Hey everyone. My first post on this forum - I figured it would be useful to you guys. I'm a fleet manager for a car sharing organization, and I have a heavy background in vehicle electronics.

This will certainly apply to a 1999 Durango or Dakota with the 5.9L, but I imagine the PCM pinout is likely the same for a range of years and engines.

A friend of mine owns a 1999 Durango 5.9L which recently has been stalling on him. It would only do it after idling in traffic for 20+ minutes, and would nearly never do it while driving at speed. When it stalled, the gauges would hang in their last position for a few seconds, fall to zero, the odometer would flash, then "NO BUS" would be displayed on the odometer. Cranking would not make the truck start. After simply waiting for the truck to cool for about ten minutes, it would start without any hesitation.

I ran through the Dodge flow charts and factory wiring diagrams - and one test painted the picture of what was happening. The PCM regulates battery voltage down to 5v which is used to power its internal logic and power its under-the-hood sensors.

Symptoms:

-Truck stalling, NO BUS displayed
-When the truck is in its working state (starts and runs), 5 volts is present at the violet/white wire at the throttle position sensor with the key in the run position
-When truck is in it's failed (won't start) state, the violet/white wire at the throttle position sensor only has about 0.4 volts at it, with the key in the run position

With that, it is safe to assume that one of two things is happening:

-Either a sensor (crank position, throttle position, etc) has shorted internally, causing an overload on the PCM and causing the 5v rail to fall to nearly zero.

-Or, the PCM's internal voltage regulator is bad, causing no output.

So, let's test it!

First, unplug the PCM connector nearest to the firewall, and pop the back plastic cover off from it.

Locate the violet/white wire at pin 17 (the pins are numbered on the face of the connector). Cut that wire, making sure to leave enough length at both ends for it to be spliced back together again, and strip both ends. See picture below:
fItvPfQ.jpg

In my case, the truck would start and run as long as it wasn't hot, and would stall after getting hot. What I did was join the two wire sections together by twisting them together, plug the connector back into the pcm and run the truck until the engine stalls. Then, when it stalls, disconnect the two halves and measure the voltage at the half that is connected to the PCM. It had fallen to 0.4v without any sensors connected. This proved that the PCM was at fault - it was not supplying 5v to the sensors, or to its own internal logic.

So, I thought - hmm. Well, if this needs 5v to run, and can't internally supply 5v, what would happen if I were to _externally_ supply 5v?

I had an old cell phone charger laying around. It outputs 5v and was rated for 1A. No harm in trying -- the PCM was already toast, the sensors are designed to run on 5v and the charger has an output diode on it's PCB, so current loops shouldn't be a concern.

I reconnected the purple/white wire halves back together, wired the 5v output of the charger to the purple/white wire halves, plugged the charger into the cigarrette lighter and the truck started up without hesitation. I metered the current draw with everything connected - it measured at 740mA, so the 1A-rated charger was good enough to supply everything.

The truck would run forever connected like this, and would stall the moment the phone charger was unplugged - proving it works.

The charger itself is very temporary - it works, but it's not very robust. A $4.99 12v -> 5v @ 3A DC-DC converter has been ordered from ebay and will be installed to make this a bit more robust.

I took the innards of the charger, mounted them into a plastic box, and wired the 12v supply to the charger using the switched 12v line from the PCM. Pictured below, the switched 12v wire from the PCM. Just shaved the insulation from it, twisted a wire around that, wired that through a fuse holder with a 3A fuse (smaller would be better, but the smallest I had on-hand is 3A) soldered it and taped it up, it provides 12v to the phone charger's innards:

cqGkvj8.jpg

The phone charger's innards. Red is my 12v input, black is common (chassis ground), blue is the charger's 5v output:

wEOya4s.jpg
7YyPEdt.jpg

Common (chassis ground) can be grabbed from the black/brown wire on the PCM:
vz4Daf0.jpg

Reattached the two halves of the violet/white wire, with my blue 5v output wire spliced into the violet/white wire, cleaned everything up with some split-loom tubing, and bam - no need to replace the PCM and no need to have a new PCM programmed -- $500(ish) saved!

gHLM7US.jpg
Pl3qT6P.jpg

Now, to replace the silly cell phone charger with the more robust dc-dc converter when it arrives, and the truck doesn't stall anymore!

Have fun!

 

Good info! When mine died, I never thought to look at the voltage regulation circuit!


You can step the 12V nominal down to 5 volts using a 7805 regulator with heatsink attached, , or you can try a Cincon module. I like the cincon modules as they are self contained, but the price shows it.

 

You certainly could use a 7805, but it will be a bit more messy. You will want a decoupling capacitor across its output and a 7805 is a linear regulator - so it will dissipate a lot of heat. If that's what's in the parts-box, so be it - it will work just nicely - but a switchmode dc-dc converter is just a neater solution, at a single-digit-dollars pricetag (under $5 on ebay including shipping, for sealed waterproof ones!)

 

That's why I suggested the cincon. I've tried to blow them up, and they just keep working.

The Cincon part # you want is EC4A01H. It's $17 but will take any input you can throw at it- rated 9-18 VDC but I've used it as low as 7 and as high as 20 volts without a problem.

I use it in my LED controllers to run the microcontroller, and power the LED's with it's compliment, the EC5A-12S15 (9-32VDC input, 15 VDC out, again, rock solid 7-20 in use). I actually had a PCB made to put the modules together.

Oh, and even though it says DC, I bet it would probably take AC. I was feeding it some pretty damn ugly DC (Had very heavy of AC feedline interference) and it was happy as could be.

 

I found this fix to work after trying nearly everything else in the book, however I do have two issues..
1. My fuel gauge drops to E and then floats to F no matter how much fuel is there
2. I get a check engine code for IAC

 

so was that the sanfu, with our stalling issue? cause in my stalling issue it was the Crankshaft Position Sensor, but i now know that if it EVER does that again, i can check that.

 

this is a great post. and good to know that your a computer savy person. i have a 97 dakota with the 5.2L with a 5 speed. which wont go back on the road can you find out the exact what i dont have to have running into the PCM or guide me in the right direction. i have a hayes manual and alldata but neither really brake down what will or wont disable starts and running. I know the majors like crank cam injectors map tps o2s(not nessary but nice on the wallet) im looking to get rid of as mush junk wiring out from under my truck as possable so the water wont short stuff out. im planning to more the pmc in to the glove box over time. and the coil as well please all the more help i can get the better.

 

i replaced the cps less than a month ago and IAC a couple weeks ago. I keep looking for bad grounds but have yet to find one. Mine will shut down after 20 minutes of idle in drive. I can wait for it to cool down and restart or i can plug the 5v supply in and start right away. if it werent for the fuel gauge I'd just run it, but that makes the wifey nervous!

 

I would never use such a fix as not trustworthy/dependable these circuits were not made for the heat under the hood of a car or any water splashed up under the hood of a car also.

A temp fix yes but that's it then get a new PCM my word a mickey mouse fix at best

Just my opinion

 

I tried it on my 1999 5.9L Durango. I had a no bus a few months ago so bought a junk yard ecm from a 2000 Durango 5.9L that worked ok (ck eng light on, funny shifting and no OD). So I put a reman ecm in today. At first it ran great then the ecm heated up and got real erratic, dying, squirrely gauges, etc. So I did a temp 5 V connection to the white purple wire and it started right up. But this fix did not work on the old unit where I had no bus.

The tps and other diagnostics checked out fine.

A replacement reman ecm is on its way so I don't have to rely on the temp 5v fix. But good to know about.