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(DURANGO OWNER)
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Ok i think ive figured out how to check for continuity. I use my dvom and connect the leads to the +5v supply on connector 2 of the pcm with the tranny fuse disconnected and the other lead of the dvom to the negative terminal of the battery.Right! Oh and i could never get to the 8-way tranny connector. There is a bunch of gunk where you said the connector is and i cant see it at all. Im not that familiar with my truck lol. On the gps itself, do you know the ohms that it would be if it was good? Im sure i can use my dvom to make sure its good.
 

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Discussion Starter #22
Yeah you do that with the dvom on the Ohms or continuity setting. If there's a beep (continuity) or any resistance other than ∞ or OL, then there is a short. You said you pulled the GPS out already, right? You do this test with the GPS unplugged. There is no spec listed as far as what the sensor is supposed to read.

You kinda have to pull the 8 way connector out - because that will tell you if the short is in the wire harness or the trans itself.
 

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(DURANGO OWNER)
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Well i went to remove the tranny connector on it and once i touched it the fuel pump kicked on so i looked at the odometer and the no bus was gone even with the middle pcm connector connected. So i removed the tranny connector and started the truck with no hesitation. LIFE IS GOOD :)
 

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Discussion Starter #24
Alright great.. Now clean off the connector and harness, and make sure there's no exposed/melted/abraded wire. Fix if necessary. Also check the wires inside the tranny that go between the 8 way and the GPS to make sure there's nothing there that can short.
 

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TazRango, I unplugged all the sensors around the Throttle Body. I unplugged the Crank sensor. I unplugged the sensor off the tranny located on the drivers side towards the back of the tranney. Question on the camshaft sensor, is it built onto the distributer? If so, I unplugged that as well. The no bus is still there and a vibration is coming from the fuse box by the battery. Here is what I did, I removed the fuel pump relay with all sensors unplugged. No bus went away and guages worked. I plugged the sensors all in one by one. Once I plugged the idle air control sensor in (I know it wasn't on your list of things to unplug), I got the no bus back. Once I replace the relay for the fuel pump, nothing I do makes the no bus to go away.

By removing the fuel pump relay, fuel pump hums and guages work. Once I replace the relay, no bus error returns.

With fuel pump relay removed and I plug in idle air control sensor, no bus error returns.

Thoughts?
 

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Holy crap what have i gotten myself into. I had the same "no bus" code on mine...it would stop intermittently and then the other day it stopped and wouldnt start again so I took it to a local garage and their diagnostic told them that I had a bad PCM. They wanted to charge me 1100 to replace it! I went and bought one online for $150 flashed with my vehicles info and figured it would just be a simple swap...now after reading this I wonder if i just wasted all that money? I guess Ill find out when the new PCM gets in. This just makes me further realize that I know nothing about cars anymore. crap
 

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Engine stalls, fault discovery

The start of this thread got me started on the right track, so I thought I'd share my discovery.

Symptoms: intermittent stall, particularly on hot days, with a/c on. Attempts to restart fail, crank - no run. Also, no fuel pump buzz, dash gauges i.e. fuel, temp. at zero. No Bus in the odometer, thought not right away. Code scanner also has "communication error". After a variable amount of time with engine stopped, (hood-up helps cool off faster), key turned to ON, once fuel pump buzz returns, gauges return, engine will start and run normal until next stall.

The start of this thread made the point that the +5 Vdc sensor bus (there are two, primary and secondary) had to be supplying power to make the sensors work for the engine to run. +5 Vdc primary appears at the PCM connector 1 (black), pin 17. +5Vdc secondary appears at on PCM connector 2 (white), and supplies only the transmission governor pressure sensor (aka gps).

I started off by checking the two ground posts behind the left and right headlights. All good there, though I did take the nut off of the right side to examine for corrosion (minor) and polished the tab with emory cloth.

Then using an insulation piercing probe (expensive T-pin, though it does less damage to the wire) and extra long test leads connected to a voltmeter. I connected the probe to the +5 wire on the throttle position sensor (TPS) and the (-) lead to the frame ground post (w/alligator clip). I put the volt meter on the windshield and closed the hood. Started the engine, turned on a/c, let it idle and hoped it would stall, it did! after about 15+ minutes. When it stalled, the +5 Vdc bus =0 volts.

Now I had to figure out which sensor was short-circuiting the +5 Vdc to ground. Now the engine is stalled, Key On. I opened the hood, probe still on the +5 Vdc wire, pulled the connectors from the throttle position sensor (TPS) and MAP sensor on the throttle body. Volt meter still shows zero. The other two sensors on this bus are more difficult to reach, the crank position sensor (CKS, down by the starter) and cam position sensor (CPS, by the distributor). To be thorough, I decided to check the powertrain control module (PCM) connectors (black, white, gray). I wiggled the wire bundles, no effect. I wiggled the connector housing of C1 (black) and suddenly heard the fuel pump buzz and the voltmeter read +5 Vdc!! Haa! now I had a physical location of failure! But the PCM had cooled enough that the +5Vdc voltage was steady.

I moved the probe to PCM C1 pin 17 and got +5Vdc. Moved the voltmeter (-) to the right-side ground post behind the headlight. Placed the voltmeter on the windshield, re-connected the throttle body sensors (2), closed the hood, started the engine with a/c on and let it idle. With the engine compartment pre-heated, it didn't take as long to stall the second time. Sure enough, engine stalled, +5 Vdc bus =0 (now measured at the PCM. Opened the hood, flexed (slightly) connector C1 up against the PCM housing and the voltage came back (and fuel pump buzzed). Flexed the connector slightly down against the PCM housing and the voltage =0. Now I'm certain that there is a heat related open circuit fault on the +5 Vdc line inside the PCM.

After removing the connector hood on C1 (after cutting away the tape with scissors, don't use a knife!) I repeated the test a third time and wiggled just the +5 Vdc wire (after the engine stalled and bus voltage=0). No effect. [I also tested the B+ (aka 12 Vdc) power input to the PCM, to make sure the PCM had the power supply it needed.] So now I'm certain the open circuit is not the wire connector. Now I'm confident the fault has to be inside the PCM, not something I want to take on the liability to fix (though possible to do, it's just solder).

I decided to use Cardone for repair and return service of my PCM at my local Car Quest shop. I've requested they return the PCM I've shipped to them so I don't have to pay extra for reprogramming. Won't know till I get it back if they paid any attention. This process will take longer than an exchange, though hopefully cheaper.

Btw, Dodge dealer "guessed" the PCM was at fault, no guarantee of repair, for a price quote of $1,200. Cardone will do R&R for $350 plus shipping.

Thanks for reading my post. Questions are welcome, though I may be slow to respond. (noob)
Good luck, I needed it and so will you ;)
Disclaimers: past performance is no indicator of future success, your mileage may vary, batteries not included, all available factory manuals where used in the course of this diagnostic, I am not a professional. All complaints referred to Dewey, Cheatham & Howe.
 

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casias
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330 Posts
Excellent post. As these systems age, electrical issues will come up. The more information the better.

I hope all goes well with your ecu repair.
 

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Discussion Starter #32
That would indicate you most likely have a bad PCM.
 
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