Hey everyone! I have a 2002 Dodge CTD auto with 277k. I’m getting the “no bus” message on my odometer screen with codes 900 920 921 940 950 and 999 on the self check. The CEL, ABS, low fuel and air bag lights are on. I’ve cleaned up the connections at the PCM and fuse block, cleaned grounds and still no fix. The truck does start and drive normal so I don’t believe it’s the PCM. Any input is welcome thanks! 

Edited August 11, 20195 yr by Beam52

I will take stab at it. I think the 900 codes are all instrument cluster codes but not sure. If so your cluster maybe bad or you justmight need to pull it and clean up the contacts on the two connectors. It is easy to pull the bezel and the cluster to get at them.

Well went to O’Reillys and they pulled up high voltage to the coolant temp sensor, over-boosting and no DTC detected. I don’t believe any of these would cause a no bus would they? 

How did they pull up high voltage to the ect and map over boost with no dtc detected? Both of those are dtc's and should display a code #. 

 

I have been dealing with a high volt code on mine for the past 2 weeks. 118 ECT high volt. Have not had time to work on it but the other day I got wild hair and disconnected my exaust brake connection to the ECT and the problem is gone. I have problem in the e brake wiring. 

 

That being said the problem could be deeper but that easy to fix. Others smarter than me will be along to help. But it cant hurt to pull the cluster and clean the connections. Could be ground issue also. Just not sure where to start on that.

All he did was hook up and gave me those three things from the Bosch scan tool lol so I’m gonna replace the temp sensor and maybe get a boost fooler, maybe clean the map sensor too. But definitely going to clean the cluster connections and if anything I’ll get one for $300 included exact mileage reset. But thanks for trying! At least someone tried. 

Others will be along. Kind of slow on the weekends sometimes. It is probably not your sensor but that o e is cheap enough to try. I have a couple spares. And unless you have some mods that would require a boost fooler you do to spend the money on one, just find the problem. Could be the sensor, but they a re pricey just to throw at the problem. The same could be said for the boost fooler. Tell us more about your truck. You can go to your profile and add a signature that will show up on every post like the one on mine. 

When I had a no bus a couple years ago, it was my intake grid relays, would've never guessed that, I took it somewhere because I have no electrical experience.  I was fortunate that they found it pretty quickly, otherwise it would be expensive to have them look for something for hours and find nothing.. 

I was wondering if something such as my bully dig tuner or like Alexio mentioned the intake grid relay would short it out causing the no bus, I’ll have to take the positive cable off and see what happens. Same with the tuner 

Someone else had some wierd issue that was caused by his grid heater relays. @Evan I believe.

PCM is what starts the CCD Network. The cluster is what provides the bus bias voltage for the rest. 

 

ECM can run as a standalone and run the engine but can't get any data from or send it to the PCM. Should have 2.49 and 2.51 volts on the CCD Network lines after everything booted up and at rest.

 



When I had the “no bus” message my testing led to bad pcm, so sent it to ACS and tested good but they had a difficult time getting a good connection with it. So that seemed to be my problem. I cleaned connectors again and plugged and unplugged many times and everything worked. ACS suggested to not use dielectric grease. 

Hope this is helpful. 

Is it a give away that the PCM or ECM  is good given that the truck runs and drives like normal? 

ECM only. Truck only needs a ECM to run.

 

PCM can fail or be missing and still start and run (drive).

Ok so I hooked up a friends scanner to it today. It reads it has 9.75 volts to the ECM, but has a DTC saying it has a communication error with the ECU. Bad PCM?  

Also have a P1698 code

 

Disregard the P1693. It's just a flag pointing there there is other error codes could be in either module. Now follow the diagnostic on the PCM.

 

Well got a new Pcm installed, still no bus. Back to the diagnosing. 

New or reman PCM? 

Reman for $650 and 2 year warranty 

Good deal. I had to do the same when the alternator shorted out the PCM it burned the circuit board bad. Yeah the price on the reman PCM it pretty steep but its a complete unit all programmed and ready to go. Make sure to fix the problem before installing the new unit.

Well I installed it thinking it was the fix and still have the no bus and no cluster. Also have a new used cluster and that wasn’t the fix either. I don’t believe it’s the ecm because the truck still runs and drives and has a voltage reading on the code scanner. I also have just over 1 year old  batteries and a newer alternator. 

Edited August 24, 20195 yr by Beam52

Go back over the CCD network wiring. Check for the 2.49 and the 2.51 volts on the bus.