Cruise Control

Don't know if yours is setup this way or not, but a common problem on 18 wheelers is the parking brake switch. ECM needs to see park brake released for cruise to work and park brake set for high idle to work. Try setting high idle and release parking brake. If high idle kicks off, then this is not the problem. If high idle does not kick off this MAY be the problem.

Mr marks idea about jake switch is great too. Mine has exhaust brake but cruise will not work with exhaust brake switch on. I have changed every setting in ECM that looked like it might let cruise work with that switch on but no luck.

If you have a jake brake switch, the cruise will not engage if the switch is in the ON position. That's how ours works.

Good luck,
MM.

If a brake light bulb is burned out the cruise control may not work.

Also remember that any brake light grounding will cause it to come off. Can you slip a small digital camera and a light under the hood to the cruise control to see if it is engaging (or at least a meter to test for 12V) at the cruise control box?

I tried it many times on the 200 mile drive home. If it was the brake pedal switch, surely the cruise would have worked on one of those attempts over a 200 mile drive. However, I will check the brake light switch tomorrow and then post again the results.

Thanks for the input guys.

larrylu62 wrote:
I let it idle and ran the engine up to about 1000 rpm. Then I switched on the cruise and it held the 1000 rpm as if it was working.

On my coach, that is how the High Idle is activated.

Depends on where the speed pickup is connected. If it is sensing actual drive line speed, it will not work unless you are actually moving. Also, they usually will not work under 30 mph or so.

Some times the brake light switch at the brake pedal will cause a problem. If the switch isn't properly adjusted to contact the brake pedal shaft it can cancel the cruise control when you hit a bump in the road.

Sounds like it's working. Have you tried it on the road yet?