Bus bias voltage is shifted low. More noticeable when key in Accessory position and less bus activity. Looks like this
When full activity with KOEO it looks good likes this.
Trying to come up with diagnostic strategy to find the issue. Is that the sign of a weak node?
My first step would be to look at ignition voltage pids on modules data
Most likely a bad module. Check ohms at #6 & #14 on the obd ii connector. Should be 120 ohms if all is well. 60 ohms if you have a bad module. Check for voltage at both. Both voltages should add up to 5v. But, they can't be equal. One should be say 2.35v and the other 2.65v. If they're equal, there's a short between the two. Sounds like you might have a bad ignition switch. Likely given…
Pins 6 and 14 go to the Front Control Module on this vehicle so you are not testing the network when you check the network's resistance at the DLC.
With the key in ACC position, some modules are powered off. I am not surprised to see not ideal bias voltage in that situation. If at KOEO the bus is operating normally, you will have to catch it while driving. I suggest the following scope settings: Timebase: 1 s/div, Number of Samples: 50MS, Trigger: Single, moved all the way to the right and down [9 sec, -9V]. Let it run and stop when the…
Did you see his first thread on this issue earlier?
Not really, I just wondered if you had seen the other thread on this car from earlier today.
Caught the bus issue in attached file. Not sure how to get decoder to work on it to decipher the culprit. Think I have an idea but not sure of best way to figure out. When I turn decoder on it says sample rate to slow.
Picoscope is not happy about 5MS/s rate, but it works just fine. Actually, you do not really need decoding for this one, because this does not look right anyway: diag.net/file/f5dui8bim…
Here is another sample with decoding on. diag.net/file/f7iagjigt… Not sure how to proceed from here. Is this a grounded bus? diag.net/file/f4imqp8f3…
It is a tough one – intermittent grounding of CAN High. Could be wiring rubbed through somewhere, but could be a bad module. It would be great luck if you could reproduce the issue while parked by shaking harnesses.
Good tip Dmitriy. This capture is from a 2010 F-150 with very intermittent no crank and many U codes. The scope is on the DLC pins 6-14 and sometimes when I banged on the under hood fuse box, I found this glitch. As it turned out, the problem was a bad solder connection in the cluster.
If a module is suspected, unplugged and reinstall one plug at a time at the star connector to isolate the module that may be causing the issue.
I cant see your Pico shots so hopefully you have termination ….A starting point U0001 would be scope readings CAN bus High/Low at DLC vs TIPM pins see if your way out somewhere ….. Doing what Mike says while hooked to TIPM …. Might as well just unhook the easy ones connectors see if it goes normal.
Would love to see a math channel of the differential voltage …between the two channels. cause that is what the modules actually use.
These are the good and the bad CAN C signals with the Math channels.
Finally got to the bottom of this one. Road testing until the bus misbehaved looked like this. diag.net/file/f6i41tnae… After a few unsuccessful trips I drove until the bus was way more bad then good and at that time I disconnected the abs module and the steering control module which allowed the vehicle to keep running but did not clean up the bus. I then cut the CAN bus wires…