Hey all, a few months ago my cruise control stopped working. Yesterday I started diagnosing. I checked the common brake pressure switch on the end of the master cylinder: it has continuity when no pressure, and open circuit when pressure applied (I believe this is the right behavior), so it's fine. I checked my brake lights and they light up with the brakes. It's a 6 speed, haven't checked the clutch switch but the truck starts no problem (which requires depressing the clutch), so not sure how that could be the problem. I don't have any ABS issues. I don't have any SRS issues. No codes come up related to cruise control/brakes/etc.

I then realized that the little green cruise control indicator light on the dash never lights up, even during the key on self-test. I tried doing the cruise control diagnostic thing where you hold the OFF button and cycle key-on key-off a couple times, but to no avail.

Does anyone have a good grasp of best next step? I've taken the dash off before so not opposed to doing that if the best next step is to test the dash indicator light itself... but I feel like that wouldn't actually stop the cruise function from working?

I have an ELM OBDII adapter and Forscan... no idea if Forscan has the ability to read the inputs from the switches in the steering wheel. I also saw a fella manually check the switches by probing some connector in the engine compartment, but I can't find that connector in the mess of wires.

Thanks for your help,
John

 

Did you check the fuse for the cruise control?

 

Forgot to mention that, yes I did. I specifically checked the 2A fuse for the brake/speed control. Also went through and checked nearly every fuse.

 

Switches look worn?

Maybe a bad clockspring?

 

Yeah... I'm trying to avoid shooting in the dark here and replacing every conceivable component. Was wondering if anyone knew exactly why the cruise control light wouldn't illuminate when you go key-on and the rest of the dash turns on (other than the bulb being burnt out).

 

If I'm not mistaken the clutch switch has 2 switches in it, 1 that allows it to start & 1 that is for the cruise. If it's not this I'd say it's the button or clockspring.

 

Correct, on the wheel there is: On, Off, Res, Set/Accel, Coast. Would any of those switches malfunctioning cause the cruise control dash light to not illuminate during the key-on selftest?

 

Checked instrument cluster bulb, it's good.

I started taking off the cruise control switch covers on the wheel. Looks clean enough inside. I did notice an interesting behavior that isn't explainable looking at the electrical diagram: If I press the On and Off microswitch at the same time, the horn beeps. Also if I press the On and Coast microswitches at the same time, the horn beeps. Might end up being a clockspring after all.

 

Pretty sure I have a faulty clutch position switch. Been doing some digging and found out the starter circuit uses different signal wires than the speed control circuit. Pin 3 of the clutch position switch goes to the PCM and should read 12V normally, 0V when pedal depressed, but it's reading 0V always. Gonna try swapping that tonight and see how it turns out. Pins 1 and 2 are for the starter circuit and control the starter relay.

The diagrams on Alldatadiy have been invaluable.

 

All fixed. Replaced the clutch switch and all is good now.

Here's a couple pictures of the old clutch switch. Looks like the springs lose their sproing. Perhaps if someone finds this in the future they can try replacing the two springs for a couple bucks instead of the whole switch for $40.

this is how far back the white piece should go

worn out springs don't push white contactor far enough back.


Also worth noting: on my 2004 6.0, the cruise control dash light does *not* illuminate during the key-on selftest. When I took apart the instrument cluster to check the bulb, I found out it's a surface mount incandescent holder, while the other dash lights are soldered on LEDs. Maybe just overlooked in the software to illuminate the cruise control bulb during the key-on light up show.