" No Bus " on instrument panel

i did a quick search and didnt find much. im at work so i dont have tons of time to dig around so im hoping someone here has the answers i need.

2000 xj with 124,XXX miles auto 4.0

no problems untill about 45 minutes ago. this morning i came into work without any issues at all.

i went out to my jeep at lunch and tried to start it and at first it wouldnt start at all. after trying again, it was very hesitant and i had to give it some gas to get it going and keep it from dying but i did get it started once.

during this short time that i got it running, the check engine light came on and the instrument panel read "no bus." i took my foot off of the gas and let it die. i turned everything off and took the key out and then tried to start it again with no luck.

so as of right now it wont start and the check engine light is on.

i cleaned and checked the battery connection and i also unplugged/plugged in the instrument panel making sure that there was a solid connection and this didnt change anything. (i was told that the problem may have been a communication issue due to a bad connection)

help. please.

it just seems like one thing after another lately.

Thanks in advance.

Castle.

I agree with hubs97xj on this.

There are two types of NO BUS conditions.

1. You see NO BUS and the engine runs fine (usually a cluster connection issue or ground issue)

2. You see NO BUS and the engine doesn't run

Your situation is #2, so the crankshaft position sensor is most suspect. It can happen when the crank sensor fails in a certain way (shorted) and jams up the computer bus.

Theroretically, any of the 5 volt sensors could do this, but the crank sensor is by far the biggest suspect.

What I usually do to confirm this is to unplug the connector to the crank sensor. Now check your dash. If the NO BUS message is not there any longer, you have proof positive that the crank sensor is the culprit as by removing the connector, you have taken the crank sensor off of the computer bus. I'd try this.

I think the computer should be reprogrammed for option #2 - should read "BUS" to suggest an alternate way of getting home while your XJ awaits repair.

BrokenSockets said:

I think the computer should be reprogrammed for option #2 - should read "BUS" to suggest an alternate way of getting home while your XJ awaits repair.

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im at my wits end here. idk what to do.



i was able to have my sister give me a jump and some how limp it home. i didnt have any no bus code or check engine lights come on at all. everything seemed fine.

i got back into thornton (i work in boulder) and went to autozone to have them test the changing system just to see what they said and after turning it off, i couldnt get it started back up again. my battery is/was completly fried but even when trying a new battery i couldnt get it started.. not even with a jump.

its like its hardly getting any power at all the dome light barely comes on and the only light that will come on in the cluster is the "brake light" which is very very dim. it wont even try to start. not even a little bit.

Ok, with a good battery and it won't crank? I would suspect the main cables and/or starter-solenoid, but because you have bad electrical in the cabin I would suspect your cables are the main culprit.

Do a voltage drop test on the cables: http://www.aa1car.com/library/voltage_drop_testing.htm

Did you test the CKP yet? Did you unplug it to see if the Jeep cranks, but doesn't start? Did you look to see if the "no bus" goes away with the CKP unplugged?

I'm not disagreeing with Joe, but my junk has been in the salt and snow for it's entire life, and the grounds are in great shape. I've seen an older Jeep with a bad CKP and a bad starter, but given the no bus, no start, and randomly starting and driving fine, I wouldn't think it's a bad connection issue. Either way, some simple testing or half an hour with a DMM will tell you what's good and what isn't.

no, i havent checked the CPS by disconnecting it yet but i'll give it a try after work today.

i havent seen the no bus code come on aside from the one time at lunch yesterday. the problem now seems to be that i'm not getting any power.

my battery terminals are pretty corroded but after cleaning them there was no change. should i replace the cables?

You very well may have two problems here.

1. Intermittent NO BUS problem (suspect crank sensor here) The NO BUS problem though is not going to cause the electrical symptoms (dim lights and no crank) that you describe.

2. An electrical problem yet to be determined. If the battery is new and fully charged and the dash lights are still dim and you have a no-crank, I would freshen the engine GROUNDS first thing. You could even temporarily add a new ground cable from the battery and if that allows your electrical system to do its thing, you have confirmed a ground problem. Could be something else but this smells of a connection/ground issue of some sort that is most likely not serious.

i still have not seen the no bus code since the one time it came on at lunch the other day.

like i said, i some how managed to get it back to AZ in thornton where it died again. BUT, i was able to get it started again last night and get it home. after i got it running, i had AZ check the battery, alt and i hooked up their OBDII scanner to see if there were any code or to see if it would atleast communicate with my jeep. the scanner said "pass. no codes found" or something.

i bought a new battery (which didnt make a difference but my old one was dead and couldnt be re-charged so i needed it anyway.) and i replaced the pos and neg battery cables. after doing the cables i tried starting it and........................ it worked

so i had a bad connection somewhere in all that mess of corroded nasty junk and replacing the cables fixed (helped?) that. it's started every time without any problems since and i was able to drive it in to work today.

i still dont know whats going on with that no bus code though.....:dunno: