APPS/Bellcrank and Pacbrake problem HELP!!

[befrazier]

I have had some trouble with code p2121 (APPS) for some time now. It finally gave out and I have no pedal or all pedal, nothing in between. I found (on back order) and replaced the APPS that is under the battery and the truck ran great down the road and back. I started the truck approximately 3 times to get the engine light to go off. I started the truck again and at idle I turned the exhaust brake on and instantly the engine light came on and no pedal again. The codes that I had before I changed out the APPS were p2121, p2127, p0483 and p0477. The new APPS has some throttle in the middle but it is definitely not right. The truck has 112k on it and this is the second one that I have bought. The first one went out at 80k and I did not have the Pacbrake on at this time, I put it on a couple of months later. The Pacbrake has been on for 2 years now and the APPS has been on for 2 years and 4 months. Pacbrake said that they have never heard of anything like this and believe that there should be nothing with there system that would have caused this. I think there could be because the brake comes on when you let off of the pedal and goes of when you push it. A buddy came over and cleared the codes but I now have P2121, P2122 and P2127. Just wondering if anybody can help me out there, this part is hard to get and I don't have another at this point. Not sure if this last one that I bought is bad or not, now. Any help to diagnosis this problem would be greatly appreciated, this thing is driving me nuts.



Thanks in advance,

Brian

 

[jelag]

I sold and installed PacBrake for 20 years... . and owned many trucks over the years with PacBrakes on them... all were connected to the ECM... . if the PacBrake is doing something to effect what is happening its because you've got the wiring for the PacBrake in the wrong connectors on the ECM or have supplied 12V dc to one of those pins at the ECM... those are the only 2 actions that would cause some interference to the ECM... .



I would personally go to the ECM and remove the 2 pins from the ECM that go to the PacBrake system... . One pin does nothing more than go to the PacBrake switch, and than to ground... . so when the switch is on, a path to ground is complete for the ECM to know you want the PacBrake to turn on... the other pin is a path from the relay, the ground side..... and the ECM grounds the relay, and turns it on... thus applying power to the solenoid and air to the PacBrake to turn it on... only current from the coil on the relay should go through the ECM to ground...



TO REMOVE these pins you have to remove the connector to the ECM and use a tool to compress the locks on the pin, which allows you to push them out of the cavity...



If the problem clears up... than you have a wiring problem in the PacBrake and that needs to be fixed/repaired... if the problem doesn't clear up... the problem is no the PacBrake...

 

[befrazier]

Jim,



First of all, thanks for the response. I was hoping that I would get a response from someone that knows and understands exactly how the Pacbrake works. I have spoken to you before when I was in the market for the Pacbrake. I don't remember, but I may have even bought it from you.



Is there a specific tool to remove the pin or do recommend something that will be suitable? After I remove the pins do I need to replace the small plastic pieces that came out of the pin hole? I am real sure that this APPS went bad when I turned the switch to "ON" for the Pacbrake, so it sounds like I may somehow be getting 12v through one of these two wires. I will have to remove the wires and test it out. How many volts should I get through each of these wires?



Thanks again,

Brian

 

[Prairie Dog]

I have had the Pac brake relay freeze up and hold the ECM connection low, all it does is throw a code. It has no effect on the apps.

 

[befrazier]

OK, here is what has happened. I called Pacbrake again and they assured me that there is no way that it could be affecting the APPS. They recommended that I cut the wires from the ECM and splice them together (the black and white), this would take it out of the picture and the pacbrake would work manually by turning the switch on and off. I believe that I have had a bad connection again at the APPS, these connecters suck, I cleaned and reconnected again and zip tied the plug up snug. I have not experienced any problems at this time. I deleted the codes but I still have one code that I cannot delete (PO477 Exhaust Pressure Control Relay Low). I believe that I have read that this code deals with a exhaust brake, but I have no idea what it means. Where is the relay? Is it bad? So on so forth. I had this code before I cut and spliced the wires but still have the code. The truck runs good and the exhaust brake works good manually now.

Any input on the p0477 code would be appreciated. I would like to be able to delete the code and not have any show up when I cycle the key.

Thanks, Brian

 

[Prairie Dog]

Thats the code mine threw when the PB froze and forced it to go low. It sounds like your ECM's output for the EB is now stuck low and I think it's because you spliced the wires from the ECM together. I don't understand why they said to do that but I would disconnect them as they would be if you had no EB and I suspect your code will go away after that.
If you can't clear the code after that then I would disconnect the batterys for 30 minutes or more and hope that allows it to reset but that may not do it either.
Connecting the wires together may have destroyed the digital IC that provides the Low for the brake.

 

[RVTRKN]

befrazier, even though its after the fact, I would follow jelags advise first, before you jump the ecm wires together. That way it would confirm one way or the other if indeed it is the PacBrake. Hopfuly you didn't spilce before the factory plug, keeping the wire harness virgin.

 

[befrazier]

Prairie Dog,

I had this code when the EB was connected to the ECM and also after I cut the wires and spliced them together. The wires that are coming out of the ECM are not spliced together they are taped up individually and zip tied out of the way for now. I can always go back and splice them back together if I want to, I left plenty of room. The EB works only when I flip the switch on my gear shifter to ON and turns off when I flip the switch to OFF. I believe the Pacbrake guy told me that you can only do this on a manual shift. I don't think that the ECM even thinks that I have an EB at this time, unless those wires just being plugged in, makes it think that there is an EB there. I could not get the wires out of the ECM. I have had the batteries unplugged a few times and the code keeps coming back. ???????? Maybe I should call Pacbrake again and ask them why the code will not go away.



The truck is running great at this point but I still have one question. I am not sure if any of the 2 APPS units that I have on the shelf are bad. Is there a way to test these units to see if they are good. I believe that the bad connection at the APPS unit plug has really cost me some money, but not sure. I don't want to install them on the truck to test them, the truck might break again. LOL

 

[Prairie Dog]

The ECM doesn't know there's an EB on the truck. When ever the throttle has been at zero for a few seconds the ECM just supplies a ground (or a digital low) for the EB relay if one is present. That same pin would go "low" even if nothing was connected to it. The ECM will throw a code if that pin is shorted though.
Running the EB without the ECM or something telling it when to engage is fine as long as you remember to turn it off when you take off.

Did you calibrate the APPS after installing it?

 

[befrazier]

Prairie Dog,



When I first installed it, it worked perfect. It was when I switched the EB to ON with a cold engine, that the engine light came on and the APPS had no response, unless put to the floor and then very slow acceleration. I tried the calibration after this happened with no luck. After days of messing with the truck I did the calibration 3 times before it took and now it is running great. I have also tried the calibration on both of the other APPS's with no luck also, but now I don't want to put them on the truck to try again since it is running good.



Where is the pin that may be shorted? In the ECM, APPS or in a relay? How can it be fixed, if this is what it is?



Thanks, Brian

 

[Prairie Dog]

Sorry to confuse - it doesn't sound like anything is shorted since you just taped those wires off. Hopefully someone like Sag2 will chime in here with some ideas.

 

[befrazier]

I am taking the truck to the dealer for a recall on the front end this Friday. I was considering letting them diagnose this code but if anybody has any more thoughts on this I would like to save my money. I don't think that this code is a big issue, I would just like to get it taken care of if possible. I would also like to know if there is a way to test out the extra APPS's that I have, they may be good.



Thanks again, Brian

 

[jelag]

once you cut the wires to the pins on the ECM the computer has no way of knowing there is something there... . UNLESS one of those pins is bent and touching a second socket in the ECM, that was why I first suggested removing them... if you pull the plug from the ECM you can pull the pins out from the pin side if you cut them close to the connector on the outside... pacbrake has them available as repair pins... . if these pins are not bent and connected correctly in the ECM, and are cut wires outside the connector this is no, and can not be your problem... . move on to correctly diagnose the problem...

Like I said earlier... . one pin when grounded will tell the ECM that an exhaust brake is installed and should be turned on or off by the computer... . so one pin used to go to the switch... and to ground... if this connection had any other path to 12V DC than all bets are off... Again... . if 12 VDC has been applied to either of these 2 connections there is a chance that the ECM could be damaged... . this is a path to ground only...

The other pin is a ground path for a relay that will cycle the solenoid and turn the butterfly on/off based on engine conditions... based your ECM Programing...

If you think about this... . the ECM connects the two pins together internally so that when the ECM wants the brake on, it closes the circuit and if your switch is turned on (read a path to ground) the circuit is complete and the brake comes on... .

I hope this adds clarity for you. .

 

[befrazier]

Jim,



I tried to remove the wires as you suggested with no luck. I also visually inspected the plug and the internal pins at the ECM and did not notice any damage. When I initially installed the wires into the ECM 2 years ago, I did have troubles get the white wire into the plug on the ECM. The wire is not stiff enough and kept bending as I pushed the end in. At one point about a month later the ECM spit the white wire out, so I had to reinstall the wire and it has held ever since. I don't know if I would be able to push the wire all the way through the plug with it being so flimsy (bendable). Also the hole on the backside of the plug looks pretty small to me, for the wire to come all the way through the plug, but it may. I would hate to get the pin/wire stuck and not be able to get it through and then not be able to reconnect the plug to the ECM. Then it would really not run. LOL



I believe that the EB was working as it should, before I cut the wires and spliced them together. I thought that there was something in the EB system causing the APPS to fail. It may have been a total coincidence that when I flipped the EB to ON, the engine light came on and the APPS failed to work. I do not have an engine light with the P0477 code and everything is still working and running great. I do have to remember to turn the EB OFF before I accelerate at this point. I would like to splice the wires back to Pacbrake specs at some point, just in case someone else drives the truck. At this point it is my truck to drive and nobody else. I do not want damage caused by non-experienced EB drivers that may accidentally flip the switch.



I hope that I am following your suggestions correctly, if not please try me again.



Thanks, Brian

 

[Prairie Dog]

There's a special little tool for installing and removing those pins. It probably cost less than a dollar and it would sure be nice if it was included in EB kits.

 

[befrazier]

I talked to timmbo apps guy and he made me a new pigtail plug that plugs into the apps sensor under the battery box. I had a guy take the old plug off and install the new plug. He noticed on the old plug that there were two pins loose inside of it. The truck runs great now. Any of the trucks that have the apps under the battery and is having the reoccurring codes may need to check this out. I have had this issue for several years and have bought two sensors with the same problem coming back. I had the guy check out the older apps sensors and they both worked fine. Hopefully this long process, trial and error, determination and the help from TDR and timmbo apps my problems are gone.

 

[Prairie Dog]

Thanks for the update and I'm glad you got her figured out.

Scott

 

[befrazier]

The APPS problem came back a couple of months after the pigtail replacement. Although I needed to replace the pigtail anyhow. I unplugged the two big electric plugs attached to the firewall on the drivers side, cleaned with electronic cleaner and put dielectric grease on every small pin hole and plugged back in. I was reluctant to post for quite some time after I did this because of the past failures. I have not had any problems for approximately 9 to 10 months now. Hope this may help someone.