Chrysler CAN bus B problem

Roberto Diagnostician Fremont, California Posted   Latest   Edited  
Trained By Techs
2005 Jeep Grand Cherokee Limited 5.7L (2) 5-spd (545RFE)—1J4HR58275C617391
Cluster Goes Death Once In A While

This jeep 2005 grand Cherokee uses CAN B network to communicate with a lot of modules, CAN B has a different bias voltage that the regular CAN, CAN B + has a range of voltage of about .5 volts when alive or talking CAN B - has a range of about 4.5 volts when alive, now, I have this car and Am getting a lot of codes related to the (-) line U0024 CAN B bus circuit open, when testing the network for voltage it fluctuates a lot, it goes from 3.8 volts to over 5 volts on the (-) bus line and on the (+) line it goes from .2 to .9 volts which is probably normal (Am still testing how this network works), there were two modules that always had a code, it was the heated seat control module and the parking control modules I disconnect those two and some other modules DDM, PDM and Am still getting codes for my minus CAN bus (U0024), my question is if you guys have more experience on this network, if my body control module is still saying that there is a problem with my B- bus line it is because maybe my body control module is the one to blame? how you guys test for a waveform signature? I scope the signal and Am going to upload a video of the signal right after so you can look at it and see what you think. 

Another think to add is that the network is no shorted to ground, with the scope I can see both lines acting like a mirror to each other but maybe too noisy?

Caleb Diagnostician
Mishawaka, Indiana
Caleb Default

Hey Robert yes. This is normal Body CAN amplitude for Chrysler. However I would agree that the packets look more like sine waves than square waves. This is usually indicitive of a high resistance issue somewhere as your codes would suggest. But before getting into waveform analysis I have a couple questions. #1 What is the customer complaint? What are you trying to fix? #2 Have you established…

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default

I apologize just now saw the cluster goes dead intermittently. Which leads me to a couple more questions. #1 Are the waveforms you posted with the cluster dead or not? #2 Have you duplicated the cluster going dead?

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Roberto Diagnostician
Fremont, California
Roberto Default

Hey Caleb, actually I haven't seen the cluster doing that, all the time that I took some samples it has never failed and neither the other complaints that my customer had, he says that the cluster goes off (gauges and everything) and that the parking warning is active even if he is not close to anything, but not luck duplicating the problem so far.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default

Pull the cluster part way out, and gently rock/tweak/twist the connector up and down, see if the problem duplicates.

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Stephen Technician
Gallatin, Tennessee
Stephen Default

carlogic​.​org/bg/data/MB%20C…​.​pdf This article explains CAN B voltages and has screenshots. It’s very different than yours so, I’m thinnking that there is a line in trouble just as the BCM claims. I guess it could BE the BCM. I would test the modules individually. Which would be easiest by clipping the CAN lines to isolate them from the rest and test the module and…

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default

Hi Roberto I have a 2006 GC 5.7 here, its been here for some time with the C19 lockdown, one of the customers complaints is occasional dropping out of the instrument panel, he also say's that the headlights go off as well (pulls over switches off and restarts all is well) I believe in all the time its been here I saw the instrument panel flicker once. Will keep an eye on your progress.

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