Pending P1120 Code?

NewShockerGuy · #1 05-13-2017, 02:39 AM

I have a ultragauge on the windshield and just the other day it beeped telling me I have a pending code of P1120. Which I ran some searches and it comes up as the TPS sensor.

Thing is when I scan with an actual reader and even the ultragauge there are zero codes. Nothing is actually throwing the code and making it stay. I did notice twice however when reversing up my driveway it was shaking a little bit/idling weird. Other than that the truck drives fine, doesn't idle weird when start up or sitting at lights, or driving down the highway.

I ordered a new TPS sensor since they are cheap at $30 (oem motorcraft), should have it in a day or two. I figure the one that is on the truck is original being 16 years old.

Once I get it I plan on cleaning the MAF, and throttle body...normal stuff. Anything else I should be looking for?

Most of the time I can drive and this pending code doesn't come up.. .it's only been happening every other few days. IE: Happened once on Monday, was fine Tuesday/Wednesday, happened once on Thursday/Friday.

Note that my CEL is NOT on, nothing is flashing.

Thanks,
-Nigel

tomw0 · #2 05-13-2017, 06:56 AM

The TPS is a 'pot' or potentiometer. Its resistance changes over the range of its mechanical sweep. If there are worn spots, they may cause the signal or resistance to jump very quickly with little motion, or to go to zero/infinite at some really worn spots. The computer is likely noting the jump, and storing that is a pending code. There may be software that notes large changes in reading back and forth, and reports that as a pending code. I don't have knowledge of the code, but that's what I think is going on.
You can use a VOM from the 'sense' wire to ground(use the ground connection on the TPS) and sweep the sensor from closed to WOT, and watch for 'dropout' or 'jumps' of the reading. If you find them, you have good cause to replace the TPS.
One thing, if you have an automatic transmission, and your TPS is flaky, you might find the tach indicating jumps/drops in rpm as the lockup torque converter locks and unlocks. It is designed to unlock when the TPS is at 'idle', and the failing TPS may show 'idle' when you are traveling down the road @60, and unlock the converter. A smidge more or less throttle, and the converter re-locks about 5 seconds later.
tom

NewShockerGuy · #3 05-15-2017, 08:10 PM

So what you just mentioned as far as traveling 60mph and seeing the RPM go up and then down is happening to me. Has been for a while! I always thought it was because I went with larger tires and the truck didn't know what it wanted via overdrive, or no overdrive...lol That would make sense in a way.
Thank you for this piece of info Tom. I ordered the TPS sensor and it arrived only to find out the damn thing is for the newer models. I have to send it back and already have the correct one on order and will have it Thursday.

I will update this on Thursday. It would be super awesome if changing the TPS sensor would in fact make the truck stop fluctuating the RPMs/ up down when I am cruising on the highway.. It almost seemed like it kept searching for a gear via higher/lower..etc.

-Nigel

tomw0 · #4 05-16-2017, 06:04 AM

If you can find a section of relatively level pavement that will enable cruising at a given speed, and you note the upshift/downshift/lock/unlock syndrome, I'd seriously look at the TPS. Later model transmissions seem to shift and lock at will, mostly I notice the downshift when there is a little more work to do, as in climbing a slight hill.
If you've ever gone on the Interstate in OK, and turned on the cruise control, the upshift/downshift pattern will make you wish for an override. It cannot seem to make up its own mind, and the rpm surges are not good for fuel economy.
tom

NewShockerGuy · #5 05-17-2017, 12:08 AM

Tom,

Most of my commute to work at night is on for the most part a good stretch of level highway. Without a doubt I know that when I am traveling 62-65mph it will go up, then go down. It will do this many many times. My ultragauge would tell me that my RPMs would be at 2200rpm, but then when it would drop it would go up to 2500rpms. And just as you mentioned earlier, if I give more/less gas the problem goes away. On RARE occasions the rpms would not fluctuate during the course of a drive to/from work.

Just got an update from UPS that they are delivering my TPS sensor today so I can update later tonight after I replace it! I have noticed also that when the RPMS don't fluctuate like that my gas mileage is quite a bit better by almost 3-5mpg, which isn't a ton but considering it could take me from about 24mpg to almost 30 that's pretty decent.

Thanks,
-Nigel

NewShockerGuy · #6 05-17-2017, 08:02 PM

Tom,

Just an update.
Got the new TPS sensor. It is the correct one and matches exactly what I have. One thing I immediately noticed. My TPS sensor (where the attached image and the arrow is pointing to the center piece that the throttle body rod goes into the TPS sensor) I can move that center piece with my finger back and forth about 180 degrees. There is no resistance at all. With the new TPS sensor I am unable to move it at all with my finger.

I changed it, super easy with the two torx screws. When I drove to work today the RPM's didn't jump around like it has been for years. At about 60mph I'm right at around 2100rpms. Compare that to it jumping to and from 2100-2500 previously all the time.

I can't wait to see what my gas mileage is going to be next tank!

Side question but since this jump in rpms has been going on for a while do you think damage has been done to the tranny? I honestly thought my tranny/tires were just not happy with it trying to go up/down a gear when cruising on the highway...sooooo annoying. Even more annoying is me not asking this damn question years ago! Glad you posted honestly, everything else I have read everyone just kept saying it's the larger tires that was causing it, but now I know that was not the case at all.

MUCH APPRECIATED! :-)

-Nigel

NewShockerGuy · #7 05-31-2017, 09:03 PM

Figured I'd update after a week or two of driving.

My RPM's that were jumping all around is no longer happening! Feels like a different truck from it not doing it honestly. I wish I would have asked this damn question years ago as I would have changed out the sensor then...lol Oh well.

:-)

-Nigel