CAN2 HI Waveform Interpretation
We've got a 2015 F-150 5L with about half of HS CAN2 off line. Attached is the waveform captured just before the occupant classification module. Are these lines shorted together or is it something else? Thanks for any insight.
I would suggest get rid of the trigger, and what sample rate are you using and are you certain of a good scope ground? Here is a screen shot of one of the pages for others to view.
Scope ground is good, double and triple checked. Trigger made no difference.
I would start with monitoring the HS2 while unplugging some of the suspect modules on that network. Common areas would be OCSM and wiring under seat, PSCM and connector. TCCM in right kick panel for water intrusion, wiring at and near CCM in front bumper. I don't think they are shorted together, but on this page near the end, they certainly look to be. Also check resistance at pins #3 & 11…
Thanks for putting up the screen shot. This Ipad won’t open pico files.
Can you post an HS2 wiring diagram and tell us who is online and who is offline please??
OK thanks sir. What is the resistance at pins 3 and 11 with battery disconnected?
Should be 60 ohms? Looks like terminating resistors for HS2 are in SCCM and Gateway. Did you test across DLC pins 3 & 11?
OK thanks. You need to find the open circuit. If you really have 120 ohms with all modules connected and battery disconnected then that is the issue. No need for scope. Simply find the open circuit.
Hi. David, Just want to follow along and learn, would like to ask a couple questions. Did you happen to get a capture of the resting voltage on the CAN ? Was this the same wave form you had at DLC with OCCM plugged in ? Did you measure for the terminating resistors in CAN circuit? Thank you!
If the lines were shorted together then, both lines would have the same voltages, at the same time. I would be an exact copy of the other, as if it was the same wire which, is what a short does. It makes two wires become one. The traces, both return to their reference voltage(2.5V) so, shorted to ground or shorted to battery is not possible either.
With the SCCM disconnected, our waveform returns to a more normal pattern. In addition, we've measured CAN wires at ABS and OCM to various spots in the network and all appears OK. Curious thing, with the SCCM unplugged there's still no communication with Air Bag and ABS modules?
If you have 120 OHMS resistance I would not worry about the wave form until you figure out why you don't have 60 OHMS. The SCCM is a terminating module. With battery disconnected unplug connector at SCCM. Test resistance on CAN lines you should see 120 OHMS resistance back to the other terminating module (Gateway module.) If the wirng to the Gateway Module is good check resistance at SCCM again…
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Thanks for everyone's replies. Best advice I got was to put the scope away and figure out whey the HS2 Network had 120 ohms. Found an open behind the BCM at the passenger side kick panel. Repaired and all returned to normal. Again, thanks for your time and thoughtful responses.