Had my 02 Dakota 4.7 4wd and 105k miles for about 6 months now and it quit on me the other day. Getting no bus error. At first it quit on me after a short drive and I parked it and tried starting it about an hour later and it won't start with no bus message. Now it quits even idling for about 10 min. I saw the old post here explaining the 5 volt reference circuit which is what shutting the truck down when PCM is failing and not supplying the 5V to the various sensors. However I've tested mine the same way and even after triggering the no bus condition I am getting 5V coming out of orange wire from PCM. And also confirming getting 5V on TPS and MAP sensors with no bus conditions. Can anyone point me in the right direction for further testing? Thanks in advance. Oh after I took TPS sensor out and put it back in I'm getting the p0123 error for high voltage, don't know if that could be relevant.

 

Any sensor on the five volt bus can take down the entire system. Finding which one is the issue is the fun part..... Can try disconnecting sensors one at a time, see if the no bus error goes away, and the engine will run for longer than 10 minutes. Of course, that won't work for cam or crank sensors.... PCM needs those to start/run the engine.

 

So I was going to to go test the crank and cam sensors but since they're fairly cheap and I can get them at local autozone would it make sense to just replace them while I'm at it and eliminate them out of the equation?

 

Unfortunately, no. The aftermarket sensor suck, quite honestly. And very few folks have any success with them. For critical sensors, (and those two are at the top of the list) you want genuine mopar sensors. Cam sensor is only used at startup, theoretically.... so, if it starts, likely not that one.

 

Is there any test I could perform with a multimeter to narrow it down to PCM vs sensors? If PCM still sending 5V to the sensors even with no bus condition does that tell us that PCM is likely fine?

 

It's a crap shoot. Doing the unplug one at a time thing works fairly well. Need some pretty specialized tools to accurately test the crank/cam sensors though. I would first check for any stored or pending codes though..... so what the PCM thinks is going on, if anything...

 

So I just went and did more testing. I'm getting 5v on every one of the sensors map, TPS, crank and cam. Checked the ground wire on each connector too to make sure they're good. I pulled an ignition coil plug and I get battery voltage as soon as I turn the key and during cranking but get nothing with no bus error. So it's cutting power to my ignition coils which is why it won't start. I ordered a used PCM off eBay, would it at least be able to run the truck without flashing my VIN or do I have to flash it for it to even work?
Oh and there are no stored or pending codes I've tried scanning multiple times.

 

Used PCM *should* run the engine without being flashed, some systems will whine about the vin mismatch.... usually just ABS, and SRS. Give it a shot, see what happens.

 

Got it today and the truck starts but cuts right out within a second like some type of security feature it seems. Are there knows scanner brands that I could flash my VIN on this PCM with?

 

Is the security light in the dash flashing? What color is your key?