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Discussion Starter #1
Hey guys, almost had a scary situation the other day. Had cruise control set at 80 on my 2000 7.3 and had to get off on an exit quick. I hit the off button on the steering wheel; nothing. Hit the brakes; nothing.

Stepped on the brake pretty hard to see what would happen and the truck started shaking bad, the engine was really trying to fight the brakes and maintain speed. I had to put it into neutral and coast to a stop on the exit. Put it back in drive and it was fine

What should I look at? I know there’s a brake pedal sensor on the master cylinder and near the pedal itself that has something to do with disengaging cruise control. Although I think if these were bad it would still shut off with the button on the wheel. Anything I should look for?

I just got new custom tunes from Jelibuilt Performance, I cant remember if I had it in cruise before this happened with the new tunes, I think I did and it was fine. So probably not an issue with tuning, but possible I guess


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Looks like you need to do some lower speed testing -- then maybe revert the tune and re-test

Yes, the brake pedal switch should have cut the speed off -- or the Cancel button
kick the tranny in neutral, should auto cut off at 30 mph
 

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Some simple questions first. Does the horn work? Brake lights work? ABS light illuminated?
As @Hydro stated, revert to stock and retest at a lower speed.
Then on to the basics.
Check the connector to the sw @ master cylinder as well as near the pedal. Ohm out the switches with pedal engaged and disengaged.
 

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I have personally experienced cruse control issues if I have cruise on and then change tunes etc. now I turn cruise off, let the truck coast for a millisecond then change tunes and resume. Im betting its whats happening to you. You running a tune, with cruise on then change and the ecm is still running cruise based off the prior ecm setting etc. I feel it should be a warning on the labels/instructions but maybe it doesn't happen enough or we both have strange trucks lol.
 

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Discussion Starter #6
I didn’t change a tune though, I was in my daily tune the whole time on the highway. I’ll have to check sensors when I get home, I heard there is a recall on the one on the master cylinder


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I changed the sensor on my master cylinder a while back because the cruise would either not engage or it would disengage on its own. I found out that the was a recall on it years ago because the factory sensor would leak and had the potential to start a fire under the hood. The replacement part was less than $20. Simple fix.
 

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Discussion Starter #8
I think I’ll try that, mine appears to be original.

I still think the button on the wheel would have shut it off though, if not the brake pedal


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I still think the button on the wheel would have shut it off though,
if not the brake pedal
There are only three inputs to the PCM for the cruise in a Diesel. The steering wheel buttons, the hydraulic switch on the M/C, and speed (gry/blk wire) from the ABS module. The "cruise control" is contained entirely within the PCM.

One would think the steering wheel should shut it off, but the "off" button is not a "switch". The PCM interprets the resistance for the buttons as certain commands, including the off command. The horn is zero ohms, the cruise buttons are higher, each of them is different. If cruise sets, and responds to up/down speed commands, the OFF should function too, as the PCM has to interpret the different resistance values for the different buttons. Including "off".

The only cruise brake input controlled by the brake pedal is the hydraulic switch on the master cyl under the hood. It is a normally closed switch. If the switch contacts are open, or there is no power to the switch in RUN, the cruise will not set. The switches inside the truck on the pedal for the lights, shifter lock, etc have nothing to do with cruise.

I think you have a tune problem. It ignored BOTH inputs to disengage.

Turning the key off should disengage the cruise as well as solve the "runaway" problem. Something to remember if it does it again.
 

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Discussion Starter #10
Great info, thank you. I will do some testing next time I have the truck out to see if it acts up consistently and if it does I will contact Brian at Jelibuilt Performance to see if he can fix any tuning issues


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