2006 Expedition - Electrical Issue(s)

I realize electrical issues on a vehicle can be hard to narrow down, but here's hoping some direction can be provided on where to look. I am an engineer and experienced troubleshooting electrical issues, as long as I have good information and schematics to follow.

Our 2006 Expedition recently experienced numerous anomalies that seem unrelated but could be tied together somehow. First, the rear hatch window unlatches whenever the A/C is turned on. The headlights in the Auto position will also turn on, even in daylight, when the A/C is turned on.

Attempts to lock the doors via the door lock switch or the key fob also causes the rear hatch window to unlatch.

The A/C blower will not increase its speed through the four speed selections, and switch to the fourth (highest) speed causes the engine to shut down. I understand this might be a power saving feature the engine computer invokes if it senses an issue in the vehicle.

When these issues first occurred I contacted a supplier of reconditioned engine computers, one I had success with on replacing a computer on my 2006 F150 in 2018 (still running great). I ordered a new computer, installed it and the vehicle behaved normally for almost five (5) weeks, and then all the same issues returned.

I contacted the computer supplier and had another one sent to me under warranty. I just installed it and the issues remain.

I am wondering if is there a way to isolate certain circuits, one by one, and see if one of those circuits might have a bad wire. For example, maybe the rear hatch window latch or door sensor is causing the issue and is affecting other circuits related to the A/C, headlights and door locks. Or one of those other circuits causing the issue. I'm thinking of pulling fuses for those circuits one by one to see if doing so might reveal something.

The issues I am having seem too varied to offer one specific solution, given that I have already tried two different engine computers, but some general tips on electrical troubleshooting would be much appreciated.

Thank you all...

Wow that is variety of issues. You're right it could be a single issue causing the others. My transfer case shift motor was causing issues for multiple computer modules and sensors. I stumbled on that resolution while chasing down vibration though.

You may need a resource like AllDataDIY to have all the wiring schematics/diagrams handy I think.

A good place to start would be a voltage drop test on the wires associated with the systems showing systems.

There are some far more experienced members than I that may have a thought that will provide a more isolated starting point.

Thanks for the suggestions. I was due for a new battery so I replaced it after my original post, hoping that may have been the issue. The voltage was decent but it's been scorching hot here in Florida the past month so I wondered if it might have had a bad cell that was causing the issue. No luck.

I am begging to suspect a loose wire or a grounding issue because the issue is intermittent. Before I replaced the battery I had a scanner connected to the OBD port and noticed the voltage with the A/C off was > 13V, but with it on it drops to ~12V. I haven't rechecked with the new battery, although with the engine running I would expect the alternator to be putting out ~14V.

Nevertheless, the issues with the locks and rear hatch window occur with the engine off, so that's why are I'm suspecting a loose wire or grounding issue.

I have read some threads which mention the wire bundle behind the passenger side kick panel, specifically a ground wire or a spliced red/white stripe wire in that location causing trouble. That's my next step.

Thanks for the tip on AllDataDIY for the WDs.

DAY 2 UPDATE

The vehicle sat for about 24 hours, mainly because I had other things to do before I could get back to it. The first thing I did before cranking it up was to put a digital multimeter (DMM) in series with the negative cable at the battery and monitored the amps per a TSB I had read about excessive key off load (KOL) and battery drain. Even though I haven't experienced battery drain I thought it a good test to perform to check whether anything was activating that was not apparent. The readings average around 24 mA with the occasional periodic jumps which were expected per the TSB. Nothing appeared unusual from that test.

I removed the DMM, reconnected the negative cable to the battery, switched the DMM to volts to read the voltage at the battery. I cranked the engine and everything seemed normal. No issues at all. The voltage with the engine off was ~12.6V and with the engine running it was a little over 14V. Again, everything seemed fine. The A/C worked normally, the headlights stayed off, and the rear hatch window remained latched.

I have an OBD scanner so I looked at a few other readings and nothing seemed unusual. I ran the engine for about 10 minutes, switched it off, and then checked the door locks from the key fob and the door switches. Everything worked fine.

I switched the engine off, then back on again after a few minutes. Once again, all was well.

I let the vehicle sit for a few hours while I cleaned up and worked on dinner. After dinner I went to move the vehicle and as soon as I cranked the engine the rear hatch window unlatched and I couldn't shift out of park. I noticed I had started the engine with the A/C turned on and it wouldn't adjust speed, so I turned the A/C off, and I could then shift out of park. I suspect the A/C not adjusting speed and not being able to shift out of park was a power conservation feature initiated by one of the modules.

I then tested all the things (door locks, headlights, etc.) that had been malfunctioning, and all the issues had returned.

I moved the vehicle into the carport and turned off the engine. I noticed both the turn signal indicators and the high beam indicator on the instrument panel were all dimly illuminated, but none of those lamps were actually on. I tried the door locks from the door switch, but none of the locks functioned and the rear window unlatched. I could not relatch it.

I removed the negative terminal from the battery then reconnected it. This made the turn signal indicators and high beam indicator go out, and I was able to latch the rear window, but pressing the door lock switch at the door again unlatched the rear window, but didn't activate the locks. I could relatch the window this time.

My next step is to look at the wire bundle behind the passenger kick panel and possibly removing some fuses one by one to isolate some circuits.

This list of grounds might prove to be useful. It's from a 2003, matched my 2004 though and I suspect it'll be close if not the same for your 2006. Poor grounds can certainly cause some strange issues.

Thanks! I'll report what I find...

I have a 1998 Expy that had some of the same issues you had. I finally found the problem which was the Gem module. After replacing the Gem all the problems went away. My Gem was attached to the backside of the fusebox.

Thanks. I will be able to get back to this later this week so I'll report what I find.

Is anything required to replace the GEM module, e.g. matching or programming the new module to the original, etc., or is it a simple swap?

THe Gem module comes preprogrammed. It is a simple swap out.

Thank you all for the suggestions. I have been gone but ready to keep looking into this issue tomorrow and through the weekend.

I had ordered the Workshop Manual and Wiring Diagrams books for the 2006 Expedition, and they arrived while I was away. Lots of good stuff to dig into. While looking for information about the GEM module it appears the 2006 (and possibly a few years prior) have a Vehicle Security Module (VSM) instead of the GEM module. I cannot find any reference in the books to a GEM module, only the VSM.

So, the issue still may be with the VSM, but the Workshop Manual specifically states "...it is necessary to upload the module configuration ... [and the] information must be downloaded to the new [VSM]...".

I will search this forum, but any suggestions on where to purchase a replacement VSM and have the old VSM configuration loaded into the replacement? The manual says use the diagnostic tool which I do not have. I hesitate going to the Ford dealer for the part and labor.

My next step is the locate and inspect the VSM, plus inspect different grounding points around the vehicle for possible issues.

Thanks for the continued suggestions.