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BCM issues - ground points.

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12K views 10 replies 3 participants last post by  Gary Kline  
#1 · (Edited)
Hi,

2014 Cherokee Limited Diesel 4x4.

I am experiencing strange issues with BCM, i.e:

1. LIN1 bus issues. No reaction on 4WD/terrain rotary switch when inside rearview mirror is connected. When I remove the connector from the mirror (+12, gnd, microphone, LIN BUS) - the rotary switch works. This is the only 100% replicable issue. Changed the mirror with new one - same issue.
2. Occasional no start.
3. Intermittent no power to fuel pump.
4. Can-C occasional no communications (DTCs stored).

I need to check the ground points of BCM and related modules.

Anyone has an access to the documentation containing X-ray pictures of wiring harness ? Equivalent to that which was attached but for Cherokee.

Need to locate following ground points: G911A, G914A, G912A. Text descriptions in wiring harness diagrams are not precise enough.

Thanks in advance.
 

Attachments

#2 ·
  • G911A is right-front of center console (for mirror)

  • G914A is under the center console (SelecTerrain knob)

  • G912A is under-front of the center console (rain & humidity sensors)

Note, it's unusual for an ground point inside the car to not be intact (I guess unless you're looking at a one-off manufacturing defect where the screw backed itself out over time or the car was subject to flooding/water intrusion and there's hidden corrosion)

Unfortunately I don't have the ground point schematic equivalent of the Wrangler you showed. I only have it for the LIN, CANBUS and MS CAN networks like below. Sorry. :cry:

Image
 
#4 ·
  • G911A is right-front of center console (for mirror)

  • G914A is under the center console (SelecTerrain knob)

  • G912A is under-front of the center console (rain & humidity sensors)
Unfortunately I don't have the ground point schematic equivalent of the Wrangler you showed. I only have it for the LIN, CANBUS and MS CAN networks like below. Sorry. :cry:
Thanks for the reply. Much appreciated.
The dash was replaced. I suspect someone has forgotten about some ground nuts / connectors.
 
#3 ·
ps: If you remove the left and right kick panels (near the drivers and passenger seats) and then remove the center console (there are YouTube videos on how to do this), you can probably see most if not all the ground points mentioned (and more). Members of this forum often tap the ground point G912A which is accessible from the driver's kick panel for hooking up accessories like traffic cameras to switched ignition power at the 12v accessory outlet in the media hub.
 
#6 ·
Hi @tkacki ,

  • It appears the mirror, humidity sensor and SelecTerrain knob share the same LIN buss (network). You've already replaced the mirror. Does the humidity sensor plug into the mirror assembly or does it have an independent connector. If independent connector, try unplugging it in case it is defective and beaconing (transmitting) on the buss.

  • Also note on the schematic below, there are some "in-wiring-harness" connections for all these three systems that should be checked.

  • Last as a diagnostic step, if you unplug the humidity sensor, does the Mirror (auto dimming, etc.) and SelecTerrain knob both work at the same time?

Hope this helps.

Image


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Image
 
#7 ·
Hi @tkacki ,

  • It appears the mirror, humidity sensor and SelecTerrain knob share the same LIN buss (network). You've already replaced the mirror. Does the humidity sensor plug into the mirror assembly or does it have an independent connector. If independent connector, try unplugging it in case it is defective and beaconing (transmitting) on the buss.

  • Also note on the schematic below, there are some "in-wiring-harness" connections for all these three systems that should be checked.

  • Last as a diagnostic step, if you unplug the humidity sensor, does the Mirror (auto dimming, etc.) and SelecTerrain knob both work at the same time?

Hope this helps.
Hi,

Thanks for the reply and a lot of input.

Yes. I know this wiring diagram and checked all elements. I was disconnecting all the devices on this LIN leg one by one. I can read data using the OBD scanner from humidity sensor, rain sensor. Only in case when all is connected, bus goes down. So I have focused on supply / ground.
 
#10 ·
I have a 3016 Cherokee Limited. Can anyone tell me if the rear view mirror has a fuse in the power supply line? I tapped the wires to add a 12 v outlet and I think I fried something somewhere. The mirror has no power. My phone holder hangs from the mirror so I wanted an outlet to charge from. To rid the cord hanging in the middle of the seats. If there's no fuse, where do I go from here and what could I have killed.