Sporadic Fault Codes….

[ewo1]

J1587
In J1587/J1708 networks, terminating resistors are generally not required, unlike J1939 networks. J1587 utilizes a two-wire bus for communication, and proper wiring and testing are more crucial than terminating resistors.

• No Terminating Resistors:
  Unlike J1939, which requires 120-ohm terminating resistors at the ends of the bus, J1587/J1708 does not typically need these.
• Bus Termination:
  Proper bus termination in J1587/J1708 is achieved through correct wiring, ensuring proper voltage levels and continuity checks.
• Testing:
  To verify proper bus termination, you should measure the voltage between the J1587+ and J1587- terminals relative to ground. The voltage should be within specific ranges (e.g., 6-11 VDC for J1587+ and 9-13.5 VDC for J1587-)
  
  
  
• Resistance Checks:
  With the key off, you can also measure the resistance between the J1587+ and J1587- terminals, which should be between 3k and 18k Ohms, and between each terminal and ground, which should be more than 1k Ohms
  
  Troubleshooting J1708/J1587 Connections

 

[ewo1]

So this is all new to me. I am just now myself learning about the J1587 datalink.

all you BB vision bus owners need to pay attention...

 

[nikitis]

J1708 has to operate under 5 ohms I believe. I think I remember reading that when i was troubleshooting my VPM Issues. It prefers 5 ohms or less for optimal communication. Beyond that it starts to fail. Troubleshooting diagnostics also states this in the T444E manual for the network.

This is why it is recommended to be in twisted pair wiring.

If his bus is a 2008 he shouldn't be using J1708. I've never heard of a hybrid either.

I found this info in my EGES.

The DCL lines are specific to a 3 box but it carries the same data over it as the ATA signal.

The ATA Lines are the standard J1708 generic twisted pair lines used in all J1708. The ohms requirements are the same across both because they operate at the same frequency transmitting the same protocol.

Ignore the pin numbers / test points because this is for a mid 90's 3Box, won't apply to yours, but the spec requires < 5 ohms. Wiring gets aged over time too and resistance can increase. J1708 is a sensitive network and any noise will interrupt the signal. You may have to even consider adding fresh wiring potentially in twisted pair form.

 

[desrtdog]

My bus is a 2010 model year using J1939, but also has wires for J1587 which I believe are like a read only capability….in any case, the issue I have is either with the J1939 network itself, or the ECM…more on this:

• On Friday, I spoke to Cummins tech service about my issues and their comment was that the ECM itself may be bad…I believe that if I had the bus hooked to INSITE I’d probably know quickly whether the ECM is communicating, but since I don’t have that capability, the recommendation was to pull it and have it bench tested. (Note to @ewo1 - appreciate the offer of the disk…may take you up on that, but would still need to get a laptop for it, plus any other connectors, etc…plus, not entirely sure it will work without some sort of activation from Cummins…)
• Took yesterday off…trying to figure out how to test the J1939 datalink for a short between the wires with my newly acquired ECT3000, and I am not totally convinced it will do the trick, as neither of the two J1939 wires are grounded…
• Went up today to try this…short story is that I could not figure it out. Tried grounding one of the two wires and sending the signal through the other, but all I got showing up was an “open” fault….PLUS…
• Took some more measurements …. Batteries disconnected, TCM pulled, also disconnected the connectors to the VGT (which links to the ECM engine connector at pins 38/39 - which in turn are connected to another terminating resistor per the wiring diagram for my engine - although I have yet to locate said resistor)…
• TCM pin 7/8 resistance ~ 114 ohms (this would be the terminating resistor inside the TCM); TCM harness pin 7/8 resistance ~ 116 ohms (this is connect to the main J1939 backbone and the ECM via the OEM harness); VGT harness (connects to the mystery terminating resistor) resistance ~115 ohms.
• Reconnected the TCM and measured resistance at diagnostic port (pins C/D) ~ 57 ohms…
• So all the above look to be within spec….hmmm…

One thing I did notice when fiddling with the VGT connector - there is a 2-pin plug with a twisted pair wire that is running along side of it…both of these were zip-tied pretty tightly to the turbo oil drain line…when I pulled the loom back from this wire, I noticed that the insulation on the green wire was chaffed, exposing a small bit of the wire itself. This wire pair is for the turbo speed sensor…don’t think it has anything to do with the comm problems, but noted as a need for repair, or more likely replacement of the sensor itself….see attached photos…

All in, no progress in finding the gremlin. I have a call in to someone to see if they can come up and have a look sometime this week, and will continue flailing in the interim….

Edit: noticed from the pic above that the black wire also seems to have some chaffing - did not test that to see if the insulation was breached, but did test the connector, and no indication of a short between the two, but that doesn’t mean there’s not something going on, given vibrations when driving …

 

[ewo1]

• TCM pin 7/8 resistance ~ 114 ohms (this would be the terminating resistor inside the TCM); TCM harness pin 7/8 resistance ~ 116 ohms (this is connect to the main J1939 backbone and the ECM via the OEM harness); VGT harness (connects to the mystery terminating resistor) resistance ~115 ohms.
• Reconnected the TCM and measured resistance at diagnostic port (pins C/D) ~ 57 ohms…
• So all the above look to be within spec….hmmm…

All in, no progress in finding the gremlin. I have a call in to someone to see if they can come up and have a look sometime this week, and will continue flailing in the interim….

Well at least you finally determined that the terminating resistors are ok. If you got 57 ohms, your in spec. this is good.

Did you do this resistance testing with all three units (ECU,TCM,ABS) all plugged in? I guessing you at least had the TCM plugged in otherwise you would not have gotten the 57 ohms.

Have you tested the integrity (continuity) of each individual wire that goes to these three components?
Have you looked at the instrument cluster connection.

So what I am thinking is that the wires connected to the terminating resistors are ok, but what about the other wires to ECU and ABS... If any of the other wires they use for communicating are "open" then that could be a potential reason why "Comm fail" appears.

I got some free time this week, I wouldn't mind the short drive your way to give you a hand... Don't go paying someone just yet for help....
If all the communication wires are individually tested along with power and ground...then I would say yes have the ECU bench tested but if you do that and your bus still won't communicate....

I am gonna try to load Insite on my laptop, I don't know if it your bus is to new for the software I have but...well see..

 

[ewo1]

How would I test the individual wires ???
Unhook the wiring connectors to the TCM, ECU, ABS and Instrument panel.

1) First test for stray voltages and resistance reading on wires , to look for wires that have a resistance reading where/when it is not supposed to have...

2) With a helper at the diag port checking the DMM, and on the other end of the data link, short both datalink wires at each connector to see if the sort appears on the screen.
If you do not see the short then the wire is open and cannot communicate.
If you do see the short then wire is good.

this is how I troubleshooted my tranny push pad when the circuit went dead.

Then there is identifying/testing each and every power/ground for the 3 units (ecu, TCm, & ABS) that need to be 100%.

when doing complex troubleshooting like this one, I find it helpful to have a cheat sheet and notes so i can mark it up with comments as I go along...

 

[desrtdog]

Well at least you finally determined that the terminating resistors are ok. If you got 57 ohms, your in spec. this is good. Not quite sure I’d go that far yet … what is puzzling to me is that the digital multimeter is not steady. Might try to get my hands on an analog one to see if there’s any difference.

Did you do this resistance testing with all three units (ECU,TCM,ABS) all plugged in? I guessing you at least had the TCM plugged in otherwise you would not have gotten the 57 ohms. Only the TCM … had the ABS unplugged a some time, but not with resistance testing.

Have you tested the integrity (continuity) of each individual wire that goes to these three components? Checked each TCM socket for continuity to the J1939 wires (7/ individually - no shorts.
Have you looked at the instrument cluster connection. Pulled that previously; panel does its sweep at key on so think that is ok.

So what I am thinking is that the wires connected to the terminating resistors are ok, but what about the other wires to ECU and ABS... If any of the other wires they use for communicating are "open" then that could be a potential reason why "Comm fail" appears.

I got some free time this week, I wouldn't mind the short drive your way to give you a hand... Don't go paying someone just yet for help....
If all the communication wires are individually tested along with power and ground...then I would say yes have the ECU bench tested but if you do that and your bus still won't communicate.... Yeah, I talked to a couple of places and price ranges from ~ $400 to $800 - higher end being a “fix” which means a reflash

I am gonna try to load Insite on my laptop, I don't know if it your bus is to new for the software I have but...well see.. What is really curious about is whether the ECM shows up on insite…

 

[ewo1]

When you say that your DMM is not steady, elaborate please...
is it bouncing around by just a few ohms or is it just not consistent each time you do a reading?

It is expected for the ohm to move a little especially if there are other components that could be attached to the circuit such as in the case of the TCM terminating resistors. Technically speaking the added circuitry within the TCM could affect the resistance readings but not by much, maybe less than 5 ohms. this is why you also have to factor in the tolerance values...

I know you tested the wires for shorts..
shorts to ground?
shorted to another wire?
Opens must also be tested for. If you only check for shorts to ground or shorts to another wire you can easily miss/bypass an open wire.
An open wire will not show a short.
The reason I made up the "cheat sheet" with the terminal numbers is so that you can completely open up the circuit, apply a short to the pins at each connector location and verify the results at the diag port with the dmm set to continuity.

the fact that the dash gauges are sweeping and the starter is spinning when you turn the key tells us that at least some level of communication the the ECU is occurring.

If you haven't done an OPENS test, i think you should as then you will have fully tested the datalink wiring...then you can look at the ECU...but I would try to start it with silicone spray first before you remove the ECU.

I'll keep you posted on the Software install....

 

[nikitis]

That doesn't look like chaffing to me. It looks like Rats got to your wires.

 

[desrtdog]

Instrumentation manual:

 

[ewo1]

For future reference:

J1708/1587
This protocol will be used only to monitor DTCs from the ECUs as described in Fault Diagnostics (Section
7.3.2.1) No other functionality will be performed in this protocol.

J1939 - TX
There is one communication channel for data communication that complies with CAN 2.0B/SAE J1939
(Controller Area Network).

 

[desrtdog]

That doesn't look like chaffing to me. It looks like Rats got to your wires.

Nah… bus is stored in an indoor RFZ (rodent free zone). That area happened to be in very close proximity to a tight zip tie against a bracket….like really tight. Plus could have been in contact with coolant a year and a half ago when the surge tank developed a crack…

 

[desrtdog]

So, spent a couple of hours today with a phone assist from @ewo1 (many thanks for that!!) going through the J1939 datalink wiring to verify integrity using the cheatsheet he provided in post #80 previously…short version is that all of the terminal tests indicated the datalink is good based on continuity from the diagnostic port when the individual connector pins were shorted together…so appears that we are good on that end, and may be possibly dealing with a bad ECM, as I still have the crank / no start issue and the COMM FAIL message …

Given all of this, I may opt to repeat these tests again tomorrow, because what bothers me is the fact that when I first measure the datalink resistance at the diagnostic plug after disconnecting batteries, but before disconnecting any modules, it comes back low - like in the 30’s. When I reconnected modules today the resistances looked fine - 120 ohms with TCM, ECM and ABS connected, dropping to 57 when I reconnected the instrument panel. And anyway, what is insanity if not continually repeating the same experiment with the expectation that the results will change?

Also, one other thing I was wondering is whether we should also have load-tested each of the lines when the pins were shorted…. @ewo1 - any opinion on that?

 

[ewo1]

So, spent a couple of hours today with a phone assist from @ewo1 (many thanks for that!!) going through the J1939 datalink wiring to verify integrity using the cheatsheet he provided in post #80 previously…short version is that all of the terminal tests indicated the datalink is good based on continuity from the diagnostic port when the individual connector pins were shorted together…so appears that we are good on that end, and may be possibly dealing with a bad ECM, as I still have the crank / no start issue and the COMM FAIL message …

Given all of this, I may opt to repeat these tests again tomorrow, because what bothers me is the fact that when I first measure the datalink resistance at the diagnostic plug after disconnecting batteries, but before disconnecting any modules, it comes back low - like in the 30’s. When I reconnected modules today the resistances looked fine - 120 ohms with TCM, ECM and ABS connected, dropping to 57 when I reconnected the instrument panel. And anyway, what is insanity if not continually repeating the same experiment with the expectation that the results will change?

Also, one other thing I was wondering is whether we should also have load-tested each of the lines when the pins were shorted…. @ewo1 - any opinion on that?

The datalink wiring does not move much current thru the wires...
you tested each individual wire for cross voltage, resistance, and continuity.
There were no shorts to ground.
There were no shorts to other wires.
Each and every wire came back good when we put a short on each one in order to verify continuity.

Although we could not find the actual terminating resistors, we did verify the one inside the TCM as good and like you said, the other resistor value was present at the instrument cluster.

For those following, all the wires in the datalink circuit were tested with the ECU, TCM, ABS and instrument cluster all disconnected from the circuitry which means there was nothing on the wires that could have influenced your readings.

Ideally this would be the perfect time for Insite testing.... but we are not in an ideal world....

To answer your question about load testing the wires... I feel confident in your efforts today. You seem to me to have a real good grasp at what is going on and the steps taken so far...

I am a bit uncomfortable that we could not find the actual resistor...but oh well... that's the way the cookie crumbled...

The resistance values changing like they did when you started...not what I would suspect...but again, with the datalink all clear I am not sure what to think of this just yet..
What just might be a good idea is to contact a Bluebird dealer and see if there parts or service guy know the exact location of the terminating resistors.
I know for sure that on an International they are physically located on the datalink backbone.
To come and find out now that one set is inside the TCM, that has got my head spinning a little. That's not what the Allison troubleshooting manual has for info....

The conversation we had about the gas pedal not responding earlier has got me thinking.... But that would not cause a no comm issue from what I understand. That would cause a check engine light...in the international world.

To sum it all up I wouldn't expect to see any changes if you do go ahead and try load testing the wires. Again, not much current flows thru the datalink but hey, gremlins are designed to be deceiving so what you got to lose? Nothing!

the good thing about the way you tested today, removing the connectors and checking at the pins, if any pins were bad or in question I feel that would have appeared today by virtue of all the abnormal movements they went thru today.

I'm gonna look at the drawing again tonight and come hopefully come up with another way of skinning this cat...I mean Cummins... lol, i'm tired...

 

[desrtdog]

Great - thanks again! I think I’ll look behind the cluster tomorrow some more and maybe start taking the loom off the wire bundles to see if anything becomes obvious.

 

[ewo1]

We talked about the VGT harness.. Well I found this while searching for more info...
Nobody seem to knoe exactly where they are located...

In a 2009 Bluebird Vision school bus with a Cummins ISB 6.7L engine, the terminating resistor for the J1939 communication network is located in the engine harness, not the TCM (Transmission Control Module). It's typically found at the diagnostic connector or near the engine control module (ECM). A faulty or missing terminating resistor can cause communication problems with the ECM

• Location:
  The terminating resistor is usually located at the ends of the J1939 data bus. In Bluebird buses, it's typically near the diagnostic connector or the engine harness near the ECM.

VGT Actuator Harness: The resistor can be found in a blue connector within the VGT actuator harness, often near the DEF tank

too many locations !!!
The J1939 terminating resistors in a 2009 Cummins ISB 6.7 Bluebird Vision bus are typically located at the front and rear ends of the bus's J1939 data network. One might be found behind the radio near the windshield, and the other near the expansion modules under the driver-side fender

Don't stress out about the resistor locations, just providing this info so while you testing you can maybe find them... as long as you get 60 ohms, full steam ahead!!!

 

[ewo1]

Question.
I don't remember if I asked but when you crank the bus does the RPM on the dash move?
the tachometer receives its input signal from the ECU via the J1939 ckt. so, if it moves then at least that function of the ecu is good and the datalink is communicating.

same goes for engine oil pressure. so if you see pressure building while you crank, communicating!
Info on page 641 of vol 2 service manual. That's PDF page 177.

Page 644 of the manual, pdf page 180, outlines the steps for running the onboard diagnostics.
have you tried this out? the required password is on the same page.

If you got NO onboard diagnostic communication and the datalink still checks out good then the very last thing to triple verify is the ECU power and ground.
I know you have undone them and cleaned them but at the end of the day you need to 100% verify power and ground are reaching the ECU.

If it is, then ECU re-flash or replace...

 

[desrtdog]

We talked about the VGT harness.. Well I found this while searching for more info...
Nobody seem to knoe exactly where they are located...

In a 2009 Bluebird Vision school bus with a Cummins ISB 6.7L engine, the terminating resistor for the J1939 communication network is located in the engine harness, not the TCM (Transmission Control Module). It's typically found at the diagnostic connector or near the engine control module (ECM). A faulty or missing terminating resistor can cause communication problems with the ECM

• Location:
  The terminating resistor is usually located at the ends of the J1939 data bus. In Bluebird buses, it's typically near the diagnostic connector or the engine harness near the ECM.

VGT Actuator Harness: The resistor can be found in a blue connector within the VGT actuator harness, often near the DEF tank

too many locations !!!
The J1939 terminating resistors in a 2009 Cummins ISB 6.7 Bluebird Vision bus are typically located at the front and rear ends of the bus's J1939 data network. One might be found behind the radio near the windshield, and the other near the expansion modules under the driver-side fender

Don't stress out about the resistor locations, just providing this info so while you testing you can maybe find them... as long as you get 60 ohms, full steam ahead!!!

So those resistors are like the fugawee tribe….
….you know …. A pigmy tribe of people 2 ft tall running around in 3 ft grass saying, “We the fugawee! We the fugawee!”….

(Apologies in advance if anyone’s offended….)

 

[BamaBus]

I don't remember any response to or discussion of the video showing the no com solution involving the body control module. I guess I'm too lazy to look.

 

[ewo1]

Here is an interesting "related" read, his fix was ECM. States that heat killed 2 of them...

2008 Bluebird eng quit - School Bus Fleet Magazine Forums