Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
The "thing" is a capacitor for the ignition system to reduce electronic noise. It's labeled as such in the picture you posted 
Found my "no bus" ,still crank and no start
- Thread starter jeepdreamer
- Start date
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
There is a known problem in certain year XJ's and TJ's that the clockspring in the steering column can short the 5v reference in the PCM.
The diagnosis is unplugging the clockspring and then cranking it over.
The diagnosis is unplugging the clockspring and then cranking it over.
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
The main PCM grounds are where the negative battery cable bolts to the block. The 2 black/tan wires.
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
So it is... Oops!The "thing" is a capacitor for the ignition system to reduce electronic noise. It's labeled as such in the picture you posted
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
So where does one find this clockspring connector to unplug of which you speak??
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
Does front or rear of those two matter? Can't see how it would but I feel like in getting dumber. Haha
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
First and foremost, you need to find out why there is no communication to the scan tool. Diagnosing this problem may well also fix the no start.
The most basic and #1 step for diagnosing communication is checking that the PCM has a good power feed and good ground.
Check for power and ground at the PCM like this:
disconnect all 3 PCM connectors. the black one is connector 1 (C1) You can see the terminal numbers if you look closely at the connector face.
with a test light connected to ground and the key ON, carefully probe terminals 2 and 22. both should light brightly.. if not, check fuse 11 in the junction block, and fuse 22 in the PDC, respectively.
turn the key off
connect the test light to batt+ and probe terminals 31 and 32. the test light should light brightly. if not, check for good continuity in the ground circuit.
The most basic and #1 step for diagnosing communication is checking that the PCM has a good power feed and good ground.
Check for power and ground at the PCM like this:
disconnect all 3 PCM connectors. the black one is connector 1 (C1) You can see the terminal numbers if you look closely at the connector face.
with a test light connected to ground and the key ON, carefully probe terminals 2 and 22. both should light brightly.. if not, check fuse 11 in the junction block, and fuse 22 in the PDC, respectively.
turn the key off
connect the test light to batt+ and probe terminals 31 and 32. the test light should light brightly. if not, check for good continuity in the ground circuit.
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
I don't understand the question.
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
Under the steering column cover.
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
Thanks a bunch Digger! The shop (Ft Myer auto skills hobby shop) is closed now so it will be Wednesday evening before I can go over and check it out. Great info and I appreciate it more than Thank you can cover. Ill let you know what that turns up.
any single one of the 5v fed engine management sensors can cause a no bus situation.
what's happening (most likely) is that you're seeing no bus on the odometer because the PCM is shutting itself off. That's why you've got no OBD port.
Start unplugging engine management stuff one at a time. Unplugg something, turn the key to run, see if the fuel gauge works.
I've had oil sender and TPS failure and shut the jeep off with the same error. Anything that's fed 5V from the PCM may cause this.
That's your #1 suspect is something on that 5V rail after you verify power and ground to the PCM.
what's happening (most likely) is that you're seeing no bus on the odometer because the PCM is shutting itself off. That's why you've got no OBD port.
Start unplugging engine management stuff one at a time. Unplugg something, turn the key to run, see if the fuel gauge works.
I've had oil sender and TPS failure and shut the jeep off with the same error. Anything that's fed 5V from the PCM may cause this.
That's your #1 suspect is something on that 5V rail after you verify power and ground to the PCM.
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
Digger87xj... followed your test and 2 and 22 lite up fine. 31 and 32 do as well.
Any other ideas?
Any other ideas?
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
Ok, this is getting ridiculous. A buddy of mine and I went through the wiring again last night and it still won't fire. Here's what we tested.
-crank sensor. Good w 5v
-cam sensor. Good w 5v.
-tps. Good w 5v.
-map sensor. Good w 5v.
-pulled the connections off the computer and did the test for them. All good.
-realized my key fob wasn't working because I had gutted the interior. Put the dome light back in (the receiver for the fob is in it) , put new batteries in the fob, it works fine again.
Checked all the fuses (again!) and all good.
In not getting "no bus" anymore as it was traced to the airbag module not being installed on the transmission tunnel.
The fancy shop snap on scan tool will connect but not read any data.
My buddy used his weird phone app scan tool thingy since we figured maybe it would do something different. Well, it does... Sorta. It is able to "see" some stuff. Reads fuel, voltage, temp, and some other things. But what it does not see are rpms. Interesting. We crank the jeep and everything except the rpms register on his phone. So that brings me back to the crank sensor... Maybe? I am stumped. He's stumped too.
I guess ill go by the store and see if I can buy another crank sensor and see if that helps. Can't see how it would as the one in there tests fine but what else can I try?
-crank sensor. Good w 5v
-cam sensor. Good w 5v.
-tps. Good w 5v.
-map sensor. Good w 5v.
-pulled the connections off the computer and did the test for them. All good.
-realized my key fob wasn't working because I had gutted the interior. Put the dome light back in (the receiver for the fob is in it) , put new batteries in the fob, it works fine again.
Checked all the fuses (again!) and all good.
In not getting "no bus" anymore as it was traced to the airbag module not being installed on the transmission tunnel.
The fancy shop snap on scan tool will connect but not read any data.
My buddy used his weird phone app scan tool thingy since we figured maybe it would do something different. Well, it does... Sorta. It is able to "see" some stuff. Reads fuel, voltage, temp, and some other things. But what it does not see are rpms. Interesting. We crank the jeep and everything except the rpms register on his phone. So that brings me back to the crank sensor... Maybe? I am stumped. He's stumped too.
I guess ill go by the store and see if I can buy another crank sensor and see if that helps. Can't see how it would as the one in there tests fine but what else can I try?
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
get the crank sensor from the dealer
aftermarkets are all crap.
aftermarkets are all crap.
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
did you use the stock flywheel?
aftermarkets have a known issue of the windows being off time, and the diameter of the tone ring slightly too small, causing too much air gap for the sensor.
aftermarkets have a known issue of the windows being off time, and the diameter of the tone ring slightly too small, causing too much air gap for the sensor.
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
Same flexplate/flywheel that came off the motor when it drove in the shop. 
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
So tried yet another cps, no change. When I turn the motor over its not registering any rpms on the tach.
What could cause that? Help!
What could cause that? Help!
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
Well... I give up. I've exhausted every thought, clue, and gesso I could come up with. Have to start looking for an electrical guru to come figure it out. Can't wait to see what that will cost...
jeepdreamer
NAXJA Forum User
- Location
- Ft Myer, Va
Yup.. tried that and found nothing. Actually did it twice because we started and found no 5v immediately for the cam sensor. Sweet!, right?
Nope.
We forgot to plug the black back in the cps. Doh!
Only thing I haven't messed with is the clockspring thing. Can't say I honestly understand what it is or how It could effect things...
I'm just hopeful the guru will find it tomorrow so I can fix it and move along.
