Help - Any common reasons or troubleshooting for DDEC III cruise control?

[belfert]

Are there any common reasons why DDEC III cruise control on a Series 60 would fail while in use and not work again?  Is there a troubleshooting flowchart anywhere?

I had the engine idling this morning to build up air.  I used the cruise control to increase the RPMs.  (DDEC III cruise can also control idle speed.)  After three or four minutes the engine suddenly went from high idle to normal idle with no intervention.  The cruise would no longer do anything to the idle speed.  I've stopped and started the engine multiple times to no avail.  The brake lights are not stuck on so I don't think the DDEC thinks the brakes are depressed.  (The brake light relay clicks when I hit the brake pedal.)

Thanks for any ideas on this.  I haven't been out on the road since this happened this morning, but I assume the cruise won't work if it can't control idle speed.  I would prefer not to drive 4,000 miles without cruise.

[Van]

Seems to me that if you you worry too much about idling in cruze, you ain't gonna get very far Take it out for a spin, and double check that it ain't functioning first, then there will be no doubt 

[rv_safetyman]

Brian, the cruise control has to have three conditions to operate in the fast idle function:  brakes off, parking brake set, and clutch not depressed.  You have already checked the brakes.  You don't have a clutch, but I am not sure how that is communicated to the ECM.  My engine came out of a truck and I had to wire the clutch switch out of the system.  So, I have to wonder how the ECM gets the signal that the parking brake is on.  In my case, I simply put a switch into the system that I could set to simulate the parking brake on.

If it is a parking brake issue, you may not have the fast idle, but it should work as a cruise control going down the road.

Jim

[belfert]

Okay, I need a dunce cap.  I took the bus out on the road and the cruise works, but the high idle stuff still doesn't work.  I don't really care about the high idle right now.  I'll look at the idle stuff when I get back.

I'm glad I didn't waste much time on this.  I was reluctant to take a test drive as sometimes it takes as long as 20 minutes to get back into my driveway after a drive.  I was lucky for the second day in a row that traffic was clear without waiting like usual.  (I have waited for upwards of 20 minutes to get a break in traffic both directions.)

Back to installing my trailer brake controller.

[belfert]

Jim, there must be something in my system that knows when the parking brake is on.  A don't shift light comes on when the parking brake is on.  I'll study the wiring diagrams after my trip.

[rv_safetyman]

Brian, your trip with the cruise control confirms that the parking "switch" is the problem. 

I took a look at the wiring information on my project pages and it looks like wire 524 is the parking brake wire.  Not sure what it connects to on your bus, but if you can find it, you could put a switch to send it to ground and your fast idle will work.

Jim