Have a 2002 5.9 RT that ran great up until this morning. went to start and all it did was crank over, all electronics work except the gauges. Pulled a code of "no bus". The only thing that I can remember that might be related is a couple days ago the Temp, MPG and Avg MPG display was just showing dash lines (-- --). I have checked the 3 plugs at the PCM and cleaned them, I did notice that on the middle plug the installation on the brown wire was missing about an inch down from the plug, check continuity through the first 4 inches and still good. Had about 2.6 volts with the key in the run position. I also went through the steps to reset the PCM, still no start. Is there anything else I should be looking at or am just going to have to face it and replace the PCM? Thanks,

 

If you are getting a no bus code and all the plugs are connected tight than it looks like you need a new PCM.

 

Just to make sure I am tracking right, the PCM is located on the right side (passenger) fender engine compartment, and is sometime called a ECM by part stores, 3 plugs, is this correct?

 

Yes, thats the one.

 

Just want to make sure I need a PCM, dont want to spend the money if I dont need too, but is it common to have a PCM just go bad without any kind of warning, ie. other codes or engine running rough? Thanks for the help, since I might need a new one any good advice on where to buy on, was looking at "All Computer Resources INC" on line, any ideas. Again thanks for the support.

 

the 'no bus' error code in the odometer window means that the PCM is not communicating with the with the cluster, it could be a bad PCM, it could be a bad connection somewhere, it could be a shorted sensor taking the bus down (i believe its the cam sensor) if you unplug the offending sensor you should get the odometer display back. when you turn the key on.

however there is no way for us to say with 100% certainty that you need a new PCM, it is the most likely cause of a 'no bus' code, but not the only.

 

Well, I took the PCM off 2 days ago to get a new one, which I am still waiting for, and yesterday I disconnected the + and - cables, hooked up the old PCM and reconnected my battery, fired right up. Drove it around for about 3 miles last night, got in it this morning fired right up again, drove it 4 miles, turned it off, let for about 1 1/2 hours and would not crank, had "no bus" again. disconnected the + and - cables and the 3 plugs on the PCM, let it sit for about 20 min reconnected everything fired right up, drove it about 100 yards and it stalled but fired right up and drove it home with no issues. Have not tried to restart yet was going to wait till morning. Any idea of why, think I might need that new PCM?

 

Try it again and if after sitting for a short time it won't start again put a bag of ice on the pcm without disconnecting anything, if it fires up the pcm is overheating it needs to be replaced.

 

Finally a subject that I actually know something about.Most the time, Im asking the questions. =) With the "no-bus" in the odometer reader you absolutley will need a new PCM, its a pain because your going to have to order one, wait for it to be programmed and sent to you. Good news is that replacing the PCM is actually very simple, I did my own. If you disconnect the wires and it works for a bit and then just doesnt, it is because you are basically "reseting" the computer...for lack of a better term. However, while doing this may get you a few miles, it is not going to be the fix. There are many websites that have the PCM as well as most of your local auto stores. Good luck! At least its only a couple of bolts and a few plugs, then you are good to go.

 

an intermittent problem like this is usually a connection problem between the PCM and the dashboard.

this means that you may or may NOT need a new PCM, if the bad connection is internal to the PCM a replacement will solve the problem, if it is not then a replacement will not solve it.