Please help me with my diagnostics...

Hi

I did a search for No Bus and wont start and didn't quite find what I was looking for.


Went to start the XJ, a 2001 automatic, to go to work on Thursday and it wouldnt start. Plenty of juice but no start. Just cranked and cranked but no start!

The check engine light has been on for two years. Usually telling me I have a slow idle.

Lately, the last couple of months, its been slow cranking. Sort of like an old car with a distributer that's backed off to much.

The odometer says "no bus."


I'm guessing it's a crank position sensor?

Thoughts?

Thanks!


Chad

"No Bus" on the odometer and a crank - no fire is typically a crank position sensor. By chance, when you turn the ignition to the on position, are you getting a reading from your volt meter, or is it showing nothing? This seems to be another clue as to a crank sensor that sometimes happens on late model Jeeps (seen this happen on both Grand Cherokee's and Cherokee's.)

You can verify this by unplugging the sensor (located on the transmission bell housing, about the 1 o'clock position if you're facing the front of the Jeep), and checking the resistance across two of the 3 pins on the harness of the sensor. With the little tab for the vehicle side connector to clip onto facing UP, the two pins you're looking for are the middle and the right ones if I remember correctly. If it reads open (no resistance), the sensor is bad. If it gives you a resistance reading, the sensor is good.

Crank, no start and "NO BUS" generally indicates a crank sensor shorted to ground.

In addition, if you try and hook up a scanner/reader it won't communicate with the PCM.

Quick and dirty check: UNPLUG the crank sensor, key ON--do the gauges work? If yes, replace the crank sensor.

LYKOS said:

The check engine light has been on for two years.

Click to expand...

Chad,

Yup, the #1 cause of NO BUS with engine not starting is the crank sensor. Theoretically, any of the 5 volt sensors could short and pull down the bus, but the crank sensor is the one most prone to this type of failure.

BTW, this is not likely to be related to your check engine light. I always recommend chasing and resolving a check engine light. Even if it is not that serious, the next time you have a problem, you have a more complicated troubleshooting process as the original problem may or may not be related to your most recent ones.

To anyone out there in land with a check engine light. Pull the codes and post the EXACT code number(s) here for comment! Use the technology provided to you by your Jeep. While the OBD system oftentimes needs some interpretation and may not tell you exactly what component is faulty, it WILL point you in the right direction.

I went ahead ad bought a CPS in hopes trhat it resolves the problem. If not, at least I have a new CPS.


Given the fact I'm 6'2" 300 lbs and have hands and arms proportionate to my size (don't fit in tight spaces) do any of you have any suggestions on how to remove and replace the CPS?

I looked at it this morning and couldn't get my hands in there to get to it!

Here is a link to a pretty good article on replacing the crank sensor... and below it is a link to another thread on replacing it.

http://www.go.jeep-xj.info/HowtoCPSchange.htm

http://www.jeepforum.com/forum/f11/crank-position-sensor-write-up-197260/

I just did mine a week ago. I unbolted the cross member and let the tranny hang down. Use a jack. Then with a long extension and a knuckle you can get at. I am built like you and had a friend helping me with skinnier arms. With the exception of breaking one of the cross member bolts it was a pretty quick job. Drilling out the bolt and taping a new hole took the longest.