I was hauling a load of furniture from Amarillo to Nashville, Tn this last week when my cruise control stopped working. The dash light will come on OK, but the cruise won't hold a speed. Sometimes it will hold the speed for a few seconds, the abruptly turn loose. Sometimes it'll hold a few minutes. Any ideas? I hate to take it to the dealer. Long out of warranty. Any help would be appreciated. I put on too many highway miles to do without.

 

OK... the cruise is easy to troubleshoot if you've got a scan tool and not so bad even if you don't.

Cruise control is done by the ECM on 3rd gens.

There is one wire that goes from the ECM to the cruise control buttons in the steering wheel. There is another wire that goes from the steering wheel buttons to the the ECM that has different voltages for each of the cruise functions, like set, resume, cancel, etc. Both of these wires go through the clock spring, as does the horn and airbag. (Does your horn work ? Does your airbag light come on ?)

There are two other wires that control the cruise control as inputs to the ECM. They are the brake and the emergency brake signals. They serve to shut off the cruise function if you press on either one of them. Do you have any problems with your brake lights or the emergency brake light not going out ?

If the cruise is not holding speed, I would suspect a short in the set/accel button on the steering wheel.

 

I had a problem with mine several months back and it turned out to be two different problems the first was an bad brake switch that was shorting out between two of the three seperate switch elements but the second problem and the finial bad one was the electric vacuum pump that is mount on the passenger side back by the firewall was not keeping up with creating enough vacuum and the cruise system would drop out and not allow it to be reengauged till after you turned the engine off and let it set a bit and then restart it. At the time the service Tech had to get the STAR support center envolved because no error codes are set by this type problem and it turned out the electric vacuum assembly was on hold and only with STAR center OK was an replacement unit sent.

 

My 05/manual transmission has no vacuum servo. Everything is done electronically.

Does your 04 use a vacuum servo ?

 

What I've seen fail most often is the brake sw. , I do not know what color the wire at the sw. to test but sometimes the easyest test is to use your foot and lift the peddle and keep pressure on it and see if the cruse works , if it does then let go of the pressure holding the peddle up and maybe the next bump you hit will turn it off , if that works hot glue a small washer on the foot of the sw. or bend the mount that its in just a little 1/8-3/16 ,

 

The 03-04 trucks with automatics still used a vacuum powered servo controller to do cruise controll. This servo unit is what was used in the 04 automatics to give the user the manual higher idle feature. Code was added to the ECM in the 04 model year (for manual controlled high idle) as the automatic transmission started being run by the ECM and not a seperate PCM controller.