2002 Liberty Limited No Bus Error: I need help!!! - JeepForum.com
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post #1 of 18 Old 10-27-2017, 11:08 PM Thread Starter
themorganshome
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2002 Liberty Limited No Bus Error: I need help!!!

I'm new and posted this in the intros, but i think this is the more correct forum. Hello everyone, I'm new to the forum, and live in the Seattle area. We purchased in April this year a 2002 Jeep liberty Limited. It has 200,000 miles, but not the original engine, plus the head gasket has been replaced at the beginning of this year too. However, we are have LOTS of No Bus error drama. HELP! We're getting desperate! Let me explain.

1) Car running fine, then all the lights on the dash light up... and then all gauges stop working, and then a No Bus error pops up.
2) Even though the car still runs, within a day, the car turns on, but turns off within 5 seconds. Came here to Jeep forum, and read lots of ideas of what to try. The Following is what we tried so far:
3) Assumed the Cluster was bad (at least that's what the dealership simply thought by looking at codes., so we purchased a used Cluster with only 100,000 miles on it. Within 10 miles, the exact same problems/No Bus error/car shuts off seconds after starting when the issue shows up again, one day later.
4) Replaced the PCM (Powertrain Control Module) with a refurbished one. Jeep dealership programs it and assigns our VIN # to "newer" PCM. We put in the PCM, the car now runs, but No bus code remains. I drive the car home to our home to keep trying options.
5) Replaced battery with new battery. Didn't seem to fix anything.
6) Have cleaned both the male and female parts of the connections on the back of both the old cluster, and newer cluster. That didn't work or improve anything.
7) I've watched about 40 YouTube videos with guys trying to fix the same problem, but most of the fixes I've tried, including above steps. No change. Car won't stay started and No Bus code issue remains.
8) I've visually looked at EVERY fuse in the dash-fuse box, and the engine fuse box. Every fuse "looks fine," but I'm about ready to replace every fuse, noting that several have said there could be a problem with one of the fuses, despite it all.
9) I have 16 year old daughter who is about ready to scream because this car, which she drives, hasn't been working for more than 3 weeks now.
10) Any other thoughts out there.??? I'm willing to try anything... It's disconcerting when the jeep dealership hasn't been very helpful, other than flashing/programing the newer PCM and installing such.

HELP!
Frustrated in Seattle!!!

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post #2 of 18 Old 10-28-2017, 01:21 AM
Billwill
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"No Bus" errors are very difficult to find. The Bus on the 2002 models is a serial PCI bus that runs around the whole vehicle....it sends and receives serial data to and from various components.
The cluster is one of the components serviced by this bus but a short or break in the bus anywhere else along the PCI bus line.....from the Data plug below the steering wheel to some Radios....can hang up the bus.
In other words the cluster is merely reporting an error on the bus but the cluster itself may not be the culprit!

Does the Jeep actually start and run or does it start and then shut down after a few seconds? Do you get an amber "Key" symbol flashing or constantly ON showing on the cluster.

You can download the 2002 KJ Service Manual here....gives some information on how the bus works and has the Wiring Diagrams...section 8W... where you can see where the bus goes...the bus is a single wire surrounded by a sheaf of wiring much like a co-axial cable used on TVs.

Look at section 8E of the documents..."modules" and read up on the BCM which I believe is where the PCI bus is generated. The BCM sits on the reverse side of the internal fuse panel. I would consider replacing this module but some re-programming is needed for some functions ie. Hazard lamps flash when locking the Jeep etc. These are minor issues...the Jeep should run! There is a small unit the size of a ciggerete box plugged onto the BCM....retain the original unit as this is the receiver for remote locking/unlocking.


The trouble with the PCI bus used on early KJs...later KJs changed to a combination of CAN, SCSI and some PCI busses...is the fact that it is very difficult to find an off the shelf Code Reader or computer APP capable of reading the PCI bus!. So it is up to the Dealers to use their code readers to read the bus but of course if the bus is damaged somewhere then even that will not work!

My 2002 Export 2.5L CRD has the ECM...PCM on a gasser....made by Bosch. Even the Bosch Dealers here in SA shake their heads when I ask them to pull some codes out of the ECM!

So the possible causes for a bus error are:

The internal lead on the bus is shorting to the metal sheathe around it.
There is a break somewhere in the bus cabling.
The bus is shorting to chassis/engine somewhere.
A bad connector on the bus not making good contact.
One of the components plugged onto the bus is pulling down the bus.

You cannot measure the bus with a Multi meter as it is a stream of serial data...you need an Oscilloscope or a capable PCI bus reader.

So you need to study the wiring diagrams from my link to find where the PCI bus goes. With battery disconnected you need to one by one pull off the connector connecting the bus to a component...the cluster for example. Measure with a Multi meter set to Oms the resistance between the center wire and the outer sheathing. If it shows a dead short then continue pulling off the bus connectors from all components until the short disappears....this is the component pulling down the bus.

You also need to measure the continuity of the center lead from point to point. For example measure from the cluster to the PCM where you will see this strange looking wire going.

http://www.colorado4wheel.com/manuals/Jeep/KJ

2002 2.5 Export CRD Manual 5 speed.
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post #3 of 18 Old 10-28-2017, 02:21 PM Thread Starter
themorganshome
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Thank you very much and you've given me a lot of homework to do and sleuthing to do on this car. To answer your question,
On Monday the dealership Flashed and reprogram the refurbished PCM that they installed. I drove away from the dealership with the cluster saying no bus, but it was drivable at that moment. After 5 miles, suddenly everything started working, guages, mileage, and everything else, except the low tire air light was on.

15 miles after that the airbag light came on. Then about 10 minutes later, the no bus error popped back on, but it was still drivable, but no guages, along with it every warning light was on too. Eventually the key symbol light turned on permantly, but I didn't think much about it. The next morning, even though the no bus error was on, my daughter drove it to school. After school she could turn the car on but but it went back to turning off within 5 seconds and I now have a very frustrated 16 year old again. So the current status is a car with a no bus symbol, all the warning lights on, and the car turns off within 5 seconds...
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post #4 of 18 Old 10-28-2017, 02:44 PM
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questions - maybe a clue.

vehicle is STOCK?
Any recent work repairs maintenance?
The dealer you mention is a jeep dealer?
any issue before headgasket?
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post #5 of 18 Old 10-28-2017, 07:47 PM Thread Starter
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Update: We went just now to the high school to have it towed back to our house, but my wife popped in the key, it started and stayed on, and it didn't give us the "No Bus" error, and the gauges worked.. but there are other things going on.
1) check engine light stayed on.
2) low tire pressure stayed on.
3) airbag light popped back on.

So we drove it home since it was running.

A symptom: Within a few days of us purchasing it in April, the airbag light would come on and off randomly almost on a daily basis. Eventually, the Airbag light would not turn off and then the no bus issues started haunting us 3 weeks ago.

In answer to the most recent uestions:
1) Is the vehicle stock? Well...we did the carfax, and it listed a new engine somewhere before 50,000 miles because of an auto accident. Technically the car is at 200,000.
2) Recent major work ?: Yes, I had a non-dealer replace the head gasket in July via a warranty. Airbag light was going off and on both before and after that new head gasket. It ran well (despite the airbag light) all of August and September, then October and the No Bus errors started happening.
3) The dealership that wasn't very helpful was an actual Jeep dealership. The reason being was since the car is 15 years old , you can almost not find a brand new cluster or a new PCM out there, unless they're used or refurbished. They didn't want to spend hours going through all the electric possibilities, given that it's a mystery... (They felt it would be financially irresponsible of them to me) and they also hoped that my problems would be fixed by inserting a referbished PCM. Honestly I'm kind of glad I have the car back because I don't mind spending the hours going through the electrical thingd that have been suggested already....however I will take suggestions from anyone. Money doesn't grow on trees... so come Monday, I start going back at it.
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post #6 of 18 Old 10-29-2017, 02:43 AM
Billwill
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If you look at the wiring diagram page 8Wa-43-2 you will see that the airbag control module does have the PCI bus going into it....a Yellow/Violet/Orange wire....so it is probably again related to a problem on the PCI bus. I think that this PCI bus will probably be the same wire colors throughout the vehicle...maybe changing to the single wire with a sheaf around it as it enters the PCM....this is what I have seen on my 2002 Export CRD.

Have a look at the diagnostic port where a scanner would plug in....same wire should be present there and so on for all the other components served by this bus.

The only way I could think of diagnosing the problem....other than replacing the BCM module...is to find every point where this PCI wire plugs into and with the battery disconnected...measure continuity from point to point of this wire and then with every known PCI connector pulled out...check that there is no short between this wire and chassis....the cable could be fraying to chassis somewhere.....a lot of work!

The trouble with the wire harness on the KJ is that they do not connect components together by the shortest possible route.....the main harness goes all the way around the engine bay like the Beltway in Washington. To connect components located 18 inches from each other the harness travels around the engine bay for about 8 feet....going through some connectors along the way. This harness travels under the radiator through a metal channel...at least it does so on the CRD...not sure about the 3.7 Gasser!

After a front-right collision with my Jeep in 2007 I had to trace 7 faulty wires that got damaged inside this metal channel up front. Only way to diagnose these was to disconnect every component on a particular line.....including splices...and then measure the suspect wire for a short or semi-short to chassis when it should be floating in thin air! Then I had to cut off the ends of this wire...including splices and replace the complete circuit with brand new wires....taking the shortest route.....the seventh wire that I traced was only done about three weeks ago!

Fortunately I am a qualified Electrical Engineer with many years experience in Mainframe Computers and Robotics so I could do this... retired but still able to diagnose problems.

I would first try replacing the BCM before trying the above procedures!

2002 2.5 Export CRD Manual 5 speed.
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post #7 of 18 Old 10-29-2017, 10:03 PM Thread Starter
themorganshome
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Thanks BillWill For all your suggestions. I certainly will be doing lots of sleuthing this week with your guidance including most likely replacing the BCM.

As another update... this afternoon after church, I had my daughter sit inside her KJ and tried turning it on, and it went back to the whole "turn on for 5 seconds and then turn off with a no bus error." It's almost like daily, depending on what the temperature is outside, or the dew point, or who knows what.... it can't decide if it wants to:
1) Stay turned on without the no bus error (but with the Airbag/Low
Tire Pressure/check engine lights on), Or...

2)Flat-out not run longer than 5 seconds (..it then turns off) with the No Bus error showing, (...And every gauge not working and, warning light lit up like a Christmas tree.

A further observation: The other night with the "newer cluster in," after I locked that door... the little red light on the dash would flash as if there's some sort of anti theft warning device installed. Now that light isn't happening at all either... both last night when we didn't have a bus error, or tonight, when we do have the bus error. (It may be nothing, but at least I wanted to share such.)

Ok, so I'll keep you posted. Over these next 5 days, I'll be sleuthing and trying anything. If you have any other inspiration, or anyone does, please reply and offer suggestions because I really want don't wanna go out and buy another car because this one is esentially not working for us.
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post #8 of 18 Old 10-30-2017, 05:02 AM
Billwill
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Yes this is a very difficult problem to try find....you may end up replacing virtually all the modules in the Jeep at great expense while somewhere the Bus wire is intermittently chafing through to chassis/engine!

A good Auto Electrician may be able to trace the fault if you give him a copy of the wiring diagrams but that may take a long time/expense.

A bad grounding point on the chassis can also cause weird problems....an old Jeep like yours and mine....escpecially if you are in a snow/salt road area can have major damage to the grounding points.

The wiring diagrams has a section where all the Grounding points are identified...most times with pictures. So if you are not getting anywhere check these grounding points out!

Start with the main grounding points of negative battery lead to chassis and the grounding points...two for the 3.7 L...grounding the engine heads to chassis.
Also check the battery terminals and your battery...low voltage to any of the modules causes weird problems.

I will go through the wiring diagram for your jeep and try to list all points where the Bus goes to....then you can try disconnecting all the points and with a cheap Digital Multi meter start doing some measuring for continuity/shorting of the PCI Bus circuit....may include cutting some wires, measuring then soldering them back together.

2002 2.5 Export CRD Manual 5 speed.
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post #9 of 18 Old 10-30-2017, 06:59 AM
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long posts get confusing - just old age I guess.

thoughts
If the air bag light is ON - need to read the code.
If the CEL is on or has been on also read code.

I wonder what jeep found as to which item is not on BUS during no bus indication.

Right now I am thinking a power problem, a ign switch or replay not feeding all modules.
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post #10 of 18 Old 10-30-2017, 07:14 AM
Billwill
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Check page 8Wa-18-1 in the wiring diagrams....shows where the PCI bus goes.

Also shows that Fuse #33 on the interior fuse panel is involved....check and re-plug that fuse.

I agree with jtect here....did the Jeep Dealership find anything with their scanner?

2002 2.5 Export CRD Manual 5 speed.
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post #11 of 18 Old 10-30-2017, 11:08 AM Thread Starter
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On visit 1 to the dealership), They simply only came back that I had a bad cluster to start. So I went out and got a "newer one" that had only 100,000 miles on it and plugged that one in (yes, I have this funky sticker affidavit now on the inside of the door panel stating when the mileage change...). The newer cluster immediately had the low tire pressure light turn on, although all 4 tires pressures were just fine. The cruise control also didn't work. 19 miles later... I hear a chime and suddenly the airbag light turns on. 5 miles after that, another chime sounds, all the warning lights pop on and the gauges stop working. We parked the car at her house.... a couple hours later we turn the car back on in a won't stay on after 5 seconds

We have it towed to the dealership. (Visit #2). The guy eventually tells me that their data is showing the pcm is toast I need a new refurbished 1. I went out and got 1 and they installed it. The rest of the story is listed earlier in this thread.

What is (amusing/not amusing) now, is that based upon it being cold or warm outside, or the dew point, or who knows what... it will either start and run with various warning lights on, or it turns on for 5 seconds and gives us the no bus code.

I'm sorry I've been so detailed and long winded in all of this,... I wanted to give every symptom happening in case someone has an "ah-ha" moment, and has a great suggestion for something I should try. I will be trying all of your suggestions this week and I appreciate any help anyone has/will provide. I really mean that. pI don't mind working on cars, but it's not my forte..., it something more I try to save some money with, with here and there. But when it comes to electic issues, it's very frustrating...and we find it ironic it's Halloween time. My 16 year old daughter thinks the car is now possessed because it's random symptoms change from day-to-day almost.
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post #12 of 18 Old 10-30-2017, 04:34 PM Thread Starter
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Update: My neighbor has a code reader and 2 codes are listed: P1698 & P1686. I'm guessing the second code P1686 has to do with starting and turning back off, as if i don't have the correct key FOB.... Any thoughts anyone?
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post #13 of 18 Old 10-30-2017, 06:34 PM Thread Starter
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Fingers crossed that it may be fixed...! So the car wasn't staying on.... No Bus code of course, and my neighbor's scanner was giving me two codes... So i did a Bing.com search, using different words to see if I got any other ideas... well, a guy in Idaho, on a diff forum, suggested that ".....
I have seen a radio shorted internally take the BUS down. A really simple way to find the cause is to remove each*fuse one at a time, try to start, and reinstall*fuse*until the message goes away and the vehicle starts.*

Just go to your*fuse*box in vehicle and under hood, remove a*fuse, try to start, and reinstall the*fuse*to it's original location. Repeat until the vehicle will start and run. This is standard practice to isolating the circuit that is causing the BUS to malfunction."
Well I did that, but did one better. Each time I took out a fuse , I notice that ALL of them were gunky/blackish and were oxidized on the metal a bunch,and so I took some really fine sandpaper and scraped them all shiny... and then put them back while doing the above suggestion. As I went along doing this, it started working after I cleaned-up and shined the three fuses that went ti the BCM, the Cluster, and the SKIS. These were fuses in the druvers side door panel. Now, the car is running, and all the warning lights are off, except the low tire pressure light. (This could be because the Jeep dealer guy insisted I get a cluster from a 2004 KJ instead of a 2002. I don't know if my 2002 even has a tire pressure sensor....) Anyways, I'm holding my breath, and we'll see what happens tomorrow... If the cold weather or a cold engine makes any difference since I got this working on a bright fall of Sunny day...) All fingers are crossed....
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post #14 of 18 Old 10-31-2017, 01:32 AM
Billwill
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I doubt that the 2002 KJ came with tire pressure sensors.

Maybe refit your original cluster if you still have it?

Anyhow at least it looks like dirty fuse connections were your problem.....good news!

2002 2.5 Export CRD Manual 5 speed.
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post #15 of 18 Old 10-31-2017, 07:12 PM Thread Starter
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I spoke too soon... I got all excited that possibly all was well after cleaning/replacing every fuse... and then the same issues happened. Either one or two error codes occur:

P1698 and P1686. I've been told that the P1686 isn't the main problem. After looking at the service manual of what to do, and it's flow chart (for p1696), that either i have a short/messed up harness, or I have a bad TCM. (..based upon not being able to clear the codes with a scanner, thus the conclusion from the service manual...).

To me the easy thing would be to get a newly flashed refurbished TCM.... but maybe I need to check every wire coning out of the TCM. Should I check the grounds coming out of it?
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