Engine/Transmission (1998.5 - 2002) ECM pin #20 activation

[Heetseeker_1]

I was putting in a pac brake in my "new" truck the other day and wired the electrical harness into the pcm as instructions stated. I double checked all of the wiring and the brake still will not activate. As it turns out, where I plugged in to the PCM (pin #20), does not send a 12v signal to the solenoid. I called PacBrake and they said that the rpm has to be over 900 for the 12v to turn on... Revved her up = Nothing. Called PacBrake back and they said that some times that pin on the ECM isn't activated and you have to have it done by cummins.



Has anyone else experienced this? I'm going to look into a microswitch on the throttle as an alternate method of getting this brake going. At least i'll be able to warm the truck faster at an idle that way.



Steve.

 

[Whitmore]

Steve

I am a little confussed at this point, it is my understanding that pin #20 will not activate a 12v signat unless you are off the throttle and the pcm see's that no fuel is being delivered, so at this point I am wondering why they tell you about this 900 rpm thing



As far as pin #20 not being activated I am not sure if this is a re-flash thing or not.



I have installed 3 Jacobs brakes on 24v Cummins now and pin #20 worked every time, on 1 of the rigs it took me 2 tries to get contact but it worked then.



cheers, Kevin

 

[klenger]

Are you sure you have a good connection to the ECM?



Here is the part I bought from Cummins to make the connection.

 

[Heetseeker_1]

Sorry, I wasn't clear. The ECM won't send a 12v signal under 900rpm. I was told this because when I was troubleshooting the setup, the truck was at idle. The tech told me to rev it up past 900rpms and let off to activate the brake. So, if what he said was true, the brake would automatically turn off below that rpm point, right?



I'll mess around with the connection tomorrow. Maybe I didn't push the wire into the harness completely. (I hope it's that simple)



Steve.

 

[Thomas]

Pin #20 was not active on some of the earliest ECM's (maybe 1998. 5?), requiring a reflash. I think this information was included with the E-brake by Jacobs I installed on my model year 2000 Ram.



Pin #20 is active anytime that the engine has been unfueled more than about 1. 5 seconds, regardless of engine speed.



Time to talk to another tech!



I second klenger's thoughts.

 

[Heetseeker_1]

Got it! Bad connection at the ECM. I took the filter housing bolts off, moved the filter down so I could access the wire and pushed it in and gave it a couple of twists. That did the trick. Thanks for the help.



Steve.



BTW, we have activation at idle...