CAN 101, Paccar, KW, PB, all makes

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CAN 101, Paccar, KW, PB, all makes

Post by campbell.kwtech »

To Pico or not to Pico, it's not gallo🐓, its the question.

Concerning CAN diagnostics, before I even think about connecting Picoscope I always perform the traditional trouble shooting CAN checks. Picoscope isn't going to help you if you haven't first confirmed the basics.

Many times I have identified problems with the physical layer without ever connecting Picoscope. Although many times intermittent issues with the physical layer can not be detected without Picoscope.


The basics:
At the bare minimum a CAN device needs Power, Ground and the CAN. The device may have a battery circuit AND or a ignition circuit.

Do you have 60 ohm's on the CAN with the key off? (2, 120 ohm terminating resistors), Are the voltages on CAN Hi and CAN LOW within specifications with key on? Is CAN Hi or CAN LOW shorted to ground with key off or key on? Is CAN HI or CAN LOW shorted to a high source with key off or key on?

Sleeping Beauty
Paccar: Kenworth and Peterbilt have Cab Controllers (ICU, CECU, VECU). If the Key is off and the the door is not closed, these devices will not go to sleep, which will prevent you from confirming the proper resistance on the CAN. To confirm CAN resistance everything on the CAN must be turned off or in sleep mode, this applies to ANY CAN!

More on Sleeping Beauties
The Battery Monitoring Systems (BMS) on the CAN. A BMS (with a Kenworth KIMS System) on the S_CAN (late 2018 or newer) needs to have the 2 fuses removed in the Auxiliary Battery Box or the BMS must be disconnected (note: a 120 terminating resistor is in this module. Prior to 2018 the KIMS CAN was connected to the F_ CAN for a short time, and prior to 2016 the KIMS CAN was a private CAN only. Regardless of the year for the BMS, if the BMS module isn't powered down it won't go to sleep. This also applies to the BMS on the Starting batteries when checking the B-CAN for 2018 J1939 Architecture. When it comes to modules, the list goes on, review the CAN architecture to ensure all the devices on those CANS are going to sleep with the key switch off or removing the fuses or closing the door.

From Earth to Uranus:
Back to basics, check the batteries and connections. Ground is good, or earth as you will. A poor ground or no ground to a device may actually be the root cause of it all. Failing to identify a ground issue can lead you to that far away planet Uranus. Prove Ground (Earth) to be good.

The power of it all
Are the batteries charged properly?
Proving proper Battery voltage to the CAN device. Monitor the voltage, to the device with a VOM ( multi- meter), next apply a load, a good load is a headlamp, it shouldn't draw more than 3 1/2 amps more or less. The voltage drop shouldn't be significant from the unloaded voltage, it may even drop 1 volt depending on wire gauge, in most cases the voltage drop is less than 1/2 volt. Use battery ground and the device ground for comparison in voltages loaded and unloaded.

Finding NEMO:
If the basic CAN checks all prove to be good: power, Ground and the CAN, then it's time to find NEMO, Network Errors, can be found while Monitoring with a Oscilloscope, Motivated Optimism. Picoscope is the best!

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