I have a 99 dodge 2500 with the 24 valve cummins. I keep getting the no bus message on the instrument panel. I have cleaned all grounds and looked for lose wires. None of the gauges are working. Im thinking the pcm is bad. Is there any way to test the pcm. Where can i buy one at a decet price?

 

Could be the PCM or a bad sensor on the 5V reference wire. Buying one u can't help with never had to

 

What is the 5v wire?

 

The 5V wire runs too numerous sensors. It's the PCM "feel" wire. It sends 5V the sensor modifies the voltage sends it back to the PCM, so the PCM knows what the sensor is doing. The problem is every sensor uses the same wire. So if the sensor goes bad "short to ground" then you'll get the NO BUS in the odometer

 

Can anyone tell me if a PCM out of a 2 wheel drive truck would work in my 4x4?

 

As long as it's a 99 yeah just some lights won't work (4wd) and the abs and brake lights will be on until you flash your VIN

 

I guess i need to take it to a dealer to have it flashed?

 

An independent shop with a GOOD scanner may be able to do it, and cheaper..... Also, it depends on where you get your PCM from. Local parts stores can get 'em, and already flashed to your vin.... and if there is a problem with it, the store isn't gonna go anywhere, and you get to talk face to face with a real human. (hopefully....)

But, do you really NEED a PCM???? Try unplugging the various sensors on the 5 volt bus. See if the dash comes back to life. Last sensor you unplug is likely the culprit. O2 sensors, especially the rear sensor, are notorious for this kind of thing.

If you don't have a service manual for your truck, download one from here. Wiring diagrams are in section 8W. Should be able to determine which sensors are on the bus.

 

Thanks man. I will definently try that. As i dont want to spend alot of money on a pcm that may or may not be the problem. Im new to the dodges. Always been a ford fan. But this truck has all the options i want and the price was right.

 

Before you go whole hog on spending money hook up a obd II scan tool with live data and see if the sensors read anything useful. On a diesel you should be able to get at least RPM, temperature and oil pressure.
The CCD bus uses differential signaling so forget about grounds for now. There's a lot of good info here : https://mopar1973man.com/cummins/art...data-bus-r329/

Do you have access to/know somebody with a shop level scan tool ? The tool can access the CCD bus directly and it might help figuring out if the whole bus is dead or maybe just a connection. In lieu of that you'd probably have to check all the CCD wiring shown in the link above.