I have had intermittent problems with my accelerator pedal position sensor for a few years now and need some advice as to what is causing the problem. My 2004 3500 5.9 has the APPS located under the driver's battery tray and for some reason keeps my Check Engine Light on most of the time. I just replaced the apps yesterday 5-24-2011, cleared the CEL and then today the CEL came back on and the truck was throwing the same P2121 code. Why would the truck do this? Before I changed the APPS, I would get no pedal response, over acceleration and other strange things. With the new APPS I just get the code and the CEL. Is there another sensor or something that I need to change? I replaced the rail pressure sensor about eight months ago and don't have the truck modified. Could the ECM be faulty? Please help!!

 

read up on my problems with it

could be something as simple as a ground, to something in your trans if its an auto, judging from your description, your truck is a 6 speed. I would also check the fan clutch, the wiring, the grounds, and connections to the pcm..

 

Not sure if it's still around or even available but do a search for the Timbo APPS fix. From what I've read it's a dead fix for most any APPS problem. Very reasonable on price as well.....that is, if it's still around!!!

 

My truck is the six speed manual. I forgot to add that I have also had trouble with the batteries randomly going dead. Might not do it for six months or a year, then all of a sudden it will kill batteries for weeks. I have looked at the timbo fix and as far as I can tell, that APPS will not fit my truck as my APPS switch is under the driver's battery and a different model altogether. I just checked the ground strap on the back of the engine and it looks ok. Where is the PCM located? All other wires look intact, but I have no way of checking voltage.

 

Could it be the Fuel Control Actuator or the Cascade Overflow Valve????

 

Having just went through this on a 2006 I would suggest resetting the codes with a scanner. I replaced the peddle APPS and it acted the same. Battery disconnect did not get rid of p2121. Hard reset with scanner did the trick. Only stumbled on this because I was monitoring the APPS voltages with the scanner and could see no abnormal voltages after changing APPS. Decided to clear the codes.

 

ecm is on the left side of the block.

that thing with three connections to it, might wanna check connections to it.. and as stated, resetting the apps, and battery disconect do not always work.. i would try what DGURU stated and reset the ecm with a starscan, and get rid of the trouble codes..

make sure you also check the wires to the fan clutch, and all grounds, make sure they are loomed, tight, clean and not making any unnessesery contact with anything. those lil ****** can cause alot of headache.

if your batteries are being killed, it might be a ground or a short killing them as well.. again, goes back to the grounds.. or a faulty connection somewhere..

does your truck throw any other codes besides the 2121? or similar?

IE 0483, 2122,?

any other codes could also cause the apps to act up... and again, it was similar factors with mine.. multi actually

 

I cleared the codes with my scanner a few days ago and they have not come back. Drove the truck about 250 miles yesterday and no issues. I will check the ecm wires. No other codes have been thrown, yet...

 

Wow some good reading, since I am having the same issue. All intermittent, weeks/months apart, 2121, 2122 with zero pedal. All only when towing my 9k lb tractor on the interstate. It would go into limp mode and could still go 20 mph. Each time was a BANG cruise control kicks off, and no pedal. Very scary. I have reset three times so I fugure its a real problem. Guess I will start checking as posted above. I assume the APPS has some sort of troubleshooting or +/- tolerance?

 

Had similar problem in my truck, no accelarator response on startup after driving awhile then stopping. Tried numerous things, mine has power pedals-found problem worse when pedals full away-lubed cable profusely with WD40 and worked pedal adj. several 10's of times. Now leave pedals at about 3/4 away from driver and keep cable lubed-no more problems in about
35k. Keeping fingers crossed. Good luck with yours.
Never did get code/CEL.

 

Well this is a learning curve, my truck is an 04, not 04.5 since the apps is located on the motor and not the pedal. A little knowledge goes far. I will try checking all the grounds and wires, clear the codes once more, do the APPS reset and if it comes back again, im gonna order Timbos deal. I dont want to steal the thread, but also getting DTCs

P0587 (Cruise Ctrl Vent Ctrl Circ Low)
P2607 (Intake Air Heater Relay 2), along with
P2122 Throttle/Pedal Pos Sens/Switch D Circ Low Inputi,
P2121 Throttle/Pedal Pos Sens/Switch D Circ Range/Perf.

Just wondering if these are related to each other, been reading about funky grounds and altenator issues causing wierd things. I did see some serious corrosion on the driver side batt terminals, but thats about all.

 

04.5 still have apps on the motor or under the driver side battery. Mine is on the motor and it is an 04.5

 

well **** im all confused now, my buddys 05 is not located on the motor, just a big empty spot. We compared side by side yesterday, I was told my truck was 04.5 but the motor mounted APPS Replacement parts, are for the 98-04. 04.5 and up dont have the plastic cover / motor mounted APPS acording to Timbos parts site and a few others. The only thing under the drivers side tray on mine is a cruise control servo, thats the first place I tore into, then decided to do some more research. So how else can I tell if it is 04.5 or not?

 

I was told that if it has an Id sticker on the drivers side valve cover instead of the riveted plate on the front of the motor it was an 04.5 Any truth to that?

 

I have a 4.5 and the motor mounted APPS. Also I have a sticker on the drivers side valve cover stating the 325/600 engine.