5.9L Cummins APPS Replacement

How to Replace the APPS, Fix Dead Pedal Condition

5.9L Cummins owners experiencing a "dead pedal" condition (unresponsive accelerator pedal) most likely have a faulty APPS; accelerator pedal position sensor. This is also sometimes referred to as a TPS (throttle position sensor) since most code readers do not distinguish between an APPS (for diesels) and a TPS (typically for gassers). Replacing the APPS is a relatively straight forward procedure that will take most mechanically inclined individuals about 30 minutes to complete. When the APPS fails, it is common for the check engine light to illuminate and trigger a DTC P2121.

The following procedures are specific to the 1998.5 to 2003 24 valve Cummins and some 2004 models.

Click any thumbnail image to view fullsize

• Locate the APPS cover on the front, right of the cylinder head (standing at the nose of the truck and looking at the engine). Remove the black cover.

• Six 10mm headed bolts hold the bellcrank/APPS assembly in place. Remove the bolts and the assembly to expose the APPS

• Once you have located the APPS (on the back of the bellcrank assembly), remove it using a T20 Torx. The screws use loctite and may be difficult - be careful not to strip the bolt heads.

• With the old sensor removed, install the new APPS. Notice the the slot on the APPS must engage the tang on the bellcrank shaft. Make sure to line up the slot into the tang when installing. If the APPS does not mount flush with the surface, the slot is not installed into the tang properly. When the slot/tang are engaged properly, you'll have to rotate the APPS clockwise to line up the mounting holes. The mounting holes on the APPS are slotted; it is recommended that you twist the sensor clockwise as much as possible before tightening.

• Reconnect the sensor connector, then remount the bellcrank assembly.

• Insert the positive lead of a digital voltmeter/multimeter into pin #3 (green wire) of the factory sensor and negative lead to negative battery terminal/good ground. If you do not have a spade to do so, you can use a section of thin copper wire to slide in the back of the connector, and then attach your meter to that. We do not recommend stabbing the back of the connector with the thick pins that most meters have, as this can mangle the wire in the connector.

• With your meter on low voltage DC, start the truck. At idle, the voltage should read between 0.580 - 0.670. Locate the idle stop screw and turn it clockwise until you see voltage begin to rise, then back it off half a turn.

• Disconnect the volt/multimeter and reinstall the APPS cover.

• Location of the idle adjustment screw is marked by the red arrow in the fullsize image.