Cruise inop

[mystere900]

Took the coach out for exercise and the cruise control was totally dead. No lite on the dash, no work. Probably the first thing I should look for is the fuse. Anybody know where that little devil might be located?

Thanks,

Roger

[wa8yxm]

Depending on the make and model the CC can be in several locations. DANA Cruse Controls (Last I knew they sold to Rockwell, but last I knew was like 1980) are the ones I knwo best, they made two models

One the vacuum canister/solenoid (There is a cable from this to the throttle) contained all the electronics, I believe this is how it's done on my 1992 Chevy towed. The other had a box, under the dash with most of the electronics.

However... If I were buliding one today.. I would use the Engine Control Computer and make it a sub routine.

ONE thing that will cause both CC and ABS to fail is the brake light switch by the way.

[chasfm11]

Roger, the cruise control on my Freightliner chassis is controlled through a combination of electronic means. The signals from the cruise control switches on the steering column are routed through the main wiring harness to a Vehicle Interface Model (VIM). My VIM is located in a compartment on the right rear of the RV. Combined with road speed data information feed from the Transmission Control Module (TCM), the Engine Control Module (ECM) on my Cummins actually controls the engine to maintain the required speed. I'm not aware of any fuse in the circuits, but that doesn't mean that there isn't one.

I had a very difficult problem to troubleshoot on my speedometer. In the couple of years of working on that highly intermittent problem (now fixed), I learned a lot about some of the wiring. Assuming your chassis is somewhat similar, here is how I would suggest going about trouble shooting the problem.
1. Get a chassis wiring diagram. Without that, you will have no way to determine which wires indicate "cruise control on" to the controlling circuits. Years of computer trouble shooting taught me to always suspect the mechanical parts first so I'd make sure that the control circuits could "see" the "on" switch and the "set" switch for the cruise control. Missing either one of those will give you an inop condition.
2. On mine, the cruise control failed when the speedometer failed because the roadspeed data was not making it to the ECM. You didn't mention other faults like the speedometer needle behaving strangely or shift inhibit problems with the transmission which might indicate problems with the roadspeed data circuits. Your CAT might be different than my Cummins in this regard. I was definitely getting an error code set "road speed data invalid" on the chassis messaging. Do you ever get a check engine light?

I believe that if you have good roadspeed data and the cruise control switch settings are being sent to the controls, you may have an ECM problem. Perhaps a reflash may be necessary. I would definitely make this the last resort, however.

Let me add a commerical for VMSpc. It is a computer monitoring program which can run on a laptop. I bought it several years ago just for situations like yours. For example, VMSpc can show me cruise control speed set. This means that I could drive at 45, push the "set" button and a second or so later, see a display on the computer screen show that my target cruise control speed was set to 45. It I couldn't change the cruise speed set, I'd have a stronger suspicion about the set switch communicating with the controls. It might be a way to "divide and conquer" whether you were setting the cruise control or whether after it was set, the control mechanism wasn't doing anything to maintain speed. Of course, a good chassis shop should be able to plug into the diagnostic plug with their computer and see the same things that VMSpc shows me - and potentially even more.

I hope this helps.

Charlie

[EngineerMike]

I vote for brake light switch. If your brake lights are perpetually on then that is almost certainly it, or it is related to this circuit.
I would bet your cc is simply a program in the ECU based on inputs cited above.
Most cc programming uses brake switch as a trip to kill the cc setting. If it is frozen "on," you cannot engage cc. We have seen several (not any high percentage tho) brake switch failures that cause interference w/cc, tho the usual is cc won't shut off when braking (which is worse). Check the link for discussion of the diagnostics. If the switch is performing properly, your problem is elsewhere, maybe in vehicle speed sensing.

[JayLodge]

Charlie (ChasFM11)
On my 2006 Tour, my CC seems to be more of an engine RPM/throttle lock! That is, the vehicle still speeds up going down hill / slows going up. Given the nature of the Cat engine, etc, didn't surprise me, but this thread seems to indicate the rest of you truely have CC. ? ?

[mystere900]

Somewhere a long ago I was told that if a gadget suddenly stops working, go back to the last thing you did and look around. Well last week I had done a chassis lube and was in the coach at the bottom of the steering column looking to lube the upper u-joint. Couldn't get the rubber boot loose so I gave up on that part of the lube process. (Have to start another thread for that problem.) While down there I must have moved some wires around and pulled a wire (the red one) out of a 4 lead plug coming from the steering column. Pushed the wire back into the plug and "viola" everything works as advertised. KISS strikes again.

Thanks to everyone for their help, I'll keep these suggestions for future reference if I have a real CC problem.

[Kerry1956]

Mine is on the same fuse as my brake lights for some reason.

[chasfm11]

Quote:

Originally Posted by JayLodge Charlie (ChasFM11) On my 2006 Tour, my CC seems to be more of an engine RPM/throttle lock! That is, the vehicle still speeds up going down hill / slows going up. Given the nature of the Cat engine, etc, didn't surprise me, but this thread seems to indicate the rest of you truely have CC. ? ?

Jay, I'm not sure what you are saying. Cruise control generally is a way of CHANGING the engine speed to try to keep the speedometer (roadspeed) constant. Going downhill, the engine RPMs should drop but the speedometer speed may increase because the overdrive is allowing the vehicle to run faster. Short of having the CC apply the brakes, there is nothing that it can do to alter downhill roadspeed. On uphills, CC cannot anticipate the length or steepness of the hills. That is why driving with CC in hilly terrain can have a very negative effect on mpg. In general, my CC does not apply enough throttle to overcome speed loss soon enough, resulting in unnecessary downshifts. My engine monitor shows a drop in mpg when that happens.

My comments were based on the information that I gained about how the CC on my chassis worked, not necessarily how successful it was when it did work.