is also a good idea. If the PCM is faulty, or if a wire/connection between the BATTERY JUNCTION BOX and the PCM is bad, then it will be open. I *think* you can remove the starter relay and check for connectivity to ground while the ignition switch is in start because the PCM should see the signal from C175B Pin 16 below and therefore close its internal relay and connect starter relay Pin 2 to ground.
- Yes, I shorted the Yellow wire running into the PCM (Connector C175B Pin 7) to ground (being sure to leave myself enough wire at the PCM in case I wanted to undo it). That effetively bypasses what I believe is a burned out relay inside the PCM. I recommend you test this before cutting anything -- have someone turn the ignition key to start, and run a jumper from Pin 7 to the neighboring grounding block. Note that the wire at Pin 7 is very small and you will want to avoid jamming anything large in the back of the connector at the PCM as doing so could damage it. I think I used either a paperclip connected to a jumper from my multimeter, or something equivalent. If the starter turns over, then you have verified that everything up to the PCM is working as intended. This still doesn't entirely rule out of some other sensor the PCM is seeing as not allowing a start condition, but by staring at Forscan for a while you can probably gain some comfort if that is or is not the case.