Sporadic Fault Codes….

Now that's some serious troubleshooting !!!

on the TCM side, unhook the TCM cable and recheck the resistance values.
Measure the resistance from that side and then again from the diagnostic port. Do they match up?

If they match up then I might (loosely might) suspect the TCM resistors.
You can also unplug the data wires at the three locations and test all the wires for continuity.
If you have a broken wire or shorted wire, doing a loop back test will indicate any issues.

this is what I had to do when my tranny push pad went dark. I used paper clip to bridge the wires on one end and loop tested for continuity on the other. this would be a good time to also stress test the data link wires...all of them.
 
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Related issue..

2007 Bluebird Vision/ Engine Comm Failure, Trans Comm Failure, ABS Comm Failure

I have a 2007 Bluebird Vision with a C7 Acert engine and Allison transmission. When I turn the key to the run position (without starting) the speedometer reads engine comm failure, trans comm failure, and ABS comm failure. All of the gauges start sweeping. The bus can be started, however the...
www.skoolie.net www.skoolie.net
 
desrtdog said:
... Found a triangular connector that looked like it could be one next to the ECM on the front left of the engine, but it is just capped…
Click to expand...
I believe that this connector can access the ecm directly. I have a wiring connector that came with my nexiq which I believe will connect to this triangle port. I just can't verify right at the moment since I deleted :mad: my computer OS and have not been able to reload insite on the current OS replacement.
 
I just saw your post about the rat problem you had...is the diagnostic plug under the dash in close proximity to that are visited by the rats?
 
ewo1 said:
Related issue..

2007 Bluebird Vision/ Engine Comm Failure, Trans Comm Failure, ABS Comm Failure

I have a 2007 Bluebird Vision with a C7 Acert engine and Allison transmission. When I turn the key to the run position (without starting) the speedometer reads engine comm failure, trans comm failure, and ABS comm failure. All of the gauges start sweeping. The bus can be started, however the...
www.skoolie.net www.skoolie.net
Click to expand...
I’m not getting anything more specific than “comm fail”…also, gauges do the normal single sweep at ignition on, and bus is cranking, but not starting…
ewo1 said:
I just saw your post about the rat problem you had...is the diagnostic plug under the dash in close proximity to that are visited by the rats?
Click to expand...
Have not had any rat problems - was this from @PorchDog by chance?

Follow up from earlier:
  • Disconnected batteries and rechecked J1939 resistance at diagnostic plug: 42.5 ohms
  • Pulled the TCM (thus removing the terminating resistor at that end); harness connector and pins all looked fine, no loose wires in the connector.
  • Checked J1939 resistance from the diagnostic plug and initially got ~90 ohms; checked TCM resistance across pins 7&8 and got 110 ohms with some slight variation (moving upwards at 0.1 ohm increments to 112 ohms
  • Checked resistance on J1939 from TCM connector side: 113.5 ohms; rechecked from diagnostic plug: 113.7 ohms
  • Reconnected TCM batteries; resistance across diagnostic plug now 55 ohms.
  • Ran some checks on the speed sensors from the ABS module connectors and got no continuity … supposedly should read 1500-2500 ohms on the sensors, so might have messed this test up, or might have a problem with the ABS wire harness??? Ran out of time for the day, so need to look at this a bit more.
After all of this, no change - still have a comm fail issue and bus cranks but doesn’t start…
 
desrtdog said:
I’m not getting anything more specific than “comm fail”…also, gauges do the normal single sweep at ignition on, and bus is cranking, but not starting…

Have not had any rat problems - was this from @PorchDog by chance? My bad, wrong dog...lol

Follow up from earlier:
  • Disconnected batteries and rechecked J1939 resistance at diagnostic plug: 42.5 ohms Ideally it should have read 60 ohms... allowing for a 10% tolerance of 12 ohms...(per side) or 6 ohms in total (both sides-measured in parallel). I would double check your battery in the meter. When they go low DMM will not read accurately
    • Pulled the TCM (thus removing the terminating resistor at that end); harness connector and pins all looked fine, no loose wires in the connector. great news!
    • Checked J1939 resistance from the diagnostic plug and initially got ~90 ohms; checked TCM resistance across pins 7&8 and got 110 ohms with some slight variation (moving upwards at 0.1 ohm increments to 112 ohms At the end of the day you got 110 ohms which is good but what is puzzling is why did it take time to build up to that value, started at 90 ohms. Makes me suspicious of a loose or corroded connection somewhere. This goes back to stress testing individual wires...but then again it could be an indication of weak batteries in your DMM or a possible short/moisture in the wiring.
    • Checked resistance on J1939 from TCM connector side: 113.5 ohms; rechecked from diagnostic plug: 113.7 ohms If you were testing the resistors independently, then these values look real good! well within the 10% tolerance expected. Even if they were 5% resistors, values still look good.
    • Reconnected TCM batteries; resistance across diagnostic plug now 55 ohms. This looks about right!
    • Ran some checks on the speed sensors from the ABS module connectors and got no continuity … I would strongly suspect this is your problem, no continutiy equals no communication! supposedly should read 1500-2500 ohms on the sensors, so might have messed this test up, or might have a problem with the ABS wire harness??? I would take a closer look at why there is no continuity! Ran out of time for the day, so need to look at this a bit more.
    • After all of this, no change - still have a comm fail issue and bus cranks but doesn’t start…
Click to expand...
My thoughts above, in red...

That was even better troubleshooting !!! I wonder how much that would cost at a shop!​

As far as terminating resistors are concerned, I think you are in a good place. values are within spec.

That fact that you found no communication from the ABS module to the sensors...that need to be explored and find out why!
Could it be that when the condition of no ABS communication appears ECU goes to a NO START condition as a fail safe ???​

I would make sure your batteries in the DMM are fresh.

Wherever you can stress test the wires ESPECIALLY if and when they are going thru a connector. At a connector is the most probable source of a bad connection followed by crimped/pressure damage wires especially when there is some sort of clamp or wire tie holding it in place.

You are doing great and are for sure on the right track!​

Not to add any stress or anything but in the end, if after all the checks are done, you might want to think about testing your ECU on another bus or or re-flashing yours. we are still miles away from that option....

The fact that the ECU is still doing post self test and cranking the engine is very promising...
 
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desrtdog said:
I have a Bendix system, but no problem…

Also, thanks for the encouragement … this thing is beating me down!
Click to expand...
Your doing great...!!!

Not only are you 100% verifying everything but..

You are learning about your bus. Knowledge is powerful especially when you breakdown.
Your saving a ton of money, no shop monkeys guessing on your dime!

I feel confident that you will get this!

Doc: Bendix School Bus Brake system Troubleshooting
 

Attachments

  • BW1640_US_004-Bendix school bus system troubleshooting.pdf
    721.7 KB · Views: 6
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related issue...for general reading/info
The J1939 on Blue Birds with C7s (Visions at least) is prone to failure. From what I've seen and heard, it tends to get pinched somewhere behind the engine and has a failure.........
Click to expand...
It is not a cut and splice type circuit. The circuit has to have interference free signals. One butt connector or the wires not being twisted can cause major issues.
Click to expand...


Remote Diagnostic Units (RDUs) and Trailer Remote Diagnostic Units (TRDUs)​

I have no clue on this other than to say I researched it as it was mentioned in the schoolbusfleet thread.

Remote Diagnostic Units

www.bendix.com www.bendix.com
 
You mentioned this earlier...
Disconnected batteries and rechecked J1939 resistance at diagnostic plug: 42.5 ohms
Click to expand...
and when you disconnected the TCM you got better readings, 42.5 ohms while being close to the 10% tolerance of 60 ohms, 10% of 60 is only 6 ohms. so theoretically 54 ohms is where the 10% tolerance should be... just for thought while testing.... but again, with the TCM disco from the circuit you got better reading. i do not think that the total impedance of the TCM, while in circuit, would cause the numbers to change much if at all... Otherwise testing for 60ohm on a closed circuit would not be a OEM recommended test.

Gives me a bit of reason to think that maybe your datalink circuit is being pinched...small maybe...keep the thought in your head as you go thru the wiring....

Keep your eyes open...
 
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I have talked about but don't know if YOU know what "Tolerance" on a resistor means...

Tolerance
The tolerance band on a resistor indicates the acceptable range of variation from the stated resistance value. It represents how much the actual resistance may differ from the nominal value due to manufacturing tolerances. Resistors are rarely made to perfect precision, and tolerance bands account for this.

Mil spec/medical resistors would be well under the 1% tolerance where industrial equipment is usually either 5% or 10%.
 
Talked to a couple of mechanics today - the one I initially used in Lubbock when I bought the bus, and another guy in the checkout line at the gas station who has 30+ years experience with Freightliner chassis, Thomas busses…consensus from both is that the ABS issue is not related to the crank/no-start (I was wondering if there might be some sort of interlock on starting if ABS system not working, but not so…Their opinion was the no start seemed more of a fuel delivery issue, asked if I could hear the low pressure pump actuating at key on (can’t hear anything over the piercing warning beep)…the Lubbock mech said to look for a sealed relay/fuse associated with the fuel pump … said to try putting a gas soaked rag at the air inlet to see if the bus would turn over (haven’t tried that yet)…

As far as the comm fail and ABS go, I rechecked resistance on the wheel speed sensors - they all checked out fine (~1800 ohms)…turns out I did not have the correct rang setting on the meter yesterday… Cleared (or think I did) the ABS error codes using the diagnostic button… Still have the comm fail and ABS light though…thinking maybe related unless there is some other J1939 module not talking….
 
If you want to be bold and try to start it using SILICONE spray, not starting fluid....
That might to some degree tell us if it is a fuel delivery issue but then if we go back to step one, the stalling of the motor. ECM power loss... If it is an ECM communication issue then she won't start...

Interesting....

After all we have looked at, I don't remember if you have Cummins Insite or not... If you do, will it talk to the ECU?
If we can talk to the ECU then we know the datalink is somewhat operational.
If you cannot talk to the ECU...well, no bueno....
 
I found this Cummins troubleshooting tree...

Engine Performance Troubleshooting Tree - CM554 Electronic Control System with CAPS Fuel System

Some really good troubleshooting steps/info...
 

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  • troubleshooting-tree.pdf
    256.1 KB · Views: 5
Found another troubleshooting doc. This on is really comprehensive and probably a sidetrack on your efforts right now but it does have an interesting section (pdf page 143) that deals with ECM ground noise and it's effect on the system.
I would save this for future reference but still briefly skim thru it to see if there is anything of value-help for your current dilemma.

It is 14 Mb so too large to upload..

Cummins Electronic Troubleshooting

ECM/GM and AGE Tests
 Reduce potential mechanical issues resulting from too much current going through the block before returning to battery
 Recued the amount of “electrical gremlins” or No Trouble Found service calls
 Devices may have trouble when a discrete signal is interpreted as on when it is off (or vice versa)
 These tests become more important as more electronics are added to our engines and vehicles overall
 
ewo1 said:
If you want to be bold and try to start it using SILICONE spray, not starting fluid....
That might to some degree tell us if it is a fuel delivery issue but then if we go back to step one, the stalling of the motor. ECM power loss... If it is an ECM communication issue then she won't start...

Interesting....

After all we have looked at, I don't remember if you have Cummins Insite or not... If you do, will it talk to the ECU?
If we can talk to the ECU then we know the datalink is somewhat operational.
If you cannot talk to the ECU...well, no bueno....
Click to expand...
Comments:
  1. Yeah, Lubbock mechanic said no starting fluid, but a gasoline soaked rag at the air inlet should get it to fire up from the fumes…
  2. I tend to think that the datalink is talking to the ECU - maybe just wishful thinking though… I did notice from the Cummins engine wiring diagram that there is another couple of pins to Engine ECM connector (the other 60-pin connector on the ECM) as well as what is shown to be a 120 ohm resistor attached by a connector…OEM connector to J1939 via pins 1 & 21; Engine connector to J1939 via pins 38 & 39…
  3. Wondering if the comm fail is related to the ABS error code 11/2 - J1939 Retarder…. What is the retarder and where is it??
 
ewo1 said:
I found this Cummins troubleshooting tree...

Engine Performance Troubleshooting Tree - CM554 Electronic Control System with CAPS Fuel System

Some really good troubleshooting steps/info...
Click to expand...
CAPS not applicable to my engine - it has a high pressure common rail…
 
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