2002 dodge ram 3500 no bus displayed

Greetings I'm from new York . 2002 dodge ram 3500 van. Vehicle will start run and shortly after cut off. Sometimes will start right back up, other times it will crank with no start. The odometer displays no bus. No codes present. Back probed pcm bus negative and positive. Did not receive signal I figure I should see. That points to bad pcm or what? The voltages on the waveform did not vary by 2 volts. I may be able to post the waveform if I can figure out how to get it off the scanner. Any help would be appreciated. Thanks in advance

Hello betterway357,


The first thing you need to check for is a 5v Ref at one of the vehicles sensors, like the TPS. If you don't have a 5V ref then you should start by unplugging other sensors that use a 5V reference, Most notably the crank sensor.

And there are sensors that use a 5v reference inside the transmission.

If the 5V reference returns after unplugging a sensor then that sensor is your problem

Thank you for the reply. There was a 5v ref signal present at a sensor. What would this 5v ref have to do with the bus signal? Then even if a sensor was pulling the 5v ref down shouldn't a code be thrown whether directly related or indirectly? I will post the waveform. I appreciate the help ro-longo

If you have the no bus message you shouldn't have communication with the pcm. Moving on if you have 5v ref then your computer is atleast partly powered up check your asd relay and see if it's being energized the pcm sends the relay control power for 2 seconds with koeo and then all time during crank and run. There is also a feedback from the load side of the relay to the pcm . If it doesn't send the signal or if the relay doesn't work and it doesn't get the feedback it won't start .... I personally think it's a terrible design but that's dodge for you... if you need diagrams they can be found at Bbb industries or someone can post them for you . You will need to confirm power and ground at pcm as well

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I would want to know what is missing when it doesn't start, such as spark,injector pulse, etc. I would get direction from there, maybe focusing on the asd relay output - the green/orange wire that powers the coil and injectors. If rpm signal is lost, there will be no asd output. You have the 5v ref., so the ecm is somewhat alive. I'm pretty sure a crank sensor and/or cam sensor issue will take down the bus.

Thank you for the help? Have you looked at the waveform? I will check the asd relay. For proper operation. Also I will check what's missing once I get the no bus display. To me it looks like a resistor is faulty on the bus from the waveform but I'm no expert. I really do appreciate the time taken out for a reply john z and Ben

I'm not an expert on that bus either, but the times I have seen the bus down the cluster was also dead, and there was no communication on the scan tool. Knowing my limitations there, I would focus on whether the pcm is really the cause of the no start, or is it something else taking it down.