More diagnosing

[rgwilliams]

According to this page, although it applies to DDEC 3, the ECM has to be enabled by a DD dealer mainframe before the jakes can be used by the ECM.  See 7.1.5 or page 4
Maybe this might help

Rob Williams



http://www.dmbruss.com/images/Schematics/DDEC/7_DDEC_ECM_Software_Features.pdf

[NJT 5573]

Jakes use oil to hold the exhaust valves open. If they have not been used for a while they bleed off and need to be reprimed by dropping off a hill with them on to pump some oil into them. The equivalent in a shop would be hard to achieve.(Not real real hard)! Jakes have overrides and won't work except with the throttle closed under compression carrying some speed.

[Sammy]

Ace, you should hook up a Pro Link and look at the I/O's (Inputs and Outputs) of your ECM.
Take it for a road test.
Look for the VSS parameter - Vehicle Speed Sensor. Confirm that DDEC sees this so it knows bus is moving.It should show you same mph as your speedometer or be really close.If you don't have it, let us know. It might be turned off and can be turned back on with the ProLink.
You're also looking for the "Engine Brake Enable" or an auxilary output on A1. This parameter will be "ground" when Jakes are activated, it will show "open" when Jakes are not activated.Check this while you are driving your coach.
Have someone else look at ProLink, or let them drive your coach and you watch the ProLink. I would drive coach at least 50 mph, have dash Jake switch in hi or low position, release accelerator and expect Jakes to activate- as an example.

[RTS/Daytona]

Sammy

I believe that the "Engine Brake Enable - pin A1" is actually the LAST link in the chain of events needed to apply the Jake Brakes

Pin A1 will provide GROUND for the Jake Brake Solenoid(s) when the DDEC has decided that all the other conditions monitored by the DDEC will allow The Jake Break

to come on (no parking break / no fast idle / no clutch / and probably other that I do not know about) -

To test the A1 pin - plug in the prolink - set to input monitor "engine Brake enable" - press the throttle down and let it go quickly back to idle - the point should toggle between disabled and enabled.

Pete RTS/Daytona

[Sammy]

Hi Pete, thanks for your assistance with this.
I agree that DDEC will only allow Jake action after it "sees" all needed inputs.
I believe (just don't remember,lol) the VSS is one of the inputs DDEC needs for that final decision.
I have a copy of Jake diagram for Ace's bus and a copy of next series of same vehicle.
I studied them last night and they have the same wiring, just show left and right banks in opposite position.Wiring is the same. I can send 'em to you if you'd like to take a look.
I usually just put my ProLink on it as I said, but Ace is a little far from me to do that.
Let me know if you'd like those copies, can send them as 2 .pdf files.
Sammy