Cummins Network Diagnosis

Keith Browning · March 27, 2015

I had a tough one to deal with. A 2013 F650 with a 6.7 ISB CM2350 in for an engine derate, both amber and the red engine lights on. Aside from an EGR valve hanging open there were about 8 fault codes for data update time from the aftertreatment modules, DPF level sensor and the turbocharger actuator. If you are not familiar with Cummins, only sensors mounted on the engine itself are hard wired to the ECM. The SCR system, DPF sensors, SCR level sensor and the turbocharger actuator are all "smart devices" which communicate with the ECM via the J1939 network, or CAN.

Normal diagnostics lead to a faulty turbo actuator. This might make sense if we take into account that it contains one of the two termination resisters. The actuator was working fine however and I had a difficult time diagnosing this intermittent network concern. I took a page from my Ford training and decided to use the oscilloscope to monitor the network and was able to catch it in failure - and luckily it finally stayed broken long enough to diagnose.

Network voltage is normally about 2.6 volts on the CAN+ - I measured 9.8 volts! Using the scope I performed a wiggle test. Then disconnected modules on the network until I pulled the connector for the SCR temperature sensor module and the voltage dropped back to 2.6 volts and all but one code changed back to "inactive."

The reason I posted this is because if you suspect a network problem, Cummins has you monitor the fault code display which has an incredibly slow update rate AND, if the network goes down, your INLINE 6 adapter and Insite will lose connection to the ECM. No joy there and I lost at least an hour screwing around with my scan tool before I realized what the hell was happening. It does not behave like IDS for sure.

Bruce Amacker · March 29, 2015

In addition to this good info, MD/HD trucks have a lot more aftermarket modules that ride on the bus than LD trucks do. Fuel minders, GPS systems, maintenance modules, QuallComm style modules, etc are all a nightmare. Many times the truck will run and drive fine without DTCs but the scan tool won't communicate or drops out. If your scan tool has a "sniffer" function that lists modules on the bus, get familiar with what's normally there so you can identify aftermarket modules quickly. Diag is pretty straight forward- disconnect extra modules until normal communication returns. In an extreme case you may need to overlay the J1939 wires to the ECM and run them directly to the scan tool connector so that only the ECM is on the bus. Also, on IH's, if you pull the ECM power fuse, ID the in/out terminals, and run a jumper wire to the output of the fuse it powers the ECM with the key off. This is a quick way to isolate the ECM and leave all the other modules asleep for a tough bus diag.

FWIW, J1939 (pins C and D in the round 9 pin Deutsche) should be about 2.45v on the low side, 2.55v on the high side, and 60 ohms across the terminals with the batteries disconnected. J1708 (pins F and G) are .1 to 1v on the low side and 3-4.5v on the high side. The voltage numbers for low side and high side added together are generally 5v. Obviously, Keith's 9v was way off base. Aftermarket modules are #1 on the hit list for bus corruption problems but for OEM modules it's a corrupted ABS followed by a corrupted TCM. Unplug or depower these when fighting a bus issue on the J1708 or J1939 busses.

Here's a good example I ran across the other day- a 2010 IH DT with tons of extra modules present. Two ECMs, Navigation module, Electric Propulsion, two scan tools, exhaust brake (not equipped), etc. I know this truck fairly well and we've torn it apart trying to find the aftermarket modules without success. It does have issues with the scan tool- not doing what it's told, perhaps caused by the extra modules. If we power the ECM directly, only it shows up in the sniffer.

tuff57 · April 3, 2015

What do you guys use for the newer f650s we have a few in our fleet and are looking into buying the cables and such, we have cummins insite for the engine but nothing to communicate with the body, is it the ids with a different cable?

Keith Browning · April 3, 2015

Cummins Insite / Inline-6 for the engine
Ford IDS / VCM2 for the Cluster
MD Truck-Wabco software and the COM4 connector for the Merritor Wabco braking system.
Allison transmission, I have no clue.

blown99 · April 5, 2015

Cummins Insite / Inline-6 for the engine

Ford IDS / VCM2 for the Cluster

MD Truck-Wabco software and the COM4 connector for the Merritor Wabco braking system.

Allison transmission, I have no clue.

For the trans, you will need the allison DOC software. You can use the inline 6 for the trans, abs and as you know, the engine.

I can't speak specifically on the engine you are troubleshooting, but, smart actuators do not communicate on the actual 1939. They talk on a private high speed data link like the 1939. This will typically consist of the egr valve, turbo actuator, and ITV. This will be wired direct to to the ecm, the ecm will then distribute that info if needed/as needed to other modules that are on the 1939. 1939 modules would be abs, trans ecu, body controller, engine ecm, and certain body controls for specialized equipment such as a fire truck pumper. A green and yellow twisted pair is no longer specific to the 1939 link anymore. For example, the IH will use the yellow/green combo for the body builder data link. A handy tool to keep in the tool box is the bendix abs communication tester. This plugs into the ata connector. It will light up labeled led lights for each module that is found on each the 1939 data link and the 1708 link.

Keith Browning · April 5, 2015

Hence the topic title "Cummins Network Diagnosis."

Yes, Cummins has its own J1939 network which is tied to the ATA connector but also has another diagnostic connector on the engine and is separate. These Ford trucks actually have 4 networks, J1939 (CAN) HS-CAN, ISO and ATA. All of the other modules on the truck use the other networks. The Cummins ECU gets external data from the Instrument cluster on the HS-CAN. The confusion is that Ford does not call the "truck" J1939 network "J1939" as it is referred to as HS-CAN. Ford calls the Private J1939 network "CAN." Confusing? You bet. Especially when you have to use both the Ford and Cummins wiring diagrams to chase down and identify circuits and connectors.