I have an 09 SCrew 5.4L 4x4 with 118,000 miles on it. About a month ago, the truck went into Limp Home Mode (LHM) while I was on the highway. I got to the next exit, shut it off, and restarted it. The wrench went away, so I started off again. About a mile down the road it went back into LHM and this time gave me a CEL as well. I was just down the road from O'Reilly's, so I pulled in there and borrowed their code reader. Here are the codes I got:

U0100 - Lost communication with ECM/PCM
U0101 - Lost communication with TCM
U0073 - Control Module Communication Bus A Off

I pulled all the fuses associated with the PCM and swapped the PCM relay for the trailer light relay. Started it back up, and the wrench was gone but the CEL was still on. Drove it home, disconnected the battery, disconnected the PCM and TCM harness. Left it for a few hours and then reconnected everything. Took it for a drive and all was right with the world. No LHM, no CEL.

About 700 miles later, it happened again. This time I noticed that the truck seemed to be confused on which gear it needed to be in and I was getting a constant upshift/downshift. This time I took it to the dealer. They pulled the codes and got the same codes as the first time. I left it with them and they called me back the next day and informed me that they couldn't find anything wrong with the truck. They said they reflashed the PCM and TCM, and cleaned the contacts on the harnesses.

I picked it up and about 400 miles later, same thing. I went through the disconnect and reset exercise and made it about 50 miles before it did it again. Now it is doing it just about every time I drive it. I can always tell that it is about to do it because it starts searching for gears and the transmission is in utter confusion. I am really afraid that my PCM needs to be replaced.

Have any of you run across anything like this? I am really hoping someone on here can lend some insight and hopefully get me started on the right track to getting my truck back to a useable state. Thanks in advance for any help you might be able to give me.

 

I would go back to Ford with the electronic problems. Loosing communication with the TCM ? The limp mode would seem to be brought on by a low voltage problem with the electronic modules.

 

I second voltage issues.
if that truck has the factory battery in it, im sure its time for it to be replaced. my battery when I had an 09- bought new, lasted just over a year. then I started having weird things happen. it would just run weird, gauge check ( all gauges would go all the way over and back when starting).

if your alternator is not working correctly , it will throw some AC voltage into the system and also cause issues. I would have the alternator checked, and or replace, along with the battery.

 

Thank you for the tips. I replaced the battery about a year ago. I have not checked the alternator, but will be doing so today!

 

Could also be a failing ECM/PCM/TCM

Not sure if these are all in one modules or if they are separate.

 

U can do the HEC test, navigate to running voltage, drive it until it goes into limp mode and observe UR operating voltages. It will also give U dtc's while it does the other tests. Not all is Engineering gibberish with the Cluster Hec tests. U may be able to narrow down UR problems. I will hazard a guess it is between UR fusible links and the side kick plate area problem. Only a guess at this time though. Maybe water ? Maybe Battery or connections/fusible links? Most certain is a ecm area. I have heard of problems in the ECM electronic connector area ! It is a bunch of spaghetti there and some damage can occur in the areas. Usually a problem has been caused in production to this area of the harness. It would be great if U had a tester that would show U real time running graphs of the puter tests. I am assuming U have done fairly good maintenance to the truck and it has been tuned ect. UR tests will show U running temps if U can graph. Many times UR limp mode is actually caused by heat. Of course that would give a dtc area.

 

I tested the voltage on the battery with the truck off and it was 12.4. I started the truck and turned on everything (headlights, A/C, interior lights, etc) and put the leads back on the battery terminals and got 15.5 volts. I let it idle for about 5 minutes and tested it again and got 15.1 volts.

I will try the HEC test here in a while when I have some time.

The water question peaks my curiosity. Since this problem started, I have had a problem with a musty smell from the vents when I first start the truck. I searched like crazy trying to find the condensation drain to see if it was clogged and causing a buildup of condensation in the evaporator. I may be an idiot because I can't find the dang thing. I haven't noticed any water in the passenger floorboard, but if it is leaking into the kick panel that could be an issue.

 

The evaporator gets clogged with lint like a filter on a window ac unit caused by airborne chaff. It is a black nasty matte. This creates a musty smell also. Sounds like UR battery area Voltage is OK. Wonder where in the harness it drops? UR hec test voltage comes from the /dtc test system. When the reflash didn't solve the problem it indicates further diagnosis of the ECU is needed probably but U looking for moisture is good. U can also test UR battery condition by cranking the motor some. A good battery can crank for at least 1 minute by cranking without starting 10 times. If it runs down after say 20 seconds U got UR battery problem back. 1 of the best things U can do to test UR truck is get a code reader that will graph. Then U can look at soooooo much stuff about UR trucks electronic capabilities. In MHOP my best buy was such a code reader. It is fun also to watch it work. It is like U just filled the front of UR truck up with graphing gauges which U select one at a time. U can select whether it reads each graph in volts or time. It may show on 1 or more graphs where the volts drop off.

 

Removed your other thread of the same subject as only one is allowed. There were no responses anyway. Thanks
Jim

 

that battery voltage read while accys are in use seems a bit high. My radar detector, and programmer both have voltage read outs. I also too a true RMS meter with me and they are both within .1voltDC of each other.

I have a max voltage with AC and fans on high. cooling fans are blowing, radio is on, lights are on. and the highest I have ever seen it go is 14.2-14.3 volts.

im guessing it will actually start to climb higher. im thinking the battery has an internal issue.or alternator is getting close to its last breath. still leaning on the battery.
my 2009 did that exact same thing. battery voltage actually got up to 16.6v at one point. after two weeks of weird issues before I replaced the battery.
leaving it like this- I could see damaging things. im not sure how much voltage regulation is built into the electronics in these vehicles. im sure some as sensitive as some of the putters are.


water problems have been reported and if you have never noticed a wet spot on the floor passanger kick panel. it might be leaking enough to cause issues but I don't think it would cause over voltage issues like that.

after a long trip voltages are right at 13.8-13.9 after battery has been brought back up enough for the charge to slow down a bit.

 

I put it in the HEC test mode today on my way to work. The voltage that it was showing as I drove was from 13.2 to 13.7. Big difference from what I got with my meter.

I did notice something interesting though. The coolant temp got up to 112 Celsius. The temp gauge on the dash was still showing to be on the cool side. I don't know what exactly the standard operating temp for the 5.4 is though. I feel like this is high, but I am not 100% sure. If it is on the high side then my gauge on the dash is not operating correctly and high temps might be the source of my issues. What do y'all think?

 

That's 233 F and about 15 degrees too high. Not high enough to make the idiot light gauge move up though.

 

I would look at the temp problem, maybe the thermostat or clogged radiator with bugs. I would have expected the HEC to show around 210 as it is precise. Lower voltage usually occurs where the HEC is as the ECU is precise with its operating controls and usually lowers the mainline voltage. Looking slightly below 14v seems ok there. I would get concerned about a voltage much below 13 say in the 11 volt area as a loss or control problem. If U have a infra red meter U can quickly check the water temp at various metal places as it may be a bogus sensor.

 

Hello,

I'm curious if you ever figured out the issue.

I have a 2009 Screw FX4, 5.4 as well and have a similar issue with the LHM. I seem to only get the u0100 code (and that only happens sometimes). It seems to happen when it is only under about 55 F degrees outside (primarily in the morning). I've never seen it happen above 65 degrees outside. I would say it happens twice a week in the winter time. I've taken it to Ford and to two other mechanics, none of which were able to solve the problem. One mechanic blamed the TCM or internal connections of the transmission and took everything apart, tested everything, cleaned the connections and put it back together. That was not the resolution. This is why I'm curious if you were able to solve the issue, it sounds like it could be similar to your issue.

As far as the voltage issue, I haven't checked my alternator, but I do have about a 1 year old battery, which it happened before and after that installation so I don't think mine has anything to do with the battery.

I hope you figured out your issue. Please let me know if you did.

Thanks!

 

Hi tstalontsi,

How many miles do you have on your truck?

Ashley