Limp mode after ten minutes of driving?

Tiny
DRJAYSULLY
  • MEMBER
  • 2011 FORD EXPEDITION
  • 5.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 266,500 MILES
My vehicle listed above goes into constant limp mode after driving for about 10 minutes. I have replaced the plugs and the throttle body but still there. I can turn it off briefly while driving with a portable scanner but no codes except lost communication with the TCM and evaporative system malfunction. Clearing the codes only works sometimes because the scan tool will no longer get any signals from the PCM it seems. All the lights flash in warning. If I stop and turn off the engine it will not start, will not do anything at all for about 5-10 minutes and then starts right up. Should I be looking at the TCM, O2 sensors, some miscellaneous wire that could be anywhere? I have no idea where to look to solve this and can't keep throwing parts at it. Please, I beg of you, please help.
Friday, April 11th, 2025 AT 5:58 PM

2 Replies

Tiny
AL514
  • MECHANIC
  • 5,318 POSTS
Hello, it sounds like the vehicle is going into limp mode due to the loss of communication issue. What are all the codes you are getting? And these codes are set in the PCM I assume or does your scan tool read the entire network and pull codes from all the modules in the vehicle? It's possible that another module is taking down the network, or something is affecting the PCM alone, if the PCM is completely down during the fault, usually the check engine light will not light up when the key is turned to the on position. As it will under normal, non-fault circumstances. But knowing what module you are getting codes from is a start.
Since the PCM is on the High speed Canbus network, when the fault occurs, you could check pins 6 and 14 at the data link connector with a multimeter and see if they are reading 0volts or 12volts, meaning something is shorting the network to power or ground. This also sounds like a thermal issue, with something getting hot after your 10 minute running time, and then cooling off, so the vehicle restarts. I have seen solder joints on these Fords cracked a lot, The solder joint gets hot, and it expands opening the circuit, and once it cools off the solder joint closes back up, and the circuit is ok again until it gets hot once more. It's also possible for a sensor to short out and pull the 5volt reference circuit down, this can disable the PCM as well.
Post the codes here first and I will pull up some wiring diagrams for you.
Something else really quick, is don't move the wiring harness around yet, let's get you set up to do some testing so you're ready when the fault happens again.
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Saturday, April 12th, 2025 AT 10:59 AM
Tiny
AL514
  • MECHANIC
  • 5,318 POSTS
Diagrams 1,2 are for checking if the PCM power relay during the fault, showing the fuses that should have power with the key On.
Diagrams 3,4 are checking the throttle position sensor's 5volt reference (because it's easy to get to) and the APP sensor on the gas pedal. During the fault, check with the key on that these sensors have 5volts on labelled wires, a shorted 5v reference can cause the PCM to go down.
You should be able to see the APP (gas pedal) movement in the live engine data on your scan tool, key on, pressing the pedal you should see it sweep from 0-5volts or 5-0volts with no dropouts in the signal.

Then diagrams 5,6 are the Cylinder Head Temperature sensor, which can also cause the PCM to go into Limp mode to protect the engine from overheating.
the intermittent PCM no communications issue might be a power loss, in which case I would check the PCMs powers and grounds to make sure they are ok, but here's some starting points and things to check with a multimeter. If the PCM still communicates go into the live data and see if anything looks out of place, like a high engine temperature, but post the codes you have seen set as well.
If you don't see anything that looks questionable, we can see if the PCM is losing power. The turning the engine off and it won't restart statement sounds like something is getting hot and faulting, then cooling off allowing a restart. Check the relay pins and fuses for signs of overheating, they can be pretty obvious, looking semi melted or having dark pins. Let us know what you find, and we will go from there.

https://www.2carpros.com/articles/reduced-power-limp-mode

https://www.2carpros.com/articles/how-to-use-a-voltmeter
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Saturday, April 12th, 2025 AT 1:02 PM

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