I changed out my clutch this weekend and afterwards, I had codes C121C, PO300, and PO335. This thread and a couple of others lead me to replace the crankshaft position sensor. That didn't work but next, I replaced the harness and it completely fixed mine. No more check engine light and no more codes! Thanks for posting this thread. It really helped me narrow down what I needed to troubleshoot. By the way, I bought the $20 sensor from Advance Auto Parts and it works fine. Mine is an '08 JKUR with manual transmission.

Here is the sensor.
http://shop.advanceautoparts.com/p/c...ontent=general

And this is the harness.
http://shop.advanceautoparts.com/p/c...ontent=general

 

Nice! Super glad it worked for you! More thx & kudos to C-T-R for the great tip!

I've unf continued to have issues with this sensor. Have had luck for short bursts by disconnecting the battery and discharging any resistance. That clears the errors & she runs beautifully for 40/60 miles, then throws the crank sensor code & begins running rough again. My clutch is in dire need of replacement, and feel it has something to do with it. Can't afford a shop clutch repair at the moment (have gotten $900 to $1200 estimates fr a few local shops), so she's been sitting (sadly) in the garage for some time.

Have contemplated doing the clutch myself, watching vids and reading blogs here on the subject. But I am far from a mechanic, and the task is daunting. Did you do the clutch work yourself, or have a shop do it?

 

07 JK Automatic,
On my way to work this morning the Check engine light came on, the Jeep bucked a bit, then the CEL started flashing and beeping at me.
I was cruising down the freeway when it happened but I managed to dig my bluetooth obd2 scanner out of my center console and check the codes while still chugging along.
P0335 CPS and P0300 Random Missfire. After work I swapped out the CPS ( what a pain in the ass on a stock height JK, apparently I could stand to loose a few pounds). Anyhow, as soon as I cleared the codes I fired it up and just reving the gass in the parking spot it poped P0300 flashed and ran like crap. With light fading I decided to limp her home, I thought it had fixed itself but after a few miles the miss fire came back.
The area around my cps was greasy and muddy, i'm a bit worried I might have got a lil bit of crud on the end of my new cps since I was installing it blind. I'll pull it out tomorrow and check its cleanliness, Should the wireing harness be my next course of action? I'm well versed on XJ's but know very little on the JK.

 

Did you find out anything. I'm in a similar boat with my 2012 JKUR. The P0303 code and P0339 codes both came up for mine yesterday. Was going to get the part from Napa, but not sure if there is something else you discovered in your struggles.

 

2009 jeep unlimited. I have also had these same codes. Just picked up this jeep. Had evap issues. Backfire issues and cut out while drivin. I replaced gas cap. Replaced canister. Did the smoke check. Still getting evap. Until just on a whim put a wrench on the intake manifold bolts. Wow very loose tightened them up to specs for torque. Evap issue gone. When I got the jeep the prior owner had replaced the plugs and wires. Still was getting a misfire code. Pulled plugs thinking fouled probably running too rich. But found a new plug with cracked insulator. Replacing it. But I could not figure out intermitant cutout. Tried cam shaft sensor but no good. So I will try the crank sensor. I will remember the harness, thanks for the info guys.

 

My jeep starts and runs perfect. BUT HOW CAN THIS B . The crankshaft position sensor is off and disconnected. I dont understand. Anyone???

 

This thread is relevant to my interests. My '08 JK X pretty much simultaneously started misfiring at highway speeds and blew the upper radiator hose off. Replacing the thermostat and radiator cap and need to pull codes to see what else is wrong.

 

bboy - you may have a head gasket going if the rad pressurized fast enough to push or burst hoses off. Regarding old hoses, people don't realize but the new fluids eat the shit out of hoses and they have to be replaced every 3-5 years. But that does not solve your issue. Codes might help on the forum.

The thing is a lot of our Jeep friends in the US do a lot of freeway driving daily and they sure go fast there (Texas common to do 85-90) which is hard on these underpowered Jeeps for keeping up with the pack. Up here in Canada a lot of our driving is 2 lane roads so 60-65mph is it and easier on the engines especially the 3.8's (but mine is bigger than 3.8 now but still go slow).

 

Had the same deal with my 2011 Jeep wrangler. Changed clutch at a shop and got engine misfire codes. Changed plugs, coil and wires and still....I'll check on the harness tomorrow...thanks for posting this...it's driving me nuts!