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[TSB][Engine] "nObuS" appears in odometer, engine will not start

66K views 32 replies 12 participants last post by  Slik08vato 
#1 · (Edited)
Vehicles:
1997 - 1999 Dodge Durango 3.9L
2000 - 2001 Dodge Durango 4.7L
1997 - 2000 Dodge Durango 5.2L
1997 - 2001 Dodge Durango 5.9L
1994 - 1999 Dodge Dakota 3.9L
2000 - 2001 Dodge Dakota 4.7L
1994 - 2000 Dodge Dakota 5.2L
1994 - 2001 Dodge Dakota 5.9L



Symptom: Engine will not start. Gauges are inoperative. nO buS message displayed on odometer.



System: Body/Chassis Electrical, Emissions/PCM/Fuel, Engine Electrical



Codes: N/A



Problem 1 of 6:
The 5v power supply from the Powertrain Control Module (PCM) is shorted due to a shorted Crankshaft Position (CKP) Sensor.

Test & Fix: If the 5v power supply circuit is shorted to ground, the CCD bus is unable to transmit messages and the Powertrain Control Module (PCM) appears to be "dead". The PCM is not damaged when the 5v power supply gets shorted to ground, but does need to be reset by turning the key off for 10 second after the short is removed. Using a DVOM or labscope, measure the voltage on the 5v reference wire at the Throttle Position Sensor (TPS) or Manifold Absolute Pressure (MAP) sensor. If 5v is not present, unplug the Crankshaft Position (CKP) Sensor. Turn the key off for 10 seconds. Turn the key on and measure the voltage on the 5v power supply circuit. If the voltage is now 5v, replace the CKP sensor.



Problem 2 of 6: The 5v power supply from the Powertrain Control Module (PCM) is shorted due to a shorted Camshaft Position (CMP) Sensor.

Test & Fix: If the 5v power supply circuit is shorted to ground, the CCD bus is unable to transmit messages and the Powertrain Control Module (PCM) appears to be "dead". The PCM is not damaged when the 5v power supply gets shorted to ground, but does need to be reset by turning the key off for 10 second after the short is removed. Using a DVOM or labscope, measure the voltage on the 5v reference wire at the Throttle Position Sensor (TPS) or Manifold Absolute Pressure (MAP) Sensor. If 5v is not present, unplug the Camshaft Position (CMP) Sensor. Turn the key off for 10 seconds. Turn the key on and measure the voltage on the 5v power supply circuit. If the voltage is now 5v, replace the CMP sensor.



Problem 3 of 6: The 5v power supply from the Powertrain Control Module (PCM) is shorted due to a shorted Manifold Absolute Pressure (MAP) Sensor.

Test & Fix: If the 5v power supply circuit is shorted to ground, the CCD bus is unable to transmit messages and the Powertrain Control Module (PCM) appears to be "dead". The PCM is not damaged when the 5v power supply gets shorted to ground, but does need to be reset by turning the key off for 10 second after the short is removed. Using a DVOM or labscope, measure the voltage on the 5v reference wire (5v power supply) at the Throttle Position Sensor (TPS) or Manifold Absolute Pressure (MAP) Sensor. If 5v is not present, unplug the MAP sensor. Turn the key off for 10 seconds. Turn the key on and measure the voltage on the 5v power supply circuit. If the voltage is now 5v, replace the MAP sensor.



Problem 4 of 6:
The 5v power supply from the Powertrain Control Module (PCM) is shorted due to a shorted Throttle Position Sensor (TPS).

Test & Fix: If the 5v power supply circuit is shorted to ground, the CCD bus is unable to transmit messages and the Powertrain Control Module (PCM) appears to be "dead". The PCM is not damaged when the 5v power supply gets shorted to ground, but does need to be reset by turning the key off for 10 second after the short is removed. Using a DVOM or labscope, measure the voltage on the 5v reference wire (5 volt power supply) at the Throttle Position Sensor (TPS) or Manifold Absolute Pressure (MAP) Sensor. If 5v is not present, unplug the TPS. Turn the key off for 10 seconds. Turn the key on and measure the voltage on the 5v power supply circuit. If the voltage is now 5v, replace the TPS.


Problem 5 of 6: The 5v power supply from the Powertrain Control Module (PCM) is shorted due to a shorted wire.

Test & Fix: If the 5v power supply circuit is shorted to ground, the CCD bus is unable to transmit messages and the Powertrain Control Module (PCM) appears to be "dead". The PCM is not damaged when the 5v power supply gets shorted to ground, but does need to be reset by turning the key off for 10 second after the short is removed. Using a DVOM or labscope, measure the voltage on the 5v reference wire at the throttle position sensor (TPS) or manifold absolute pressure (MAP) sensor. If 5v is not present, unplug all sensors that are connected to the 5v power supply and disconnect the PCM. Check if either 5v power supply circuit is shorted to ground using a DVOM. If the circuit is found to be shorted to ground, repair the wire and the cause of the short.



Problem 6 of 6:
The 5v power supply from the Powertrain Control Module (PCM) is shorted due to a shorted Governor Pressure Sensor.

Test & Fix: If the 5v power supply circuit is shorted to ground, the CCD bus is unable to transmit messages and the Powertrain Control Module (PCM) appears to be "dead". The PCM is not damaged when the 5v power supply gets shorted to ground, but does need to be reset by turning the key off for 10 second after the short is removed. Using a DVOM or labscope, measure the voltage on the 5v reference wire at the Throttle Position Sensor (TPS) or Manifold Absolute Pressure (MAP) Sensor. If 5v is not present, unplug the large round connector on the driver's side of the transmission. Turn the key off for 10 seconds. Turn the key on and measure the voltage on the 5v power supply circuit. If the voltage is now 5v, remove the transmission pan and check for shorted wiring inside the transmission. If the wiring is OK, replace the Governor Pressure Sensor.
 
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#2 ·
Another common issue with the "no bus" warning is a missing ground wire. Dakotas and Durangos have ground wires on two sides of the firewall, as well as the inside both front fenders. If any of these are removed in the process of removing other components, this error will occur.

Follow the harness in both directions from the ECU, and look for any wires that are not attached.
 
#6 ·
Ive got this problem right now. My odometer says NO BUS and my durango will not start. Ive replaced the PCM so thats not my problem. Ive checked the sensors, all except the govenor sensor. Does anyone know where the connector for it is? Ive looked under my durango but i still cant find the connector. Is there a pic that shows exactly where its at and what it looks like?
 
#8 ·
Thanks alot but i was wanting to get some knowledge on the actual connector that sits on top/outside of the tranny. I know it is a 8-way connector that routes up to the engine compartment but i dont where exactly it is,lol. Ive searched online and have seen that if i had a short in the tranny to disconnect the 8-way connector but i have no idea where its at :)
 
#9 ·
Hello all,
For some reason this post caught my eye.

I am an industrial controls engineer and currently do a lot of sub contracting for the big three out here in the D.

I have just recently seen the NO BUS error in my brothers Dodge Neon, had the same issue. I actually swapped his ignition relay with his AC Clutch relay (same relay number) And confirmed his ignition relay was garbage..... Why it displayed this on his dash and that being the cause? Um.. Not sure how the engineer who designed the fault code for his vehicle setup the alarms (which are hard programmed ladder logix in your vehicles main control center, i guess the ECM / PCM / etc etc)

Typically though a NO BUS fault is a fault that is saying, hey! I do not have BUS POWER (as in there is no communication power) thus, NO BUS, or BUSS OFF type of faults will be displayed. Allen Bradley's PLC controll modual cards have a similar function... So if you are getting a no bus fault.. I would think you may need to sit down with a print and actually figure out if you have a FUSE, a RELAY, a WIRE, or MODUAL issue.

99 percent of the time if its a RUNNING and fully funct. system,
its likely a FUSE, RELAY, or MODUAL issue. If not, obvious thing is a GROUND or perhaps even any variety of WIRE thats being fed in that electrical system between ignitions point A all the way to the main MOD being point B.

Having designed a lot of fault code... its strange to think how engineers have done the SAME thing for vehicles... To be honest it makes my mind hurt because some of it was just poorly designed and is junk........

Hope my post was worth while to someone though!
 
#10 ·
Unfortunately, as these vehicles age, more electrical issues are coming up with the primary one being the "no bus" error. But like you said, this error comes up with a variety of causes. The most common, that I have seen is the ground wire under the stock air cleaner, or the ground wire in the drivers side fenderwell is removed while working on something. But the ground wires under each side of the dash can also cause this fault.

Schematics can be found at

http://search.ebscohost.com/

log in as User ID: tech Password: tech
 
#12 ·
Wow you people really sound like you know what you're talking about :) i havnt got my Durango to start ever since i got the NO BUS issue back in july of last year. Ive put SO MUCH money in my durango youd think it was brand new. Lol. When you said module when you were listing the possible causes off the NO BUS im having what are the modules? Im sure you see what ive already changed or checked but im not mechanically inclined so teach me what i need to know in order to get my durango back running
 
#13 ·
Well, its no bus, so... somewhere in your ECM or PCM mods, could be anywhere in the main feed of that, but that's just my best based assumption. Check ground / 24VDC / 0VDC lines on the ECM and PCM, might need to dig out the pin-out and schematics on it, will make it easier.
Would be a place to start I suppose?
You may test it all out and it works just fine,
well,
isn't that a head ache ? :\

If that's the case,
and it all tests ok,
look in your entire ignition system wiring and verify your main ignition starting circuit is proper and good (ignition relays, solenoid's, grounds, battery connections, etc.)
 
#14 ·
Ok. I removed the gps and solenoid from the tranny and also disconnected the middle connector on the pcm and the no bus goes away and my fuel gauge and battery gauge works but when i reconnect the middle connector the no bus comes right back. Is it because i dont have a gps or solenoid connected THAT ISNT BAD when i have the 2nd pcm connector connected? Or is it something else?
 
#15 · (Edited)
The middle connector contains the +5v lead that is shared by all those sensors listed above. So the fact that it works until you plug the middle connector in indicates that the PCM is good but you do in fact have a short in that circuit somewhere... If you have checked/replaced ALL of those sensors, then you have a wiring harness that has chafed/melted somewhere and the wire is directly shorted to ground..

Just to rule out an oversight, do step 5 again.. Unplug ALL of the sensors (TPS/MAP/CKP/CMP/GPS) and then plug the middle connector back in and see if it still says nobus. If it does, you have a shorted wire. If it doesn't, plug the sensors back in one by one until it faults again.
 
#16 ·
I know the 1st connector to the pcm has a 5volt supply but i think the 2nd connector has a secondary 5volt supply also. Do you have any suggestions on what wire in the 2nd connector could be the problem? I hear that the 2nd connector is a common problem when it comes to a no bus, no start issue.
 
#17 · (Edited)
The +5v (18ga orange) in the middle connector is for the GPS.. However if you have the 8-pin connector unplugged from the trans, that can't possibly be it. I didn't realize they used a separate pin on the PCM for it (even though it is connected to the same +5v source as the one in C1), I thought they were all on the same pin..

C2 contains nothing else but the injector drivers (ground output - would throw a P020x if shorted), sender inputs (ground input, would simply peg that gauge/reading high if shorted), three transmission solenoid outputs (ground outputs, but they go through the main trans connector), one transmission relay output (ground output, would throw a P0702 if shorted), and the alternator field (ground output, alternator would be putting out over 19v if shorted). There are no other power wires or bus wires in that connector.

I betcha if you test the orange wire (pin31) with the transmission unplugged, you will find continuity to ground - indicating it is shorted..

 
#18 ·
Um how do i check for continuity? Do i connect the dvom to the tranny fuse connections where the fuse would go or directly to the wire that supplies the 5v supply on the middle pcm connector? And would it be safe to say that the gps is what is shorted?
 
#20 ·
No, test for continuity/low resistance between pin 31 on the harness and the chassis. If there is continuity or any resistance lower than a megohm, then the wire is shorted to ground somewhere. I just re-read your posts - did you ever get the 8-way connector unplugged from the trans?

If you have the GPS out and/or the 8 way connector unplugged when doing these tests, then no it is not safe to say it's the GPS.. How can a part that's unplugged be causing a short??

TazRango, if I unplug the center connector on the PCM and the no bus does not go away, would you recommend replacing the PCM or is there something else you recommend to try?

The vehicle died, then started again, then died on the interstate. Spedometer went from driving speed to over 120 and danced around before it died. Now no gauges work, will not start, and no bus error is displayed.
No, because the +5v in C2 only feeds the GPS. The primary +5v wire that feeds the sensors is in C1. However you can't test by unplugging C1 because C1 also contains the battery and ground feeds for the PCM. Did you go through and unplug all the sensors listed and see if the nobus goes away? Then plug them back in one by one until it comes back?
 
#19 ·
TazRango, if I unplug the center connector on the PCM and the no bus does not go away, would you recommend replacing the PCM or is there something else you recommend to try?

The vehicle died, then started again, then died on the interstate. Spedometer went from driving speed to over 120 and danced around before it died. Now no gauges work, will not start, and no bus error is displayed.
 
#21 ·
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.
 
#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.
 
#23 ·
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 :)
 
#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.
 
#26 ·
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?
 
#27 ·
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
 
#28 ·
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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