CAN C Bus Where is the other 120 Resistor

Ronald Technical Support Specialist British Columbia Posted   Latest  
Resolved
Driveability
Network Communications
2006 Jeep Grand Cherokee Laredo 3.7L (K) 5-spd (W5A580) — 1J4GR48K16C334900
U0001 — High Speed CAN Communication Bus
U0002 — High Speed CAN Communication Bus Performance
Intermittent Loss Of High Speed Can Bus

I am trying to find the culprit in High Speed CAN Bus. Bus Resistance is 120 Ohm and that resistance is in the PCM. Can anyone tell me what module is supposed to have the other 120 Ohm resistor. Steering column Module or Gear Shift Module or TIPM (Front Control Module) or ….

Thanks for any help.

0
Helpful
Jeremy Technical Support Specialist
Minnesota
Jeremy
 

It will be in the front control module

+5
Ð Awarded
Thanks
Agree
Bob Technician
Massachusetts
Bob
 

Damn, beat me to it.

+2
Ð Awarded
Funny
Geoff Diagnostician
Hawaii
Geoff
 

Imagine that! Right there in the SI. Sigh…. ;-)

+2
Ð Awarded
Ronald Technical Support Specialist
British Columbia
Ronald
 

Yes. I was impatiently looking. I blame it on old age.

0
Ð Awarded
Dan Owner/Technician
Texas
Dan
 

… It gets WORSE ! … Dan H.

0
Ð Awarded
Bob Technician
Massachusetts
Bob
 

I did a little searching and turned up this. I highlighted the important part in paragraph 3 OPERATION The Controller Area Network (CAN) data bus allows all electronic modules or nodes connected to the bus to share information with each other. Regardless of whether a message originates from a module on the lower speed CAN-B bus or on the higher speed CAN-C or CAN-D bus, the message structure…

+5
Ð Awarded
Helpful
Thanks
Kerry Mobile Technician
Ohio
Kerry
   

Ronald, Jeremy and Bob have supplied you with all the information you need about the system. May I ask where you are taking your measurements, though? Are you taking it at pin 6 and 14 of the data link connector? Or are you taking a measurement with the FCM gateway unplugged and measuring downstream from the FCM (pins 8&9)? If you are measuring downstream with the FCM disconnected then…

+1
Ð Awarded
Ronald Technical Support Specialist
British Columbia
Ronald
 

Thanks for info. Yes I was measuring at pin 8 and 9 on FCM unplugged and was getting 120 ohm and then when I unplugged PCM I was getting infinite resistance but when I plugged FCM back in and measured from PCM I was still getting an infinite resistance and that was what made me decide to ask about where the other 120 ohm was. When I was doing this I still had the battery connected so I…

0
Ð Awarded
Stephen Technician
Tennessee
Stephen
 

Is the fault, while driving, the same as the fault shown in the ACCy mode? Is the bias shift in ACCy always there? Can you post a picture of the CAN C bus layout?

0
Ð Awarded
Ronald Technical Support Specialist
British Columbia
Ronald
 

I don't think I get faults in the ACCy mode. I believe there are no faults until the bus intermittently cuts out while driving. I should really check if it faults in ACCy mode though. The bias shift is always there in ACCy mode. Here is the CAN C layout. diag​.​net/file/f4duty5ix… ​

0
Ð Awarded
Stephen Technician
Tennessee
Stephen
 

The bias shift in ACCy is likely not a fault. It is a strategy of the bus being turned off. I would disregard it and get a capture of when the fault is occurring. Comparing the layout of the bus connections to the NO Comm complaints didn’t give a direction due to the ring type layout. Although S104 and S105 do give convenient access to isolate the modules except for the SCM and shift lever…

+1
Ð Awarded
Thanks
Ronald Technical Support Specialist
British Columbia
Ronald
 

No codes set in ACCy mode. Thanks I will disregard the bias shift and try and record failure while driving again. Out of shop until Monday but will try again then.

0
Ð Awarded
Ronald Technical Support Specialist
British Columbia
Ronald Resolution
 

120 ohm resistors are in PCM and TIPM (FCM) as many told me. Ultimately road testing until the bus started to act up eventually led me to a problem with the CAN bus in the PCM. My CAN Diagnostics post has more info on my diagnostic endeavors. Thanks for all your help.

0
Resolution Ð Awarded