"No bus" error message on the cluster.
#1
"No bus" error message on the cluster.
2002 Ram Van (5.9).
Today, I got the dreaded "no bus" code.
The scanner can't communicate with the PCM, and the self-diagnostic procedure revealed the 920, 921, & 999 code (these are PROPRIETARY codes, NOT OBD2 codes).
This failure was completely spontaneous and occurred at start-up.
Before I spend all sorts of money on a new PCM, how can I *definitively* tell if it's causing this? If there is a wire to the PCM that has 5 V going to it (as I've been told), which pin is it, what color is the wire (or wires), and which connector has them?
Today, I got the dreaded "no bus" code.
The scanner can't communicate with the PCM, and the self-diagnostic procedure revealed the 920, 921, & 999 code (these are PROPRIETARY codes, NOT OBD2 codes).
This failure was completely spontaneous and occurred at start-up.
Before I spend all sorts of money on a new PCM, how can I *definitively* tell if it's causing this? If there is a wire to the PCM that has 5 V going to it (as I've been told), which pin is it, what color is the wire (or wires), and which connector has them?
#2
Actually, there are a couple wires coming OUT of the PCM for the 5 volt feed to the sensors. A short in any one of those circuits can cause the no bus error. Rear O2 sensors are a common culprit. Easy to test though... Verify you are still getting the no bus error, then turn off the ignition, unplug the rear O2 sensor, (if you have more than one, just do one at a time) turn the ignition back on, see if you still have the error. Repeat that process for every sensor on the 5 volt bus.
#3
#5
Actually, there are a couple wires coming OUT of the PCM for the 5 volt feed to the sensors. A short in any one of those circuits can cause the no bus error. Rear O2 sensors are a common culprit. Easy to test though... Verify you are still getting the no bus error, then turn off the ignition, unplug the rear O2 sensor, (if you have more than one, just do one at a time) turn the ignition back on, see if you still have the error. Repeat that process for every sensor on the 5 volt bus.
Can you tell me what sensors are on the 5 volt bus besides the O2 sensors? Once I know what's included, I can start unplugging things one at a time to see if the error message disappears.
Last edited by Celticwarlock; 05-10-2024 at 12:50 PM.
#6
#7
So far, the transmission range switch (PRND21) and both oxygen sensors were disconnected, but there was no change.
Would the change be immediate, or would "no bus" disappear only after some kind of re-set?
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