"No bus" what is wrong and how can I fix it?

Hey Doug,
Essentially "No Bus" means somewhere communication w/ the various modules (computers) was lost. This could be a controller actually causing this or an intermittent short or open along the bus wiring. Its a very hard problem to diagnose and can be labor intensive, unless the problem occurs when a tech is looking at it!

Chris

I hope you can help me. My truck is getting hot and shutting down. No power, No stering, and No breaks. The reading on the dash reads (NO BUS) wants it cools down it will restart. please help. Thank You..

No Bus indicates there is a breakdown of communication between the power control module and its accessories (which are many). Is the vehicle actually overheating or does it just shut down?

Let me know.

Joe

The truck is just shutting down when it gets hot..Joe

If it isn't overheating but shuts down when it warms up check the wiring harness to the PCM. Make sure it is tight and there is no corrosion. Agani, the no bus indicates there is a break down in communication between the computer and components.

Computer problem
2000 Dodge Ram V8 Two Wheel Drive Automatic 69000. miles

got my oil changed and tires rotated, next day the NO BUS light came on,ABS light &,gas light,(when i know i have half a tank) and airbag light & gauges dont work on 2000 dodge ram 1500

The no bus indicates there isn't a connection between the computer and its components. Check the wiring harness under the hood to make sure it is tight and no one bumped it while they were working.

Also, will the van start and run?

Let me know what you find.

Joe

in the mileage window it says no bus and when it will start and drive then it quits the gages go all the way down then something clicks and it will start again then shuts down again

The no bus indicates there is a break down in communication between the computer and its components

I have a 1999 dodge ram 1500 5.2 L/base model/automatic. I went to start my truck one day 3 weeks ago and it would not start/crank, since then I have replaced the pcm module, a variety of different fuses, and I just replaced the crank shaft position sensor and the dang truck still will not start. Do anyone have any knowledge as to what may be the issue? I have already spent a lot of money replacing the things I already mention. I have also tried unplugging all the fuses and testing them with a multi meter. Please at this point I'm begging for help to fix it myself versus taking it to a shop. Also when I try to start the truck the "no bus" comes on after a few minutes when I unplug the battery and re connect it. What am I not checking?

The most common cause is a bad ECM. They break down inside and basically can no longer transmit information needed to run the vehicle. Also, they have been known to throw incorrect codes when they fail.

I purchased a new ECM plug it up and my vehicle still shows no BUS and all the little ABS brakes and dash lights are on, gauges not working.

Hello, I'm Danny.

Quick question first. After installation did you you use or have a factory Dodge DRM scan tool used to initiate the module? Otherwise truck with have a code or no start. I've attached a picture below.Hope this helps and thanks for using 2CarPros.
Danny-

Engine was running fine. Shut it off. Tried to start later. Won't start and have a "no bus" on cluster. Have no spark, fuel pump only works when jumped, ASD relay has been checked OK. bus+ & bus- both have 2.5vdc.

The no bus code indicated the computer has lost signal. Check the wiring harness to the PCM to make sure there is no corrosiion and it is tight. If it looks good, have the PCM tested.

Found grounded wire on Crank Position Sensor. Installed new sensor. Truck starts and runs fine.

Excellent job! Glad you found it. Let us know if you have questions in the future.

I need to know where the different modules are to try to correct a NO BUS issue.

Good afternoon,

I attached locations of the PCM, TIPM, TCM and the ABS module for you.

Roy

thank you. Is there any other modules that I can unplug to try to figure out which is causing me all this grief?

The instrument cluster is a module but if it was an issue, you would have functions in the cluster that would not work.

Start with the ones I listed.

Roy

Okay, I will let you know what happens.

Sounds good.

Roy

Hi Roy, checked the ones that you suggested all okay. did self check on dash and it okay. Still have no bu5 showing, no gauges on dash, no brake lights or signal lights. when I check with scanner I can get a tachometer and speedometer but not a good way to drive. Am thinking broken wire but where?

Okay, no BUS possibilities are below and I attached a flow chart for you as well.

Roy

SYMPTOM
BUS (+/-) SIGNALS OPEN OR NO RESPONSE FROM INSTRUMENT CLUSTER

POSSIBLE CAUSES
- Attempt to communicate with another module
- Open ground circuit(s)
- Open fused ignition switch output circuits
- Open fused B+ circuit(s)
- Open PCI bus circuit
- Instrument cluster

Hi Roy, I am unsure if the program that I have can do that. The 2 programs that I have are OBD Doctor and OBD Wiz. I am just learning how to use them as it has been over 35 years since I worked on vehicles so I guess I am very old school, not real confident in working on these new vehicles but am learning. Will let you know what I find.

Hi Roy, I just got a reader (CR 319 by Launch) and it shows P1698 transmission module. This is when key is in on position. Do I need to have engine running and check again?

Okay, you got communication.

The possibilities are below. I would suspect the transmission control module is causing this issue.

Roy

P1698
Descriptor
No Bus Message From TCM
Probable Causes
No BUS Message from Transmission
Powertrain Control Module (PCM) Programmable Communication Interface (PCI) BUS Circuit Open
Wiring Harness Intermittent Problem

So can I replace the TCM with one from another truck or is it something that I have to go to a dealership?

It would need to be flashed to your VIN. The dealer is not the answer. They are way over priced. Look around for a private shop. They can do this as long as they have the proper scan tool for about half of what the dealer will charge you.

Roy

Hi Roy, I have checked around and no one seems to be able to help me. I guess I either I buy a programmer(need to know which one) or go to dealership. I have a used transmission module and a brain module so I guess I could take both and have them flashed to my VIN and then see what happens. I still think it is a broken wire but I am not sure where to start. Just so frustrated with this right now and just got phone call that my dad is in hospital needing surgery. Will update on what I find in tracing wiring.

Keep me updated.

Roy

Hi, went to work the other day and, as I'm driving my transmission cooler warning came on. This happened just after I started out. Suddenly, all my gauges stop working and on my odometer it says "nobus". And all my warning lights came on. Engines is still running fine. Just as suddenly it all goes back to normal. What are the possibilities? I have 140,000 miles on the truck and it's been running great. I did have the transmission overhauled about 1 1/2 years ago. But that's it. Thanks

Hi,

This "No Bus" warning is indicating an electrical issue. More than likely this is a connector that has corrosion in it or a wire that is rubbed through.

Unfortunately, there is no way to tell you where this could be coming from. The way your modules communicate is over what is called a communication bus network. Basically, the modules send coded voltage signals to each other to send the messages that they need to in order to communicate properly.

The way to diagnose this is to monitor this bus voltage while it is acting up and then you can track down the issue by systematically disconnecting portions of the wiring until you find the issue.

This is the most complicated type of wiring/electrical diagnosis and causes many of the most seasoned techs major headaches at times.

What I would suggest, is monitoring when this happens, in turns, what speed are you going, did you run over some bumps? Just start tracking what it takes to get this to happen so that it can be replicated so that the chances of finding it will go up. You don't need to worry about any damage to components like the transmission. This is simply a wiring/electrical issue and will not do damage to the actual components.

There is a small chance that a module itself is the issue however, it is most always a wiring/connector issue.

Hi all, I pulled fuse #23 and everything except remote start, door locks and several other things until not working but then alternator went out. so now I need to replace alt and battery. Still thinking broken wire but now I am also thinking remote starter module may be the culprit.