Does anyone know how the clutch master cylinder tells the clutch interlock switch that the clutch is pressed in to start the engine? I have ruled out the interlock sensor as the issue, and I am now thinking it's the clutch master cylinder, but I can't find anything online explaining how it functions. I have some guesses lol. Currently starting in 4low. 2012 JK Manual Transmission. Thanks!

 

Perhaps this photo I shot when I swapped out the master cylinder will help. I can make an educated guess how it works, but it's likely pretty much what you are thinking. You press the clutch and the master cylinder provides hydraulic pressure to the slave cylinder. At the same time it also activates the interlock sensor, which is a part of the master cylinder, sending that signal to the Jeep to allow it to start. I guess where I'm confused by your question is you suspect the master cylinder, but not the interlock switch, which is part of the master cylinder.

 

Thanks, Mark! I've pulled my interlock sensor and tested it in another Jeep and it works fine, which leads me to believe whatever triggers the interlock sensor inside the cylinder is faulty. I replaced my factory cylinder 6 months ago after a seal broke and all of the brake fluid emptied on my floor board. I used a car quest part because that's what was near me. I spoke to one of their technicians this morning, and he couldn't figure out what was inside the cylinder, because he didn't have access to the diagrams, but he is putting a new cylinder in the mail on Monday. I'll swap it out and keep you posted. Also, the interlock sensor pops off of the side of the clutch master cylinder.

 

Just to be sure why don't you unplug the connector and get a helper in the driver seat to turn the key to start when you have the two terminals shorted with a jumper of some sort. If it starts get new MC because I do not believe the switch is serviceable other than replacement of the entire unit.

 

This mechanism participates in the electronic controls & pressurizing the line and Slave Cylinder for starting a manual trans Jeep Wrangler; this is the 2012 part list price is $35.00 68029261AA SWITCH, Clutch Starter Interlock SWITCH, Clutch Starter Interlock Usage: JEEP - 4WD [J], JEEP - 2WD [T], JEEP - 4WD (RHD) [U]; SPORT UTILITY 4-DR TYPE #4 [74]; 6-Speed Manual NSG370 Transmission [DEH]. The picture posted by Mark is the switch & there is a sliding mechanism component inside. You might find this informative:

 

This is a good video, but it doesn't help me with my JK. At this point, I wish I had a TJ. Here's a photo of the interlock sensor on a JK.

 

Update: The jeep is back to normal after installing a new clutch master cylinder over the weekend. I ended up picking up a LUK cylinder, after installing the Car Quest replacement, and then finding out the slave cylinder line wouldn't seat into the new cylinder. The LUK park looked and felt just as good a Mopar. Moral of the story, don't buy Car Quest parts.

 

Thanks for the closure. Always helpful to future readers.

 

Were you able to remove the sensor (in the picture) with the clutch master cylinder installed?

 

A bit dated, but here's the procedure.

https://www.jk-forum.com/forums/jk-w...cedure-311575/