I have a 2003 F350 6.0L with 115k. Lately I have been getting a P2138 and P2140 trouble codes. I found that means 'Throttle/Pedal Position Sensor/Switch "D" / "F" Voltage Correlation' and 'Throttle/Pedal Position Sensor/Switch "E" / "F" Voltage Correlation'. My first thought was the plug/wiring harness for the throttle positioning sensor on the pedal. It has not yet affected the truck in driving/running at all which is nice. Any ideas before I dump the money into it?

 

well i have the same issue right now except for the driving smoothly part. start your truck cold and rev it up to 2000 rpms. mine is smooth when cold. when you hit the first mark on your temp gauge, rev it again to the same. at this point my truck runs really choppy. if yours doesnt then your lucky. the problem could be your pedal servo but you need to check the mass airflow sensor and irp sensor. you have a temp probe in your intake. it engages different things when it warms up so the sensors report back to your pcm thru the pedal servo. give it a try and let me know as im in the same boat right now. oh and fyi. i pulled these codes with my superchips and no cel. the dealership told me there is nothing wrong and my truck is supposed to do that. you will notice when the system goes south, most likely the mass airflow, i lost a lot of power.

 

If you have those codes, you have a problem with either the pedal assembly or the wiring going to it. You can check the wiring for chafing but it is most likely the assembly and it will need to be replaced.

You may have other problems, but the only thing that can cause either of those codes is the pedal. If the problem worsens, eventually the pedal will quit and the truck will default to idle.

 

I have a question then. On the diagram it shows d and e going thru the mass air flow then back to the pcm. Could the pedal servo make my truck run choppy between 1600 elms and up when warm.

 

Sorry meant 1600 rpms

 

On what diagram? As far as I know, no sensor information goes through the pedal. It all goes directly to the PCM.

OK. I have found an electrical diagram for the 2004, which should be the same or similar to the 2003. I see the APP sharing VREF (filtered 5 volt power coming from the PCM) and ground with the MAP and BARO sensors. But the signal returns all go to the PCM.

It is theoretically possible that either the APP is messing up the VREF and causing errors in the signal return of the MAP sensor, or the MAP sensor is messing up the VREF and causing problems in the signal return of the APP. The latter is more likely, since it is APP codes you are getting.

The only way to know is to identify the VREF pins of the APP, attach a DVOM to it and watch to make sure it maintains a steady 5 volts.

 

okay here is where i admit im stupid and cant read. im going to test the return signal from my maf sensor when i get home today and test it. i will post what i find.

 

Is this the diagram that you're looking at?

If so, I can mark it up and make some notes and maybe explain it so that you understand it. Some of these sensors can actually get a bit complicated.

 

Okay. This is where I get lost. Does the signal from 3 on the map sensor even go thru circuit 5 on the pedal servo or is it just bridged to the signal line. I guess what I am asking is does the voltage come from one or another first or is it two separate points of entry all together. I don't know. Now I'm lost.

 

Hopefully I can help you make some sense of this. It can be a little confusing, partly because it's computer electronics stuff, and partly because they give labels that aren't defined, and in one case doesn't make any sense.

So first, a couple of definitions.

VREF. VREF is essentially filtered, regulated 5 volt current. VREF will always be 5 volts. As long as the PCM is getting 5 volts from the batteries, it will make VREF into 5 volts. The reason? Most of the sensors take that 5 volts and turn it into a voltage that represents the value of the sensor. If the sensor voltage input was battery voltage, for example, then the sensor output couldn't be relied upon, because battery voltage can range from 13 to 15 volts. If the voltage was changing, the PCM wouldn't know if it was because the sensor reading was changing, or because battery voltage was changing.

SIG RET. SIG RET, or signal return, is confusing. It would make you think that it is the output of the sensor back to the PCM. But it isn't. Signal return is basically an electrical path from the sensor back to ground. It's purpose is to make sure that any spurious electrical interference flying around the engine compartment, picked up by the sensor wiring, is sunk back to ground, not sent along the sensor wiring back to the PCM, where it could be confused with a sensor reading. For the purposes of diagnostics, I'm not sure that there is much reason to pay attention to the SIG RET lines. I think they are more confusing than anything else.

So, given those definitions, I give you the diagram below. It's the same as the last one I posted, except I've indicated all VREF paths in red, SIG RET paths in green, and actual sensor returns to the PCM in blue.

You'll notice that VREF comes from the PCM, is split more than once and sent to each of the 5 sensors in this diagram (one MAP, one BARO and three APP). You'll also notice that there are two VREF connections to the APP sensor group. One on the upper left and one on the upper right of the diagram.

Similarly, SIG RET comes from each of the 5 sensors and drains back to the PCM. With the APP group getting two SIG RET lines, just like it got two VREF lines.

Lastly, the actual sensor returns marked in blue return a voltage back to the PCM that varies based on what the sensor is sensing.

Hopefully, that will give you a better idea of what the diagrams are telling you.

As far as the problem you're experiencing, I'm not sure that the APP could cause the engine to run choppy, unless there is some sort of intermittent failure scenario going on. If that is the case though, it seems like the PCM would ultimately just fail back to idle until it got consistent returns from the APP.

What seems more likely to me is that you have something, either the MAP, BARO, APP sensor, or the wiring in between shorting your VREF intermittently to ground. I could see where this could definitely cause your symptoms. Which is why I suggested you hook a digital voltmeter between VREF and ground and check to be sure you are getting a consistent 5 volts. It might not be exactly 5 volts, it may be 4.9 or 5.1, but it should be consistent and not change. If you see fluctuations in the VREF voltage, this is likely your problem. Unfortunately, finding the short could be difficult.

 

Well since the problem is temp related, I'm leaning towards a sensor. It only does it when the engine gets to the first temp mark. Runs smooth when cold. I'm gonna go do some voltage chasing and see what I find. Thanks a million for your help.

 

okay. here is what i got. i have a constant 5.003 volts steady to the map. but pin 5 on the map plug shows full battery voltage. i dont know if its supposed to or not but another code popped up when me and the wife came back from dinner. i checked the codes before i shut it off and now i have a new code i havent seen before. its P0113 - intake air temp circuit high output. the d/e and e/f pedal codes have not came back. i cannot figure out why i am getting these random codes and for that matter i cant find where the intake air sensor is unless its part of the map sensor. during my testing i kept clearing any codes i got from the map sensor so i could test it. i cleared them a total of 8 times and three times randomly that p0113 code popped up and sometimes didnt. i dont get it.

 

First off, I think you're confusing MAP and MAF.

The MAP sensor, the one shown in the diagram I posted, only has 3 wires to it. It is at the rear of the engine compartment, attached to the firewall, and has a rubber hose that runs to the intake manifold on top of the engine. It measures air pressure at the intake manifold and is used to calculate boost. The MAP sensor shares VREF with the APP, according to the above diagram.

The MAF (Mass Air Flow) sensor is attached to the air intake tube between the air cleaner and the turbo charger. It has a 6 wire connector. It measures the amount of air flowing through that tube, and also contains the AIT (Air Intake Temperature) sensor. The MAF sensor does not share any wiring with any other sensor.

The MAF sensor does have 12 volts to it, on pin 2 according to the wiring diagram. It might say pin 5 on the connector, though. It wouldn't be the first time I've seen connectors labeled differently when compared to the service manual.

If you removed the MAF sensor and didn't get it back on tightly, it might cause the P0113. Because the MAF assembly also contains the air intake temperature sensor.

 

......... hmmm that would be a major setback in my testing now wouldn't it. Guess I better go check the right sensor. Explains a lot tho.

 

Now for the dumb question. Where is the map sensor.