Different Kind of No BUS

Hey all. I am having trouble with my 2006 Liberty. I have looked all over for answers but can't find anything that fits my scenario and everything that I have tried from other threads has not worked.

2006 Jeep Liberty Sport 3.7L Automatic.

Crank but no start scenario. It died while driving and would not restart. Cranked as normal but wouldn't even cough while cranking. I messed around with it for about a month and could never get any kind of life out of the engine. I replaced the crank sensor and the cam sensor, neither one fixed it. The scan tool is able to connect to the computer and read codes but when the scanner is connected to the vehicle no bus comes up on the odometer. The jeep shows no codes unless i unplug a sensor here or there and try to crank it. The code then shows up, can be read fine, and is able to be cleared with no issues.

I did find that I am only able to read 0.01V on the 5V reference circuit with a volt meter. As a test I applied 5V across the reference circuit at the throttle position sensor with a 5v supply connected to the battery. The Jeep cranked about 6 revolutions and fired right up. I let it run for about 45 minutes with that supply voltage on the TPS connector and went to shut it off and disconnected the supply voltage first. The Jeep did not die when the supply voltage was removed which greatly surprised me. After that it started and ran, and even drove fine, for about 6 hours. Even was able to shut it off and restart it numerous times.

I shut it off after driving it a couple miles and it sat for about 30 minutes before I went to restart it. It would not start again. I hooked the supply voltage back up to the TPS connector and it started right up. That was last night. It has sat for approximately 12 hours now but I just went to see what it would do and it started just fine on it's own twice back to back without the supply voltage applied to the TPS.

Does anyone have any ideas on this? I have never seen a vehicle of any sort act like this and, to me at least, it seems so much different than any of the other crank/no start and no bus scenarios I have found elsewhere.

Thank you in advance for any help that you may be able to give me. If there is any other information needed that I have not provided just let me know and I will try to provide it for you.

Did the instrument cluster work during this failure? There is a few different scenarios but I can throw a few things for you to check. If the cluster is not working but giving you a No Buss it can be the electrical plug connections on the back of the cluster. Remove cluster and clean with electrical cleaner (CRC) be mindful not to spray the board, just inside the connectors.
I think you can rule out a PCM because you can read codes set by you unplugging sensors.
If the TPS is acting up then it would cause a no start situation. Applying the 5v to the reference circuit of the TPS caused it to run for a while then I would start with testing the TPS.

Do you get the red LED on the left of the cluster for the SKIS anti theft system either flashing constantly or staying lit when ignition is ON?
This Led should light up for a few seconds then go out if SKIS is OK.

Try swapping over the ASD relay with an identical one nearby.

Otherwise could be a wiring problem. First re-plug the connectors on the PCM a few times with battery disconnected...may be a dirty contact there.

You need to start tracing the missing +5 volts...if you do not have the wiring diagrams download the 2006 Jeep KJ Service Manuals here here..section 8W has the wiring diagrams.

Jeep KJ Manuals: Index of /manuals/Jeep/KJ

KJownerX2 said:

Did the instrument cluster work during this failure? There is a few different scenarios but I can throw a few things for you to check. If the cluster is not working but giving you a No Buss it can be the electrical plug connections on the back of the cluster. Remove cluster and clean with electrical cleaner (CRC) be mindful not to spray the board, just inside the connectors.
I think you can rule out a PCM because you can read codes set by you unplugging sensors.
If the TPS is acting up then it would cause a no start situation. Applying the 5v to the reference circuit of the TPS caused it to run for a while then I would start with testing the TPS.

Click to expand...

The cluster has worked the entire time. I have, twice, months before this happened, seen the cluster appear to go through the post while I was driving but I had basically ruled out the cluster issue since the whole time this has been going on it has not given me any problems. The strangest thing to me about the no bus issue is that it only comes up no bus when the code reader is hooked up to the obd port under the steering column instead of being a constant no bus on the odometer.

Billwill said:

Do you get the red LED on the left of the cluster for the SKIS anti theft system either flashing constantly or staying lit when ignition is ON?
This Led should light up for a few seconds then go out if SKIS is OK.

Try swapping over the ASD relay with an identical one nearby.

Otherwise could be a wiring problem. First re-plug the connectors on the PCM a few times with battery disconnected...may be a dirty contact there.

You need to start tracing the missing +5 volts...if you do not have the wiring diagrams download the 2006 Jeep KJ Service Manuals here here..section 8W has the wiring diagrams.

Jeep KJ Manuals: Index of /manuals/Jeep/KJ

Click to expand...

I haven't noticed the light flashing or staying on. Even when it does a no-start it appears to do a normal post and nothing looks off as far as anything i see on the cluster.

I know one of the first things I tried was swapping around relays to check to see if I had a bad one. I know I did the fuel pump and a couple others. I will try the ASD to make sure. I am really starting to think it's a loose connection or a break that is getting intermittent connection/jumping to ground. I have checked all the ground wires that I can find and they all seem good. Loosened, cleaned, reseated. I have even tried making temporary extra grounds to verify that it was not a bad ground causing it. I am really baffled about it now as I have been able to start it and drive it without any issues at all now for the last 2 1/2 days. I have been keeping the power supply and wires with me to "restart" the 5V reference circuit again if I had problems but I had to have the 4x4 of the jeep with the weather that just came through. I am just scared that one of these times the power supply trick wont work.

I downloaded the repair manual you mentioned and I'm going to start going through trying to find a bad wire. Would it work to check for continuity between the 5v supply wire/ground and the 5v return wire/ground at each sensor to check for a short to ground? Tracing wiring systems is something I have no experience at.

Also, sorry for the dual reply, I couldn't figure out how to do quotes from two different comments and reply to both at the same time.

Ok I presume you have a digital voltmeter.

Find the wiring page in section 8W that shows the wiring going onto your throttle pedal which should have +5 volts on it. Trace this wire all the way to its source...probably the PCM...the wire color for this circuit will stay the same no matter how many times it branches off via splices.

I will look at the wiring diagram but you basically are expecting to see +5 volts on a pin at the PCM and all the way to the end point where it seems to be missing.

I have not worked on the 3.7 gassers but I know on the CRDs the wiring harness goes all around the engine bay like the Beltway around Washington DC....a start point such as the fuse box and an end point such as a PCM pinout may physically be about 8 inches apart but it usually goes about 8 feet...with a lot of connectors along the way!

So you may have a broken wire or a bad connector connection somewhere.
Best way to check wiring is to strap a small sharp pin or sewing needle to the Red lead probe of your meter and piece the insulation on the wiring to touch the copper inside.

Then with the Black lead of your meter on ground you will see the presence or absence of your wayward voltage without disturbing the connectors....close up the small holes in the insulation with glue or melting with a soldering iron when you are finished.

You could also have something pulling the voltage down such as a short to chassis/ground. This can be difficult to find as you have to isolate all paths that this wire goes to via its splices.

I will have a look at the correct logic page in the meantime.

OK I have had a brief look at section 8W of the 2006 Jeep KJ Service manual....there are changes...and mistakes..between the years and the colors of the wires change as well.

Page 8W-30-23 shows the accelerator Pedal Position Sensor with pin 6 having a Brown/Violet wire ie. Brown with a Violet stripe at that position. This wire goes through connector C100 via pin 46 and then connector C111 pin 9..the index of section 8W gives the location of the connectors. Then hits the PCM at connector C2 pin 24 which is the 5 volts that you are probably interested in.

So these connector pins may be dirty or the wire is broken...fortunately no Splices are shown!

So measure from the source to the destination to see if there is +5 volts at the source which then is supposed to be at the final destination!

Have fun....may be a lot more complicated than the above!

Thank you for your very detailed response. I apologize for how long it took me to get back to the forum. The wife has been in and out of the hospital the last week and a half and had to have surgery Friday. I will check all of this out as soon as I get the chance to once things get somewhat back to normal. In the meantime I really appreciate everyone’s help in this matter.

Hey guys, I am sorry it's been so long since I have replied to this thread. I started getting all kinds of codes and they changed sometimes. I was starting to fear that the computer had crapped out on me because of the way they were coming and going. I had gotten codes for the throttle position sensor, the camshaft sensor, the crank sensor, as well as the knock sensor. I had previously replaced the cks and the cps. I went ahead and threw a new fuel pump in because the fuel pressure was erratic and it helped some but didn't fix everything. After the fuel pump replacement all codes went away except for the camshaft position sensor and a code for battery loss (I'm assuming from when I disconnected the battery to replace the fuel pump). I got a warranty part for the cps and put it in, cleared all codes, and now everything seems to be working as it should.

I want to thank you guys again for all the help. Hopefully the problems are gone for good now and maybe this could help someone else in the future.

The only thing I'm confused about is why the 5v reference circuit was showing dead on all sensors. Can a bad cps really take out the whole circuit like that? I'm sure the no bus issue was being caused by the reference circuit voltage being nill and it is not coming up anymore.

maybe there was a short in the CPS that caused the whole 5V to go down.