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2000 XJ Another No Bus... No Start

Night0wl

NAXJA Forum User
Location
Virginia
Ok XJ pros, I need your help here. I have done my due diligence and researched as much as I can and tried everything I know to fix this problem but it has not been resolved.
Background: 2000 Jeep Cherokee Classic, 4.0l, Automatic, 165,000 miles (Does not have the chip keys, immobilizer system. My keys are black and they are original)
A few days ago I tried to be the good neighbor and help my neighbor across the street fix his tandem axel trailer that had a pigtail pull loose after he went around a turn due to not enough slack. His 7 pin trailer plug on his 4runner wasn’t working so I told him I had one on my Cherokee we could try. ( I installed this years ago. Hooked up everything but the aux brake line) He was in the back with the pigtail plugged up and I went up and turned the lights on. When I got to the back I saw he was holding one of the trailer wires and jumping from blade to blade on the open pig tail. Wouldn’t you know it a spark and my drivers side tail light went out. I didn’t know he was doing this, I would have been using my meter! We blew a fuse right? Yes, so the 10 amp fuse on the passenger side kick panel #7 I believe was blown. Replaced it. Lights worked. Fixed the trailer. Go to move the Jeep. Cranks but no start!!!
Start investigating. No gauges. 20 seconds after the key is turned to run, “NO BUS” and the engine light is on. Everything else works, lights, blinkers, radio, blower etc. Start checking more fuses. Inside kick panel and PDC. No other fuses blown. Wiggle the shifter, put it in neutral.(will not crank in D or in gear so I feel NSS is working) Still nothing. OBD2 Scanner will not connect. Acts like no fuel. Fuel pump is not coming on. No fuel pressure at Schrader valve. Got online read tons of articles. (here and other places) unplugged the CPS like suggested as well as other sensors, and still no gauges and NO Bus is still there. Left battery disconnected for half an hour. Pulled instrument cluster out and examined. Cleaned contacts etc. Re-seated and insured positive connection. Cleaned, steel brushed and reseated all ground contacts while waiting No go. Tested the CPS. It showed low resistance so that tells me it is bad. Ran to Advance Auto and picked up a Crank Position Sensor (sorry, dealership is no where near me and it was late) $97 later got it installed. NOPE! Disconnected main wire harness at drivers side kick plate. Electric contact cleaner, dielectric grease… Still the same problem, so I started at the ECM, disconnected, cleaned contacts, dielectric grease. Recheck. Still down. Pulled ECM schematic and checked incoming and outgoing values. 12V present from bat, 12v present from ignition, 5V output present to sensors. (actually is 6V)
Here is where I start to see an issue. Tested voltage at the sensors themselves. Mass Air Flow sensor only showing 3V, one of the 02 sensors only shows 4V. Unplugged Cam Shaft Position Sensor. Still not working.
So I have something bleeding the voltage. I disconnected every sensor I could find or knew of. Still same problem. Went to the PDC and looked at the relays. Fuel pump relay is not coming on. Swapped that out with another one. Didn’t make a difference. Checked voltage at the relay socket. 12V is there from the power side but no 12V signal to energize the coil. Did the same test on the ASD relay. It happens to be the same relay as the horn relay inside the passenger side kick panel fuse area by the way. It has 12v power as well but no 12V signal to energize the coil. So that explains why the fuel pump is not running. But why no signal from the ignition. The ECM has signal from the ignition. Inline ignition switch fuse is good.
I cannot find a wiring schematic telling me where the wires go when they leave the ignition switch. I think if I can find the sensor that is bleeding the power on the 5V side I can get the no bus to go away but what about the ignition switch power to the ASD relay???
I am at a real loss and feel like I have exhausted most options. I haven’t changed the ECM because I don’t think that is the problem. It is functioning with exception of the lack of communication and “NO BUS”
Can anyone help me with proper wire diagrams or with something I may be missing?
I really appreciate any thoughts or ideas. I know this “NO BUS” issue has been gone through many time and 90% it is the Crank Position Sensor. But my new one meters out correctly and with it unplugged it doesn’t change anything. I feel I have hit every sensor I know but the problem could be in a line going to the sensor itself.
I think the foul up by my neighbor contributed but then again it could just be coincidental.
Any thoughts or suggestions or help would be greatly appreciated. Thanks
 
No Bus and no communication with a Trouble Code reader is likely a short or open on the CCD Communications Bus. Bleeding voltage make me think short circuit. I suggest spending $7.95 at Pacific Coast Manuals for a genuine Jeep Service Manual.

One at a time unplug each of the 5 volt sensors and re-check for No Bus and no communication each time. Remove the horn relay, a short in the clock spring circuit can feed 12 volts from the horn circuit to the TPS.

Read this thread on another Forum -> http://www.cherokeeforum.com/f2/gauges-no-ccd-bus-strange-unsolved-205151/
 
Thanks Tim!
We will give those a try. I did remove the horn relay previously but that was it was the same relay as the ASD relay and I wanted to check to see if the ASD relay was bad.
 
pull the back cover off the pcm, and check for burnt/distorted connections on the circuit board, sometimes no bus is caused by a bad pcm....

also check all chassi grounds, and pcm grounds....
 
I actually did pull the computer and took the back cover off.
I didn't see anything that looked like a bad solder connection.
But then again I didn't have it in the garage under the shop light. I will check that again. It just seemed to me that the computer was working as it was putting out signals like it is supposed to. There are 4 black wires grounded to the fender well right below the computer coming out of the wire harness. I did clean those up and wirebrushed everything and set them back in place.
Are they the actual ground for the computer?
 
Well, we are still in the same boat.
Haven't gotten the schematics just yet.
According to drawings I have seen the ASD relay should get its signal from the start switch.
Does anyone know if this signal wire goes through anything else first?
From what I can tell this is part of my problem.
The ASD relay is not getting the signal and therefor is not turning on the components after it.... Fuel pump etc.
I feel like I need to start here. I cannot find an issue with any of the sensors yet. I know it is a possibility that the problem is with a feed wire going to one of the sensors.
 
No-Bus means there is a problem with the communications between the PCM and one or more of the 5 volt sensors. If the PCM does not see the correct data from the 5 volt sensors, it does not energize the ASD.

The Service Manual has complete trouble shooting if this/do that charts, the exact test procedures, and wiring schematics. Without it, all you are doing is poking at random wires.
 
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Tim,
I guess I need to hit up Pacific Coast Manuals today then!
Thanks. I thought the ASD was energized by the ignition and not the computer so that is why I was not continuing to look at the PCM.
I will keep everyone posted on the progress.
 
I went and downloaded a manual from Pacific Coast Manuals.
While it is good and in depth it did not tell me the direct connection to the ASD relay coil.
I did find a wire drawing online that shows it coming from the ignition somewhere. But, it is not specific enough to troubleshoot.
The ECM has been taken off and carefully looked at. I see no signs of cracked solder joints or damage to the board.
If I go to a local used parts yard (should I say salvage yard) how are they to know if the computer matches up with my XJ or not?
I do not have the immobilizer that everyone talks about.
I am still at a loss and replacing this ECM seems like the logical thing to do if you say the signal for the ASD (relay coil) comes from the ECM.
 
The logical thing to do is to test each of the 5 volt sensors, and to check their wire harness for continuity. Always start with the basics, instead of replacing random parts on a guess. Remember to ALWAYS use genuine Jeep sensors. Newly installed cheap parts can be the problem, and not the solution. Most auto parts stores sell cheap crappy Chinese "Lifetime Warranty" parts that are often out of specification, or even failed, right out of the box. Many times they have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured with genuine Jeep repair parts. Cheap parts are cheap for a reason.


Did you perform the test in post #3 in the linked thread ? http://www.cherokeeforum.com/f2/gauges-no-ccd-bus-strange-unsolved-205151/
 
Well, hopefully I can take this "cheap" Crank Position Sensor back to Advanced Auto. It was $97. The Jeep dealership closest to me (Which is a bit of a drive) does not have one and will have to order one. $179.
The Advance Auto sensor reads correctly when tested with the meter.
I have not performed that test you mentioned. I will do that tonight.
I actually read that thread and forgot about that part. Funny thing is though the person with the actual problem does not clearly say where his problem located. Just that he found the problem area (wire) and fixed it.
That schematic will help me diagnose further.
Thanks. I will let you know what I find.
 
On-line, Jeep Dealership websites discount parts 30%. The last genuine JEEP CPS I bought was $82 on Amazon, shipped free, and it came from a Jeep Dealership.
 
Did the test listed at the DLC
Measured 61.2 Ohms at pins 3 & 11 with the battery disconnected and switch in off position.
Battery connected and switch in on position:
2.41 VDC at pin 3+ and pin 4- or 5-
and 2.40 VDC at pin 11+ and pins 4- and 5- respectively.
With regards to the the Crank Sensor.
I called the dealership south of me this time and it is $142. I went ahead and asked them to order it and will make the trip there tomorrow to get it. About 35 minute drive.
I am going to start probing the sensors and sensor lines now looking for a short or grounded line somewhere that would interrupt the 5 VDC signal in the sensor path.
 
I checked more sensors tonight.
Thought I made some headway when I started seeing 5V on most all of the sensors and then I started hearing a relay clicking when ever I turned the key on. I didn't hear this before. It ended up being an O2 sensor relay, as I had all of the O2 sensors unplugged. I was still getting 3 volts at what I believe is the mas air flow sensor. So I looked at that harness and general direction. The wire grouping there was hard and stiff as it rides on the intake manifold.
I cut the tape back and investigated it looked like possibly some wires were fused together. After checking them thoroughly, it does not appear that they are fused internally. The outside coatings are sticking together but metered out there is not a short.
With every sensor unplugged the gauges are still dead and the "NO BUSS" and check engine light error come on after 20 seconds of turning the key on.
I will have the OEM Crank Position Sensor tomorrow to try. Still no connection with the computer or signal to the ASD relay or fuel pump relay. I know the fuel pump relay is energized by the ASD relay so I am not concerned at this that at this point.
The manual I downloaded from Pacific Coast Manuals does not show where the signal is coming from for the ASD coil to be energized. Do you know where this signal is coming from? It does tell me it is D6 Circuit K51 18Dark Brown/Yellow wire.
 
Just guessing here. Go to where you tied your trailer harness into you jeep and inspect and disconnect it there and meter it out for voltage resistance and shorts. Also, I have read that the fuel pump ground is on the rear quarter, behind the spare tire. Check that out as well.
 
So, new developments. I had disconnected the fuel injectors and sensors along that harness grouping so that I could take a closer look at the wires that appeared to be fused together.
With all of that disconnected I had the thought, "if the ASD relay is not getting a signal to energize, why can't I just put a jumper wire to that blade of the relay to the battery and see what happens?"
So I did that and turned on the ignition key..... My gauges now work!!!:clap:
No "NO BUS" error!!! I have connection to the computer!!!! 5 errors on there but I have multiple sensors disconnected so that would easily throw those codes. I need to get the injectors and everything else connected and give it a try with my jumper wire.
I will have to find the schematic that shows me where exactly that signal wire to the ASD comes from. I believe it comes from the internal fuse panel possibly. Can someone help me trace this wire backwards from the ASD relay?
 
Good to see you are making progress. I am a decent shade tree mechanic, but not an Electrical Engineer. Wire diagrams make may head spin, and I hire neighborhood kids to fix my computer.

Have factory installed key-less entry ? If the key-less module shorts out it can cause some weird problems.
 
Yes, I have the factory installed keyless entry.
That has worked just fine during this whole process. It locks and sounds the horn and ulocks like it should. I got the OEM Crank Position Sensor today and I am going to try to see if that makes a difference. I guess I am going to have to trace back from the PDC for that ASD Relay signal wire if I cannot locate a good schematic to show me where it goes.
My guess is it probably comes from the fuse panel inside possibly.
 
I put in the OEM Crank Position Sensor last night.
Hooked up my jumper wire to the ASD relay. Cleared the codes on the computer (2 codes both O2 sensor codes) Primed the fuel pump by letting the pump run for 10 seconds. Cut it off. Let it run again for 5 seconds. (Again this is all done with the jumper wire and the key in the on position. Still do not have control with the key only) Gauges work, went to start it. Cranked for about 10 seconds and I heard/felt what sounded like a half a second of fire. The it kept cranking. Tried this again several times. A second time I got what seemed like a half a second of fire. But it never would turn over. Check engine light came on during the process.
Codes were the same O2 sensors and another code for the Cam Shaft Position Sensor?!? Now why would that be? I haven't messed with that other then to unplug it and test voltage. I still have short somewhere and I am going to concentrate on that this weekend. Finding out why my ASD is not turning on with the key. I am going to take the fuse panel out on the inside passenger kick panel and inspect.
 
Problem is SOLVED!!!!!!:clap::clap::clap::clap::clap:
I have some pics to upload but the gist of it is this.....
Even though fuses check good on the back side with your test light or meter.
Remove them all and check or replace them.
Inside the passenger side kick pannel is the fuse panel. This fuse panel in slot number 11 holds a 20 Amp Yellow Fuse for the power train control module, transmission control module, automatic shutdown relay and the fuel pump relay.
I had taken the PDC off in the engine compartment, found that slot 6 on the Automatic Shutdown Relay was the signal wire to energize that coil. This is where I knew I was not getting power. I found that wire to be Blue/with a Yellow Tracer. I followed that all the way back to the kick pannel and slot number 11!
That fuse had checked good with all the rest when testing both sides with my meter and shop light.
When I pulled it out the the tabs were dark brown! Clearly not making contact!
Replaced this fuse. Made sure previous Jumper wire was not in place. Turned key on........My guages came up!!!!! Turned key to sart. Couple of cranks and it fired right up.
Now I know I am going to catch a lot of flack for not pulling the fuses. But I was chasing sensor after sensor till I realized that my Automatic Shutdown Relay was not energizing. It was only until I started diagnosing this issue that lead me to this fuse.
So, for futer refference, if you have a "No Buss" error and no guages, and if your fuel pump is not running with the switch on. Your ASD relay may not be energizing. It is a simple check by pulling that relay and checking the slot cosest to the firewall. It should have 12V with the key on. If it doesn't, you are not going to start your engine!!!
I will post picks soon for reference.
Thanks to those who helped me. I hope this helps someone else out there who is suffering the dreaded "NO BUSS" No Start issue.
I now have a new OEM Crank Position Sensor, most all of my contacts have been cleaned and dielectric greased. All of my grounds are cleaned and making good contact.
I did break a pcv plastic line while working on the electronics under the hood but other then that no real casualties to speak of.
 
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