Hi everyone, I'm fairly new hear and suddenly have been having some TPS DTC woes. My vehicle is a 2006 Navigator (5.4 3v Triton motor) and there doesn't seem to be anyone in that section of the forum horribly familiar with my problem, so I was hoping maybe someone on the F-150 side might be able to chime in since it's the same engine.

It all started after I replaced my oil pump, timing chain (and tensioners, guides, crank sprocket), cam phasers, cam position sensors (Motorcraft) crank position sensor (Motorcraft), VCT sensors, and spark plugs.... and then also cleaned my MAF and throttle body. During this time I replaced all front accessories just because I didn't feel like putting 130k mile parts back on for them to only last who knows how much longer. Drove the truck for a few weeks and everything was totally fine like before, aside from the new power steering pump that was defective. No DTC's though. I replaced the power steering pump with another new pump, and all of the sudden I started having drivability issues. The truck was having trouble accelerating and then I found I was getting TPS codes and the engine went into failsafe mode. I shut the engine off, starting it back up, and no more fail safe mode- though the car was still hiccuping on acceleration some here and there.

I've been troubleshooting this issue on afternoons and weekends here and there for a couple of weeks now, and have found myself in a black hole of reading TPS voltage. With the KOEO, pressing the accelerator pedal doesn't open the throttle enough to check that the TP1 and TP2 voltages are within spec while monitoring the PID's using the FORScan app on ,my smartphone. This is likely due to the P2104 and P2106 limiting how much voltage the electronic throttle body receives. Every time I clear the codes, turn the ignition off, and turn it back on again the codes immediately come back. The engine doesn't have to be running for the codes to immediately re-appear, immediately limiting the range of motion on the throttle body blade. So using the Ford PC/ED for codes P0121 and P0122 hasn't been that useful for my scenario.

So I removed the upped intake manifold and back-probed the TP1 and TP2 wires at the TPS connector and read the voltage with my digital multimeter. Using the DMM, both wires are within spec at both closed throttle and full throttle. However, if I monitor the PID's while opening the throttle blade by hand the TP2 wire is only seeing 3.52 volts at full throttle (but shows 3.82 on the PID... still low) instead of 4.1-4.8. The rest of the PID's (TP1 @ no throttle, TP1 @ full throttle, TP2 @ no throttle) show slightly lower voltage than my DMM shows, but those 3 are still within range. But the P0121 and P0122 codes pertain to circuit "A" anyway, which I assume is TP1, which is within voltage range regardless of whether I look at PID's or use the DMM when I manipulate the TB by hand.

Other troubleshooting I've done:

I've manually sent 5v to the throttle body and it fully opens without issue. I replaced the electronic part of the throttle body regardless and no joy.

I've checked the TPS thoroughly using the PC/ED troubleshooting...... no shorts, resistance between pins is where it should be.... but I replaced it anyway and still no luck.

I've checked the wiring between the TPS connector and the PCM harness and there is no resistance, no short to ground, no short to power, no short between the wires. Wiggling the wiring at the PCM and the TPS connector had no impact on the DMM readings.

I back-probed TP1 and TP2 wires at the PCM and as I manipulated the throttle body the voltages on the DMM show the same as probing at the TPS connector. So the proper voltages are making it back to the PCM.

The accelerator pedal position sensor-- I don't have a PC/ED for that on what the voltages and resistances should be. Looking at the PID's I'm seeing voltage on each of the 3 potentiometers on the pedal, but not sure if they are within spec of if they would/could even be part of the problem. Someone has mentioned to me that P0121 and P0122 have nothing to do with the accelerator pedal, but since all TPS stuff is checking out and since the description of the codes on my FORscan app have the word "throttle/pedal" in them.... I'm not sure I should rule that out.

Here is a video I shot yesterday of the accelerator pedal position sensor and TPS PID's. Notice the voltage on the TP1 PID stuck at .03 at closed throttle and .02 at full throttle. Even though the throttle range is limited with P2104 and P2106, the TP2 PID is showing plenty of fluctuation versus the PID for TP1. Why is the computer seeing less voltage than it should after all of the above that I have done???


Any help on this would be HUGELY appreciated... this has consumed so much of my time and I have gotten nowhere with finding the problem. I suspect a bad PCM or bad accelerator pedal at this point, but would like to confirm that before replacing either because neither are under $300. Still weird how all of this came about out of nowhere after replacing the power steering pump a second time. Thanks everyone!

-Andrew

 

Prob a bad throttle body. Even to this day Ford is having issues with them.

 

Thanks for the response! But yeah I did test the throttle body by manually feeding it 5 volts and it went to wide open throttle without issue with KOEO. I replaced the electronic part of the throttle body anyway (nothing mechanically wrong with it.... it's very clean and in great shape, and the gears operate smoothly) and still the same results. The reason the throttle won't open all the way with the accelerator pedal is because it is only getting 1.2 volts into it, likely because of the PCM failsafe mode, which restricts the amount of voltage the throttle body gets, which in turn restricts how much the throttle blade will and won't open.

The PCM is recognizing a voltage discrepancy as soon as the key turns to the ON position, and prevents the throttle body from opening above idle.

 

You could try doing a loaded voltage drop test on the wiring between the PCM and TPS. Resistance checks are useless on wiring. Could also have poor pin fit on one of the circuits. If all that is good I would suspect the PCM before the pedal.

 

This is now your third separate thread on this vehicle for the same problem.

It's far more effective if everything is in a single thread.

 

I mean, I'm not being rude but things are changing between threads. Yes, they are all regarding DTC codes for the same vehicle, but no longer having some of the same problems as originally reported, and finding newer problems and starting a new thread about this with a currently-accurate title has been more likely to get more help in the past when I've had to resort to this method on other forums in the past, when the initial thread received very little attention.

I posted here in the F-150 section today because I had no idea how few people were going to be able to help in the Expedition/Navigator section, and seeing how much more lively this section is, along with changes in the problems..... here I am. I think we all know what happens when you use one thread and no one responds to it... it slowly makes it's way off page 1 and disappears. Just trying to actively get some help here and you were one of the very few to offer help, which I really appreciate, but I'm just getting desperate and need to fix this issue like 2 weeks ago. Sorry if this comes off as a rant-- it's not.... I'm just frustrated about trying to get this figured out.

Got my PC/ED DVD in the mail today, then found out I now lost voltage to the TAC+ wire that I last had voltage at a couple days ago. I checked for resistance and the wire is broken somewhere. Thought that was a degrading wire causing this problem all along and it finally gave.... but I jumpered a new wire from the PCM (pin E34) to the pin 1 on the TAC connector and got the throttle working again but P0121, P0122, and P2106 keep coming back as soon as I clear them. Voltage from the PCM to the TAC+ wire still isn't where it needs to be, probably because of 3 DTC's, which all limit voltage to the throttle.

Following the PC/ED again I'm at the point of after testing all the TPS wiring and the sensor yet again I need to take the vehicle for a drive and compare TP2 voltage to load percent. Well, I can't take the car for a drive because it won't accelerate worth a darn, even gently, so I can't do the test. Black hole. Very frustrating. Want to drive this truck off a cliff, but I'd have to push it to one, and probably have to push it off of said cliff.

Cliff Notes: TPS circuit "A" not getting enough voltage; throttle body won't receive enough voltage to open the throttle blade, which would in turn allow me to test the TPS without human interference. Enter black hole.