Hey all, a few weeks back my truck went into limp mode. I pulled Code P2127 "Throttle/Pedal Position Sensor/Switch E circuit low input". With a brief search of this forum I decided to replace the throttle body. I disconnected the battery for 30 minutes, reconnected, then went through the process of resetting the TPS. All worked.....for two days. Then back in limp mode. Figured it must be the APP Sensor. Took it to my local dealer for a tech to diagnose the problem. Tech confirmed the APP Sensor was bad and told me he could watch the voltage dancing all over the place. Took my truck home, replaced the Accelrator pedal assembly, disconnected battery for 30 min, reconnected battery, then went through TPS Sensor reset process. Drove 30 ft and the truck went into limp mode again! Said some choice words, pouted a bit, then pulled it back into the garage. I pulled the 6 pin connector back off, tested voltage on pins 1 and 6 and got 5v on pin 1 and 4.5v on pin 6.

Now that you know what all I've tried (sorry for the long explanation) I've got two questions:
1. Should I be concerned that I have 4.5v vs 5v on pin 6?
2. Does the ECM need to be reflashed now that I've replaced both the throttle body and the APP Sensor?

I'm pulling what's left of my hair out right now!!

 

Before you do anything, go under the hood and look for the ECM, it will have a few large connectors with a bunch of wires and disconnect all of them, inspect the harness pins for being pushed back/out and/or corrosion repair/clean as needed and go for a test drive.

ECM will look like this top center of pic on firewall.




Rotate those grey levers back and it will disconnect the wiring from the ECM so you can inspect.

To reconnect just push the harness plugs back into the ECM and rotate the levers forward till they stop.
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Thanks for for the reply.

sSo I removed the connectors at the ECM and inspected and didn't see anything of concern. I also remove the connector at the throttlebody and inspected that as well. The throttlebody like I had mentioned is new, but I decided to take some voltage measurements at that pin connector. On this 6 pin connector, the far left pin has 10v and the far right pin has 3.5v. Are both of these pins supposed to be at 5v as well?

 

Did you test drive the truck after reconnecting the ECM?
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I did. This time I made it half a block before it went back into limp mode. Progress? 🤣

 

So clearing the code, does the vehicle idle fine? Can you rev(move the pedal) without it being in Drive? Does reving set a code? For how long does it stay code free? Are the rpms registering? Can you watch the voltages through a scanner or back probe? Is the ground clean?

 

Yes, always idles fine whether the wrench light (limp mode) is active or not. When I first start it, there's always no wrench light and the truck operates as normal for typically a few seconds before going into limp mode. RPMs are registering fine and reving the engine if repeated will indeed throw the truck into limp mode.

I dont have a scanner (I had pulled the p2127 code using the enhanced scanner at my local AutoZone) so I don't have a way to watch the Sensor voltage while the connector is connected.

And last, how would I determine if the ground is clean?

thanks for the help!

 

Do you have access to the wiring diagram? Access to DVOM? Disconnect battery, unplug Ecm connection and throttle connection along with app. Match up pins to each item. Ecm to app and Ecm to tps. Test wiring for short to each other, ground and power.

You replaced the items so test wiring. If wiring good can be two things Ecm or possibly another component inference.

Anyway other work lately? Or mods?

I would reinspect the pins very well maybe removing the back covers to verify. From your above description of immediately setting sounds like wiring or ECM

 

I don't have access to the wiring diagram. I need to find a PDF online so I can do like you suggest and see if I can find a short. Question on that though is wouldn't a short pop a fuse or something?

And no, I haven't modified anything. I'll let you know what I find. Thanks again for the help.

 

So I ended up taking my truck back to the local Ford dealer and they hooked my truck back up to their diagnostic machine and long story short they found a short in the main harness. They fixed it for me and all is well now. I was a little frustrated that I replaced the throttle body and accelerator pedal assembly for nothing, but at the end of the day they didn't charge me for finding and fixing the short, so it all works out in the end. I'm just disappointed in my troubleshooting skills!

Thanks to those that chimed in and helped. It's much appreciated to have this community of brilliant minds to offer help!