P2121 P2122 P2123 no throttle response - Dodge Cummins Diesel Forum

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Old 11-07-2007, 06:30 PM   #1 (permalink)
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P2121 P2122 P2123 no throttle response

Have a 2003 6spd 2500. From day one, the truck had that irritating rough running at cruise speed. Finally, it became so bad the truck was unsafe to drive (like 70mph bumper to bumper, hit the gas, no body home...).

I did searches all over the internet. No direct "hits" on P2122 (the common error code mine threw). APPS low. My truck's problem seemed to stem from the accelerator pedal position sensor (APPS). Oddly, at the last there, the truck would only run smoothly with the cruise control ON (yes, ON).

I found out the replacement sensor was in the neighborhood of $700 from Dodge, and I wasn't about to drain my bank account on a 'hunch'. This is what I did TO FIX MY TRUCK.

I found the APPS setting procedure on another forum. I bought a digital voltmeter first. Key on, engine off, I checked the output from the APPS sensor plug, using the yellow wire as "+" and the battery ground as "-". I saw .52 volts. The tag on the APPS said 0.535 volts. Easy enough to change: the APPS has 2 locktited Torks bolts, very fragile, but with deliberation, I was able to loosen them, and readjust the APPS to .54. Cleared the trouble codes, pushed the gas to the floor (key on engine off) and let off, turned the key off and on, started it up, and went out for a drive.

And it ran well. For the first, oh, 10 miles or so. Then the truck started running rough again, like it was trying to defuel or something, at 45mph, and then the check engine light lit, the throttle pedal went dead for about 5 seconds, then it "woke up", but still ran rough, like a mind of its own.

Trouble codes P2121, P2122, P2123 again. All pointed to a bad APPS.

I disconnected my Banks 6 gun and reset my Rokk sensor to stock timing, cleared the codes, and tried again. To no avail. The rough running wasn't as rough, but it still threw the codes, the pedal died and came back, same ol thing.

I read somewhere on the internet about noise on the APPS signal and how somebody put a capacitor inline and fixed theirs; however, I lost that link in the meantime, and ended up being inventive.....

Went to Radio Shack. Bought a 220 uf capacitor with no polarity, and a soldering gun kit, spent $10. Back at the truck, I unplugged the APPS wiring harness from the APPS. There are 6 wires. The power comes from the yellow one, and I found the green with orange tracer is 'ground'. I put the capacitor across those 2 wires, buttoned it up, cleared the codes, and tried again.

It has not thrown a code since. Not even a hiccup. Runs really really well. The only drawback I found is that the pedal input has like a subsecond lag to it now. So, if I go to shift like I used to (depress the clutch at the same time I let up on the gas), the engine revs a bit (kinda like the Banks at level 6). I had to relearn how to shift!

Now I let completely off the gas. When I anticipate the audible 'kick' sound from the gas pedal, I begin to engage the clutch. No extra reving. In traffic, the truck feels like it has a lot of extra punch, mostly due to the induced lag now from the capacitor, I guess.

Maybe I should try a 100uf. But hey,....

I just saved myself a $700 repair bill for $10.

Hope this helps anybody frustrated with rough running of their 3rd gen.
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Old 11-08-2007, 04:46 PM   #2 (permalink)
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Thank's for the info. spinlocker. :thumbsup
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Old 03-12-2009, 07:53 PM   #3 (permalink)
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As time has passed.....

The lag reappeared. I found a procedure where you drill a hole in the APPS and inject plain ol layin around electrical cleaner. This also worked just fine. I don't know exactly where the procedure is found or which forum, but it does exist.
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Old 03-12-2009, 07:54 PM   #4 (permalink)
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Ah, here it is.....

Anatomy of an APPS - TDR Roundtable
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