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Discussion Starter #1
I hope I'm posting in the right forum, if not please direct me.

I purchased a 2008 3.7l Jeep Commander from a friend and so far everything had been running ok. During the past three months, however, I noticed there were times when I got into the vehicle is would not start. All I would get was a clicking sound. Now before you think starter or battery, it wasn't coming from either of those. The clicking sound was actually coming from somewhere on the fuse box in the footwell of the driver seat. After a thorough investigation, I could also feel a click in the fuse box in the engine bay. (fuse box on driver side closest to the windshield. If someone can give me names for each of the two, that be great). While this is happening, I'll have to add that a red security light so it seems blinks in the dash. There is the power to everything, but it just doesn't start. The famous yellow wire fix has been done along with a brand new starter. IOD pull out has also at times been performed letting the vehicle start or sometimes not. Same thing with battery disconnect. The battery is good along with a new battery on the side. The same thing happens. Lastly, the ignition switch recall was just done two weeks ago, didn't fix the problem.

Last week I ran the OBD and got a code of U0100. Lost communication with ECM/PCM A. It shows two possible causes, can "C" bus circuit is open or shorted to ground and or TCM has failed. The top two reported fixes were to replace the powertrain control module and or replace tipm. WHat is what and where are they located?

After even more research, I found out the red light is blinking may be SKREEM related. Although it does this at times I did run the obd code again and got a U0100 code again. Along with this OBD reads Can bus C, what exactly is that? Where is it located?

Thank you in advance for any suggestions and or replies
 

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The fuses in the footwell of the driver are on the Junction Block -- see this for its functions. Junction Block explained
 

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Discussion Starter #4
The fuses in the footwell of the driver are on the Junction Block -- see this for its functions. Junction Block explained
Nice write up. So let me ask, now that I know that's a Junction block, what are the other two fuse boxes in the engine compartment called? I'm talking about the ones that also contain fuses and relays
 

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OK another post I made that might help
 

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Discussion Starter #6
Well after doing thorough research, I'm beginning to think it has something to do with the WCM (wireless control Module). The question is, can I get one of those already preprogrammed with my vin so I could bypass the dealer and its upped costs? I'm surprised some recalls fixed the WCM but on the 08 commanders, it was just passed up. Weird and strange if you ask me
 

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Discussion Starter #9
I wanted to add. When the vehicle is at the on position right before the engine is turned on there's an electronic throttle control light that illuminates. I'm not sure if it's supposed to be on normally. However, if this icon is on, the vehicle will start without any problems. If it isn't there when it's on the on position I know the vehicle will not start and the red security light will start blinking. Just adding in some more info in the help of diagnosis. Thanks, guys, and gals
 

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Discussion Starter #10
Hello there,

So here's an update of what is going on. Any suggestions, please chime in. I figured out that if I pull relay 8 (R8) in the Power distribution center while the jeep is running and keep it out (vehicle shuts off) then go to the ignition and turn the key off then on (of course jeep won't start because the relay is pulled) I get the clicking sounds I talked about previously. I also get the security light that blinks red. I then put the relay back in and continue the same thing and the clicks and red light blink as it would have if I had droved somewheres and parked. After going off and on, eventually red light is blinking Z with lines appear as I mentioned before and the vehicle starts.

From this, I believe I pinpointed the problem, but from here, what next? Could anyone try doing what I explained and see if that too happens to them? I'm really curious.

I also checked all grounded areas and everything is good and on tight. I thought maybe I could ground the starter directly to the negative post for the ultimate ground but now that I've discovered this issue, I dont think it has nothing to do with the starter. Curious if anyone has any suggestions. Thank you!!
 

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I went through that exact issue early last year - 4 months of not knowing if the truck was gonna start when I needed it to. Sometime it'd start if sat inside, shut the doors, armed the alarm, wait for the flashing red light, then unlock with key fob and it'd start right up. Hours of reading online/forums and testing various things got me to replace the WCM. Fairly cheap for the part. Tear your dash apart before taking it in to a decent shop (saves labor) so they can install the module and code your keys. That worked like a champ for 2 weeks...then same issue. On to the next potential issue - the starter. The Commanders are infamous for having corroded connectors @ the starter. Bought one cheap online, got the truck to start, headed to my local shop. Sure enough, corrosion out the yin-yang. New connectors on the cables, new starter, and new battery just because. WOOHOO! Goin' strong...for another 3 months. Same sh*t, different month. Turn the key - nothing. Not even a hope-inspiring "click." Until I "accidentally" put a LOT of sideways pressure on the key (kinda like I'd wish the key would just break off in the ignition) - while holding it @ "Start" - and it fired right up. Repeated the process 5-6 times with success. Apparently I beat the sh*t out the ignition switch trying to start the truck over the last 6 months. $20 dollar part and 1.5hrs of pulling the dash off and wriggling the the ignition out.

Save yourself some time and start with checking the starter connections. Had I done this I could've saved myself some $$$ and frustration. You can do any of this on your own with exception to reprogramming the WCM if needed - I chose to have a shop do my starter because it's a PITA on the Hemis.

Anyway, a few things for you to think about. I've lived your previous posts and the symptoms to a tee.
 

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I went through that exact issue early last year - 4 months of not knowing if the truck was gonna start when I needed it to. Sometime it'd start if sat inside, shut the doors, armed the alarm, wait for the flashing red light, then unlock with key fob and it'd start right up. Hours of reading online/forums and testing various things got me to replace the WCM. Fairly cheap for the part. Tear your dash apart before taking it in to a decent shop (saves labor) so they can install the module and code your keys. That worked like a champ for 2 weeks...then same issue. On to the next potential issue - the starter. The Commanders are infamous for having corroded connectors @ the starter. Bought one cheap online, got the truck to start, headed to my local shop. Sure enough, corrosion out the yin-yang. New connectors on the cables, new starter, and new battery just because. WOOHOO! Goin' strong...for another 3 months. Same sh*t, different month. Turn the key - nothing. Not even a hope-inspiring "click." Until I "accidentally" put a LOT of sideways pressure on the key (kinda like I'd wish the key would just break off in the ignition) - while holding it @ "Start" - and it fired right up. Repeated the process 5-6 times with success. Apparently I beat the sh*t out the ignition switch trying to start the truck over the last 6 months. $20 dollar part and 1.5hrs of pulling the dash off and wriggling the the ignition out.

Save yourself some time and start with checking the starter connections. Had I done this I could've saved myself some $$$ and frustration. You can do any of this on your own with exception to reprogramming the WCM if needed - I chose to have a shop do my starter because it's a PITA on the Hemis.

Anyway, a few things for you to think about. I've lived your previous posts and the symptoms to a tee.
Also should add that I went through many times the truck not starting - good thing I had my pliers on the seat next to me ALWAYS - so I could jump out, pull that exact jumper out, wait 10 minutes and/or turn the key 10 times to discharge the system, pop the jumper back in and start right up. That'll only last so long though...
 

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FYI - this is the "ignition switch" part I'm referencing. It mounts to the end of the ignition and is actuated by a plastic "pin" that rotates as you turn the key.

40694
 

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Discussion Starter #14
Feels good to know someone went through what I'm going through lol and thank you for the response. I wanted to add that the ignition switch is brand new. I just got that recall done about two weeks ago. Just like you, however, it did not fix the problem. The starter is completely brand new and all wires were checked today up to the T. Nothing is wrong pertaining to the starter or ignition. Yellow wire upgrade has also been done and is secured but just like you, back to the click and red dot blinking lol! Relay is also new. Did you end up completely fixing the problem or just lived with it?

I had my friend come over and while he turned the ignition I went on under the vehicle so I could find out where the buzzing noise was coming from. It was definitely not the starter but somewhat behind it. I placed my hand on the transmission and I felt it there from inside. Now, remember, when this intermittent problem happens the buzzing occurs. If the Jeep starts normally, no buzzing. I re-ran the scan just for ****s and giggles and what I got was, lost communication with ECM/PCM one of the possible causes is TCM has failed. Is that transmission control module?? If so, where is it located? The other is can the C bus circuit is open or shorted to ground. I don't even know what can A,B,C,D, are.
 

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I didn't see mention of the trans "buzzing" before - that's one thing sets your experience apart from mine. You've got some funky electronic issue going on. From what I've scanned in the forum the TCM is either a work or no work scenario. TCMs are $700 new (plus labor) or ~$100 refurbed (plus labor). My $.02 would be to clear all the codes (if you haven't yet today...) and see what happens when u try to start it. Check u battery 1st and make sure you've got at least 12.35 volts coming out. Does your dash light up, headlights come on, radio scare the sh*t out of 'ya, etc... - when key is in the "on" position before turning to "start?" If so, and you turn to "start" but get nothing, specifically no "click" for the starter, I'd take a look @ the WCM (Wireless Control Module). It controls/manages a ton of crap from unlocking the doors to disabling the circuit to the starter motor. It also manages crap you don't think about - the TPMS system. There's 3 remote sensors that transmit all data to the WCM. If you experience the "no click" run through the steps here - How to Reset the Immobilizer on a Jeep Grand Cherokee and Reset Anti-Theft - it's for the JK but actually worked for me many times. Just a little somethin' more to keep hope alive. Lemme know how it goes...
 

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BTW - to answer a question - I'm Golden now. No issues in months. I even go outside at random (middle of the night???) times to start it up just for my sanity - I put a lot into fixing that issue. Root cause could be the starter, WCM, or switch. I don't know for sure since they all interacted with/affected each other.
 

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Discussion Starter #17
I didn't see mention of the trans "buzzing" before - that's one thing sets your experience apart from mine. You've got some funky electronic issue going on. From what I've scanned in the forum the TCM is either a work or no work scenario. TCMs are $700 new (plus labor) or ~$100 refurbed (plus labor). My $.02 would be to clear all the codes (if you haven't yet today...) and see what happens when u try to start it. Check u battery 1st and make sure you've got at least 12.35 volts coming out. Does your dash light up, headlights come on, radio scare the sh*t out of 'ya, etc... - when key is in the "on" position before turning to "start?" If so, and you turn to "start" but get nothing, specifically no "click" for the starter, I'd take a look @ the WCM (Wireless Control Module). It controls/manages a ton of crap from unlocking the doors to disabling the circuit to the starter motor. It also manages crap you don't think about - the TPMS system. There's 3 remote sensors that transmit all data to the WCM. If you experience the "no click" run through the steps here - How to Reset the Immobilizer on a Jeep Grand Cherokee and Reset Anti-Theft - it's for the JK but actually worked for me many times. Just a little somethin' more to keep hope alive. Lemme know how it goes...
I've asked many times lol, maybe I can now finally get an answer. What the heck is a TPM??? Where the hell is it located?? Are the ECM, PCM, and TIPM all the same shi**? Please answer lol

Codes have been cleared about 9 times now lol! Crazy thing though, is after interment starting issue, once vehicle starts, the cluster is free of lights lol! The battery is ultimate. Just for fun, I even have two more, those are fully charged. Dash, lights radio, all work fine. Nothing is dimming, nothing is struggling. I wondered if the problem was the WCM. I'll continue diagnosing once it's dry out.
 

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TPM(S) = Tire Pressure Monitoring System - pretty sure u new that but being inundated with all the 3 letter acronyms does get confusing. Those are the wireless sensors in your wheels for air pressure - that data also gets sent to the WCM. The important thing to note when attempting to start, especially knowing that you've got an abundance of power, is whether or not you hear any clicking.
 

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Discussion Starter #19
TPM(S) = Tire Pressure Monitoring System - pretty sure u new that but being inundated with all the 3 letter acronyms does get confusing. Those are the wireless sensors in your wheels for air pressure - that data also gets sent to the WCM. The important thing to note when attempting to start, especially knowing that you've got an abundance of power, is whether or not you hear any clicking.
Sorry, but I meant to type in TCM. Of course, TPMS are the sensors lol. I wasn't sure with Jeep if its Throttle control module or transmission control module. I found out where it's located as well. The intermit start issue continues on ughhhhhh
 

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Found the TCM in the service manual, Transmission Control Module.
40703
 

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