Engine/Transmission (1998.5 - 2002) APPS closed throttle switch... adjustable?

[ERuhl]

Sometimes my exhaust brake comes on, and sometimes it doesn't. The switch is operating right on the edge. The last time this happened the APPS was replaced under warranty and now it's happening again. It used to take slight movement of the the throttle for the brake to disengage, and now just touching the pedal turns it off (assuming it was able to come on to begin with). I don't want to replace the APPS just for this, but I need my exhaust brake to work. Does anyone know if you can adjust the closed-throttle switch?

 

[Bob4x4]

There are 2 idle validation switches built in to the apps. One is open at idle and the other is closed at idle. When you come off idle they change states. There is no adjusting these. Connect a scanner and watch the states of the sw's to learn if they are your issue. I doubt it if you do not have a mil on,they are monitored.



Bob

 

[ERuhl]

Right, what I'm suspecting is that at least one of them is barely being triggered when I let off the throttle. The slightest pressure on the throttle turns off the brake. When they first installed the replacement apps you could touch the throttle pedal, but the brake wouldn't go off until you actually moved the pedal. Now if you practically breathe on it the brake turns off. Are the idle validation switches visible with the APPS cover off or are they internal to the APPS mechanism itself? I looked in the FSM and find only references to the two switches, but no diagrams showing their location.

 

[ERuhl]

Well apparently my APPS is just dieing. This morning the e-brake stopped working halfway to work, as usual, however the idle went up to 1200rpm. Shortly thereafter the CEL came on and the throttle response went completely dead. On the bright side, at least the idle went back to the stock 750-ish. Pulled to the side of the road and checked codes, 121 & 122 both of which point to the apps. Lovely. I started it again and it lasted the rest of the way to work, but now I know the APPS is indeed dieing a quick death. This is my second one, the first was replaced under warranty with the same e-brake symptoms. Am I the only one with an APPS life expectancy of ~50k miles?

 

[ERuhl]

Fwiw Cummins has these on 4-6 weeks backorder for $390. I found one at a local dealer for $375. The truck just turned 100k miles this weekend, what a way to commemorate the occasion

 

[rweis]

I can not say good, bad, or indifferent, but I wonder if because Gary and I blow OAT on the VP44 virtually all the time the engine is running and for 1 1/2 hours after shutdown and the blower air also dumps into the APPS, if that helps cool the APPS and will be a side effect of prolonging its life?



I have 84k now and have done the Bill K reset procedure once about a year or so ago.



Bob Weis

 

[ERuhl]

I noticed it is rather toasty in that area when I was replacing the APPS (fortunately that's a pretty quick and easy task). When I was changing it out I was wondering if heat was a contributor. I thought an insulator block between the bracket and the APPS assembly would reduce the conducted heat, but didn't consider the hot air in the engine bay. Heat is supposedly the source of failures in the VP44 electronics so it wouldn't surprise me if that's what is killing the APPS as well. $405 later (after taxes) mine is back to normal... for now.

 

[rweis]

The blower is $40 and last about 1 year (20k miles). I have no idea if it is a player or not, I use it mainly to cool the VP44.



MIGHT (and of course MIGHT NOT) be good insurance though.



I thermally protect the VP44, might reconsider (for $400 for a APPS) to also thermal wrap the APPS and provide the same OAT to it. Interesting.



Bob Weis