In my experience a DVM is too slow for CANBUS testing. You can have a shorted CAN high or CAN low and it’ll still show correct voltage. A scope is the appropriate tool for correctly diagnosing CANBUS issues.
I agree. This was just meant to show basic CANBUS diagnostic. The DVOM can be very effective for certain tests though in my opinion. Quick measurements to verify circuit integrity. If you are trying to see modules communicate, the scope is the correct tool.
one thing I have never been able to get an answer for about CAN networks is where does the bias voltage come from? What module is responsible for maintaining that 2.5v bias on the network? I had a ford transit van in my shop a few weeks ago with the entire power-train high speed CAN1 network down. No communication, no bias at all(none and the DLC, none on the back of the gateway module and none at the ECM). I requested more diagnostic time and the customer refused since the vehicle have over 200K miles on it. So I never got to figure out what was wrong with the vehicle but what I couldn't find out from service data was where did the bias voltage come from. That would have helped me in my diagnosis if I would have know where its origin was. So can you or some one explain that to me.
Not sure if I’m understanding the question fully. Every system is different, But the 2.5 V for the most part I would assume comes from internal circuitry of the gateway module. It’s like any other reference circuit. Internally regulated from the module. As far as that ford you were working on goes. I would guess one of the modules failed internally. Or, a power or ground supply issue to the actual module itself. Or an open circuit. I probably would’ve been looking for something in the wiring harness after I checked all the powers and grounds. Would need to reference a diagram to know how the circuit is laid out.
In my experience a DVM is too slow for CANBUS testing. You can have a shorted CAN high or CAN low and it’ll still show correct voltage. A scope is the appropriate tool for correctly diagnosing CANBUS issues.
I agree. This was just meant to show basic CANBUS diagnostic. The DVOM can be very effective for certain tests though in my opinion. Quick measurements to verify circuit integrity. If you are trying to see modules communicate, the scope is the correct tool.
My pis 14 and 6 are showing 426.3 MV ? Everything else tests good. 2.5 or so.. thoughts?
Nice work! Good job!
Thanks Stahodad, stay tuned! More content coming soon!
@maxwellautomotivellc ...cool..right now my 2 vehicles are pre 2006, so no CanBus, but I know someday I'll have to deal with this stuff. 😉
one thing I have never been able to get an answer for about CAN networks is where does the bias voltage come from? What module is responsible for maintaining that 2.5v bias on the network? I had a ford transit van in my shop a few weeks ago with the entire power-train high speed CAN1 network down. No communication, no bias at all(none and the DLC, none on the back of the gateway module and none at the ECM). I requested more diagnostic time and the customer refused since the vehicle have over 200K miles on it. So I never got to figure out what was wrong with the vehicle but what I couldn't find out from service data was where did the bias voltage come from. That would have helped me in my diagnosis if I would have know where its origin was. So can you or some one explain that to me.
Not sure if I’m understanding the question fully. Every system is different, But the 2.5 V for the most part I would assume comes from internal circuitry of the gateway module. It’s like any other reference circuit. Internally regulated from the module.
As far as that ford you were working on goes. I would guess one of the modules failed internally. Or, a power or ground supply issue to the actual module itself. Or an open circuit. I probably would’ve been looking for something in the wiring harness after I checked all the powers and grounds.
Would need to reference a diagram to know how the circuit is laid out.
check resistance with ignition off? voltage with ignition on? Thanks
Yes, always test resistance between pins 6 & 14 with the key in the off position for an accurate reading. Should see right around 60 ohms.
@@BigDogDiagnostics Correct me if I'm mistaken, but when checking the Canbus, is it not better to remove the ground cable to kill the 12V system?