Dead Pedal - Code P0121

[Tractorman]

Just wanted to share a dead pedal experience.

One March 19, 2018, during  a return trip from Crescent City pulling my travel trailer, I exerienced the dead pedal syndrome about fifteen times in the last 35 miles to home.  Each event lasted about 20 seconds (sometimes longer).   It was a slow 35 miles, but the truck made it home.

 

At this time the truck had logged a total of 289,000 miles with 202,000 miles on the VP44.  The check engine light came on and stayed on and code P0121 ( Accelerator Position Sensor Signal Voltage Too Low) was set.

 

I was hoping that I could replace the APPS and the problem would be resolved.  I went on-line to Blue Chip Diesel for help.  I was immediately disillusioned when I read the following:

 

“The symptom of Dead Pedal is rarely caused by the APPS (Accelerator Pedal Position aka Throttle Position Sensor) and 90% of the time it is caused by a faulty computer on the top of VP44 Injection Pump. These numbers are NOT an exaggeration.”

My old analog voltmeter doesn’t work anymore, so no testing of the APPS.  I decided to replace the APPS with a Timbo since the original had logged 289,000 miiles.

The good news is that I have driven over 3,000 miles (mostly towing) and the dead pedal condition has never returned and no codes have been set.  The engine runs strong.   Only time will tell if replacing the APPS was the correct solution.  I will post again if I the dead pedal condition returns.

 - John

[dripley]

Good to hear. The episodes of dead pedal I have experienced were neither the apps nor the VP. Electronics drive me crazy.

[Mopar1973Man]

1 hour ago, Tractorman said:

“The symptom of Dead Pedal is rarely caused by the APPS (Accelerator Pedal Position aka Throttle Position Sensor) and 90% of the time it is caused by a faulty computer on the top of VP44 Injection Pump. These numbers are NOT an exaggeration.”

 

Hype...

 

Typically when the P0121, P0122 or P0123 code is present with the "Dead Pedal" its going to be APPS sensor issue. The bast way to test is to have a live data tool and data log both Engine Load and the APPS sensor together in graph form. The engine load reports the amount of fuel given to the engine. So if the APPS and the Engine Load drop together its a APPS sensor issue. If the APPS sensor stays high and the engine load drops then it could be an ECM issue. 

[Dieselfuture]

Can't believe everything that everyone is saying. Glad you got it fixed.