RANG7R

Hello, this topic has more then likely been discussed buy my searching has led me astray on this forum.

I recently acquired a 1999 Jeep Cherokee Classic 4.0L 4x4 153 000 miles automatic. It was hit lightly on the front end, mostly cosmetic damage, it still ran when I brought it home, ran well, and rest of the truck is in good shape.

I have had it for about 3 weeks, had it up to the body shop getting some mild frame straightened and a new rad support put in and she ran good then too.

Since she came home she got a little cranky to start, I assumed from sitting for about a week. But on Monday I went to start her and put her on a friend's trailer to take it to my uncles shop to finish up the work on her and the battery was dead, so we boosted her, and accidentally the booster cables got hooked up backwards somewhere along the lines of boosting her and she made a pop and sparked. But we switched the cables around and she started but was cranky again and didn't want to idle on her own for about a minute. I had to boost it again when we got to the shop and she ran a little cranky again but got her self off the trailer and into the shop on her own power.

So I started working on her and got the front end all on her again, ripped the blown air bags out and replaced with good ones, and put a new rad in it. Hooked the freshly charged battery up in her and went to start her. All she would do is turn over, she would buck a couple times but she wouldn't run. The ASD relay will constantly buzz, and the NO BUS indication came on the odometer. This had never happened before she got to the shop.

I assumed the NO BUS is from a fried PCM, but if the PCM was damaged why did she start and run after the booster cables were hooked up backwards? Other forums say that the Crank Position Sensor will cause her not to have an injector pulse or fire, which would explain why she isn't starting/running but does not explain to me why the NO BUS is showing.

The NO BUS from what I've read can be caused by something as simple as the gauge cluster not having a good connection, which would've made sense cause I was reefing on the dash a little bit to fit the passenger side air bag in and the new dash pad that sits up by the windshield, but tonight I ripped the gauge cluster out of her and made sure she was sitting tight with the connectors. Still received a NO BUS message and no start when I tried her.

Whatever the problem is she has me stumped and I'm not even sure where to start. I have access to another Cherokee the same year as mine with the modules still in it but it has been sitting for a while and was in a roll over, I got all my parts off of it. I would be willing to try another module but I heard that dodges will instantly fry the problematic module if you try one from another vehicle???? I also would like to try a new CPS.

Any help on this would be so greatly appreciated!!!!!! I've been losing wayyyyyyy too much sleep over this. Even if someone has a link to other threads that cover this topic or anything of the sort.

-Matty (RANG7R)

tjwalker

There are 2 types of NO BUS conditions.

#1. A no bus appears on the dash, but the engine runs fine. This is almost always a dash cluster problem

#2. A no bus appears on the dash and the engine does NOT run. This is your problem.
A good majority of times, it is a failed (shorted) crankshaft position sensor causing this. Theoretically, any 5 volt engine management sensor can short and cause this problem, but the crank sensor is the most suspect.

Try this simple test. Get under the vehicle and remove the connector for the crank sensor (on transmission bellhousing). NOW check the dash. If the NO BUS is gone, you have confirmed that the problem is the crank sensor. Try this with each of the 5 volt engine management system sensors.

BUT, knowing the history of the cables being put on incorrectly, this could be a damaged computer as well.

RANG7R

I will try un hooking the CPS and see if she still displays the NO BUS.

But if she is a module blown, why did she start after the cables were reversed? In my mind and experience, anytime polarity was reversed she instantly fried the module and she won't start. I don't understand why I still got two starts out of her afterwards, even if she was fussy too get going.

Do you have any access to wiring diagrams for these jeeps?

thanks for your suggestions!

RANG7R

I also still have power to all my fuses in the fuse block under the hood, and all my interior functions still work, radio, windows, locks, interior lights, key in ignition buzzer, indicator lights come on the dash, etc.

Cherryokee

X2 on Tjwalker's advice, with one minor correction. The connector to your CPS is not underneath. It's on top of the intake m'fold just behind the TB but before the back end of the m'fold. The other "working" stuff you mentioned doesn't matter and are not critical items in this case - they are less sensitive to reverse polarity power and were not in use during boosting/starting. Also, you might not have outright blown those sensors but electrically overstressed them to the point that they are now marginal at best - might work a few times more then pffft - nothing.

RANG7R

How do you accurately test your CPS? If I check for resistance in the connector what should my reading be if it is healthy?

tjwalker

Here is a thread with the information on testing the crank sensor.

http://www.jeepforum.com/forum/f11/c...ailing-639123/

The crank sensor can be disconnected at either of two places. Directly at the sensor itself, or under the hood near the firewall / #6 injector, there is another connector.

Good luck!

RANG7R

I might be onto something but I'm done playing for the night, I'm leaning more towards the PCM or other modules. I changed the rad support and there was an unknown sensor on it (I'm assuming an impact sensor) and I left it disconnected. Sooooo I'm assuming the air bag module (which is on the bus route) isn't getting all of it's information or completing the power cycle, causing it to not allow the power go through all of the other modules, which explains why I'm not getting power or ground at my PCM connector in the bus (+) and (-) pins on the gray connector (I have a connector diagram). It's just a shot in the dark but I'm gonna try to find out which one of my connectors that needs a home fits her. If anyone had a wiring diagram for such a mess would ya's up load it PLEASE

RANG7R

got er figured out boys, just a bad ground from what I can see

Michael Hane

What was the ground that you found to be the problem?

Michael Hane

I am having the exact same problem on my 97 Cherokee and I have replaced the crank sensor and pull the dash to check the connection and it still just cranks and won’t start but says no bus on the odometer.

Noah911

Michael,

Are the cluster gauges working any at all? Or, is it just the fuel gauge not working to display information?

(edited to add):
This is a very old thread you are using to post about the problem you are having with your Jeep. I think it may serve you better if you begin a new thread about it.

Hotroddinlogan

Its definitely one of two things, you computer, or some loose wires.

Ethan.n

I had this same code pop up a handful of times. The car would start just fine, idle and run perfectly for a few minutes then it would happen- "NO BUS". It eventually went away and never came back. Is this something I should be more concerned with? I haven't bothered looking more into it because I haven't had an issue since. Is there any possibility the car's motor would cut out while driving?
Thanks,