2006 Expedition won't start, PATS light always on, no OBD communication, data errors

[dmaz]

First post, but have been reading the forum for years, and have made great use of all the accumulated wisdom on here. My thanks to you all!

Meanwhile, my beloved, ever-reliable Expy is now driving me nuts – starting the day after I told someone it had been my best Expy EVER! That'll teach me . . . Here's the story:

A few months back, experienced a no-start at my doctor's parking lot in CA. Diagnosed bad starter, Ubered to Harbor Freight, bought jack, ramps, and a starter from AutoZone and fixed it where it sat, much to the amusement of the doctor's staff. Took me half the frickin' day to get that damn top bolt out. Started right up, tho. By the way, as a tip to anyone trying to get at that top bolt, the easiest way to get at it is with a short swivel socket hooked to an 8" extension and a ratchet with a swiveling handle to clear the neighboring parts.

In the intervening months, I noticed the starting becoming less eager, coupled with an issue of overnight battery drain, leading to frequent charges after failures to crank. Figured the battery was shot, which testing showed it was. New battery installed last week. No crank, no start.

Bought another starter and installed it (since I had bought the cheap one). Took me 25 minutes that time, LOL. Still no crank, no start.

I have read every posting I can find on this subject, and have followed many of the suggestions, including:

• R&R battery terminals after stripping cable ends.
• Checked and tested fuses and relays, including for the fuel pump control module.
• Checked and tested fusible links
• Replaced solenoid pigtail per TSB 06-19-14
• Unbolted, sanded and reinstalled relevant grounds (including the one that requires removing the right headlight).
• Jiggled the key, and tried starting with the shifter in neutral
• Replaced battery in key fob

Here are the current symptoms:

• PATS light is ALWAYS on and steady. No flashing at any time.
• Key fob functions normally to lock and unlock.
• MFD shows "engine temp data error", charging system data error"
• My Autel MX808 cannot communicate with the car, stating communication errors
• Key functions are otherwise normal. Gauges appear normal. The precise symptom that may point to an answer is that if I turn on the ignition, wait (even for a second) and then turn to start, nothing happens. Zip, zero, nada. However, I turn the key from "off" to "start" in one quick motion, the starter relay will click and the starter motor will crank for just a fraction of a second before stopping.
• There was one strange symptom right after I cleaned up and reinstalled ground G102: the start would crank and stop super fast, kind of like machine gun fire as long as the key was held in the start position. This symptom is no longer present.

My thinking is that something in the system is commanding the vehicle not to start. So when I turn the key to the ignition position, hold it there for a bit, and go to start after that, the electronics are preventing the starter from cranking altogether. But when I turn the from off to start, the relay engages and the starter briefly cranks before being shut off. Without being able to get my tablet hooked up, I can't read any codes to try and figure that out.

I'm suspicious there may still be a bad ground somewhere, or the PATS or PCM got scrambled because of the MANY times the battery went dead.

What are my next diagnostic or repair steps, esteemed colleagues? Anyone seen these symptoms? Thanks in advance!!

 

[Yupster Dog]

What are my next diagnostic or repair steps

Voltage drop test.

https://www.expeditionforum.com/threads/voltage-drop-testing-for-no-start.26144/

 

[Trainmaster]

Have you looked at a schematic of the starting circuit to see what's involved with cranking the starter. A relay perhaps?

 

[dmaz]

Thanks for the responses. I did a voltage drop test, and the positive cable from battery to starter solenoid went from 12.6 volts to 11.5. Does that mean I have to replace the harness? Presumption of internal corrosion?

 

[Yupster Dog]

Thanks for the responses. I did a voltage drop test, and the positive cable from battery to starter solenoid went from 12.6 volts to 11.5. Does that mean I have to replace the harness? Presumption of internal corrosion?

Not necessarily, the connections just may need to be cleaned and properly tightened. I would start there and then if you get the same result yes a new wire would be in your future. Don't forget to voltage drop test the ground wires as well.

 

[TJ Hessmon]

This may sound nutty but I have experienced the same problem with a Mustang.... turn your HVAC system off, and try cranking the vehicle again.... especially if ... you have an aftermarket radio...

Next there is the off chance your keys internal RFID is mo longer working. Try one of your spare keys....

other common issues,
Initially the park and brake interlock switch (very common on Fords), causes exactly your stated condition....

Another is the neutral safety switch

After these its on to the wiring diagram

 

[dmaz]

Once again thanks for all for the help. We had a storm come through, and the Expy is in an adjacent parking area with no cover, so it has taken me a bit to get back to it. @TJ Hessmon, I am all for nutty, and yes, it has an aftermarket radio, but unfortunately, no change in symptoms with that suggestion.

Here is the full update: I was able to do voltage drop tests on both the positive and ground cable, and found drops in both cases. I therefore ordered a replacement starter harness and installed it yesterday. Again, no change. Exactly the same symptoms.

I remain suspicious that it's a PATS or some other thing, particularly since the PATS light never goes out. Plus I have only one key. Sigh. This is beginning to look suspiciously like a stealership-only issue, unless I can find one of those geeky guys with a computer that travels around reflashing. Meanwhile, I will check the interlock switch and the safety switch next.``````

 

[Hamfisted]

Are you the original owner ? Do you have any other ignition keys you can try ? Is there a remote start module installed under the dash ?