2002 Dodge Durango, 4.7, No start, No bus message

And no error codes, stored or pending. I do have 5 volts on the PCI bus circuit, but can't seem to be able to communicate with the PCM. Disconnected all of the major sensors one by one anyway to no avail. Also disconnected all major components connected to the PCI bus one by one to no avail either. Need help on where to go from here. Do not have a lab scope. Just a code reader and multi meter. Any suggestions would be greatly appreciated. Thanks in advance.

Hey there, welcome to the forums!

Just so I'm clear, where exactly did you measure 5V on the PCI bus circuit? At the DLC? Just trying to get an idea about where you've done your testing so far.

I see that you've disconnected sensors, good move. Looking for a short, right? Even though disconnecting them didn't help, I'd still suggest checking the 5V reference circuit, just to make sure it's there. Given the no start and no communication, I'm gonna wager that it's gonna be MIA.

With the testing you've done so far, I think my next move would be to check powers and grounds at the PCM itself. Your multi meter will work perfectly for this, no scope required. It'd also be super easy to check fuses before digging the computer out. Be sure to check both fuse boxes, under the hood and under the dash.

Let us know how the 5V reference and fuse checks turn out, and we can go from there!

I tested for the 5 volts on both the MAP and TPS connectors when they were disconnected.
I had read various posts from other owners about shorted sensors. And they suggested unplugging each one by one. Power cycle the key to see if the No Bus message went away. Ran into another post about the various components on the PCI bus causing the same problem. So I unplugged each of those one by one too.
By using the RPM gauge on my code reader, I'm not getting any RPM indication while cranking. So I agree. Either the PCI bus is completely down, or the PCM is fried.
I'm sorry. I neglected to mention that I do have 12 volts on pins 2 and 22 at the black PCM connector. Pins 31 and 32 both appear to be good grounds. I have disconnected and cleaned every body ground that I've found so far. Even made a few of my own temporary grounds just using alligator clips directly to the battery.

Just some thoughts here myself. Have you verified on this cranking no start that you have no spark or no fuel pressure? What is odd here is you are saying you can communicate with your scan tool and you see no rpm reading while canking. When your checking your powers and grounds the computer are you checking the circuits with everything plugged in and cranking the engine over while watching your meter? If not I would redo your test and watch your meter and see if your scan tool dies while cranking. Do these tests again and tell us what you find. Also make sure you have your negative meter lead on the negative battery terminal while dong these tests. Also could someone post a schematic of this Pci Bus system? I don't have one but if someone could post it I might be able to help with this. I have quite a bit of experience working with no Comm issues on Buses. This might be a little different, but the concepts still apply here.

I do not have spark or fuel pressure.
Last I checked, I could not communicate with the PCM through my scanner. And everything was plugged in. My meter did not die, just showed 0 RPM while cranking.
I do not have a back probe. So when I was testing for power and ground at the PCM, the black connector was unplugged. All of the other sensors and components were plugged in.
Thanks again for your help.

You need to have it plugged in to do a accurate test. Go to a hobby store or a sewing place and pick up some T pins. Use those to backprobe into the powers and grounds and do your test again. The way you did the test was wrong. Your meter has high resistance in it. So the meter could lie to you because you have very little current flow in the circuit due to the meter. Everything has to be plugged in and current flowing to get a accurate Volt Drop measurement. Then the meter can actually see the potential difference in the cirucit. Redo your tests and let us know what you find.

Thanks for getting back to us, sir!

So I totally struck out on the 5V reference circuit, was totally expecting you to find none. Oops!

It's awesome that you've already done PCM power/ground checks, those were the exact pins that I was going to suggest testing on. busjockey is right, though, voltage drop testing with backprobes is the best way to be certain in these cases. Either that, or substitute a load for those wires using a tail light bulb.

5V ref is there, powers and grounds looking good, doesn't bode well for the PCM! Poking around on the BBB Industries site, I actually found a different power/ground diagram with some additional pins. Take this with a grain of salt, as I'm not positive that this is the correct diagram. Just don't want to miss anything before calling a module.



Thought about a Chrysler 8V CKP/CMP/VSS circuit, but the diagram says these hall effects use the 5V reference instead. Still, might be worth checking either the cam or the crank sensor for a reference voltage. Finding zero would suggest that there IS a separate reference circuit.

Sorry guys. Been on the road the last couple of days. This is the soonest that I could get back. Current battery voltage going directly from positive to negative on the batter is 12.18. The only anomaly that I've seen. When the PCM is unplugged, I get full battery voltage (12.18) on pins 2 & 22. When the PCM is plugged in, #22 drops to 12.14. Which I'm thinking is normal since it's powering up the PCM. Pins 31 and 32 both appear to be good grounds. I've tested them between one another and also directly to the battery, and get the same voltage readings.

By back probing the MAP connector with everything plugged in. I've got 4.47 volts between pins 1 & 2. 5.17 between 1 & 3. and .72 between 2 & 3.

No worries about getting back to us, sir!

I agree, the voltage drop you're seeing on pin #22 seems to indicate some kind of load on that circuit when plugged in, good stuff. The grounds are looking good, too.

I've never measured a 5V reference sensor that way that you did, between pins on the connector, but I think that all sounds right. Showing 5V between 1 and 3 would be going between reference and ground, .72V would be between signal and ground, and 4.47V would be between signal and 5V? Sorry, just putting that together in my head.

Calling a PCM is never easy... Are we missing anything?

Not that I can think of. I've been leaning toward a PCM too, was looking for your expertise to verify.
What's a good source for PCM's?
Should I buy a rebuilt?
Or send this one in for rebuilding?

raballard@aol.com wrote: What's a good source for PCM's?

Man, I wish I knew! Even the new or reman PCM's of this generation are known for problems. I'd be inclined to get it from a local parts store, so you have a human being to deal with, and some kind of warranty if your replacement computer has other problems.

I don't know that we're missing anything so far, but I'm happy to hear from anyone else following along if I've overlooked something. Wondering if it's worth taking the PCI bus wires out of the PCM connector and rechecking for communication, just to eliminate the network from the equation.

Last I checked, I could not communicate with the PCM through my scanner. And everything was plugged in. My meter did not die, just showed 0 RPM while cranking.

I'm still confused by this. I'm not nitpicking here, but if you can't communicate, what are you looking at for an RPM pid?

I may be biased, but I don;t have problem with used PCMs from the salvage yard. Sometimes a good used factory part is better than a brand new Made In China unit.

Are you using a diagram or pinout to ID the pin numbers?
This would be disconnected, front probed....
I think...
definitely check the colors of the wires to be sure.

I've got 4.47 volts between pins 1 & 2. 5.17 between 1 & 3. and .72 between 2 & 3.

So with 1 being signal and 2 being sensor ground, 4.47v seems high, but plausible.
1 being signal and 3 being 5v supply 5.17v I cant quite make sense of that yet
2 being ground and 3 being 5v supply, .72v says red flag

Just check them all with the negative lead of your meter on the negative post of the battery, and if you think of it, post the readings with the wire colors please.

Also could someone post a schematic of this Pci Bus system? I don't have one but if someone could post it I might be able to help with this. I have quite a bit of experience working with no Comm issues on Buses. This might be a little different, but the concepts still apply here.

This is all I could get BusJockey

I've got 5.2 V on the orange wire.
.72 on the orange/blue.
And the black does seem to be a good ground.

raballard@aol.com wrote: I've got 5.2 V on the orange wire.
.72 on the orange/blue.
And the black does seem to be a good ground.

OK, cool. That seems to be normal. I was confused by the way it was posted before, thanks for clearing that up.
Like Tyler mentioned before, it's never easy to call a PCM.

Probably won't help in this case, but I like to open them up and sniff around for that tell tale burned electrical component smell.

Do you have communication with any other module?
I like Tyler's idea here:

don't know that we're missing anything so far, but I'm happy to hear from anyone else following along if I've overlooked something. Wondering if it's worth taking the PCI bus wires out of the PCM connector and rechecking for communication, just to eliminate the network from the equation.

Guess the bus is the last item to eliminate. How do I check it?
Remember all I have is a multi meter and an error code reader.

Have you checked the comm lines? Can you guys post a schematic of it? Don't know what system were working with. I check the comm lines for integrity first before calling a pcm.

OK. Not sure how to do that though.
I've only got a multi meter and a code reader.

Their are some checks you can do with a dvom and a test light to check the wiring integrity of the comm lines. Hopefully the other guys can find and post some service info on the comm system. One test you could do is for now till we figure out what system your working on is to take your red meter lead and backprobe each comm line while having your black lead on battery negative. Tell me what your DC volt levels are for each comm line and will go from there.