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2005 BMW 335i No Comm Through DLC

  • Donut
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16 Sep 2020 10:24 #43149 by Donut
2005 BMW 335i No Comm Through DLC was created by Donut
As the title says I've got an '07 335i in my bay that was towed in after a customer replaced their battery and after nothing worked, no crank and no dash lights, and swears they didn't jump anything off backwards. Not for me to judge, after servicing used car lot vehicles for years I've seen plenty dumber things happen. Spent a while on it and it indeed didn't have 'ignition on' power but it did power up a few things inside, one of which was the network so I was actually able to communicate and do a full system scan. After doing some other tests eventually lost all ability to communicate with the vehicle but managed to diagnose a faulty Car Access System module as the power issue. Got the new one in and problem fixed except for the communication issues.

The biggest challenge here is I have a mismatch between what is on this vehicles DLC port and what my schematic is showing. Mitchell shows the junction box as being the gateway for vehicle comms through the DLC ports pin 7, but on the vehicle it's an empty hole. Instead I have what looks like a weak CAN H signal on 14. So I'm kind of at a loss as far as this one goes without wasting a bunch of time with nothing to show for it.

We only have access to Mitchell and all the diagrams on it I could find are all the same. Does anyone have any others that show any communication lines that go to pin 14? Or maybe run across an issue similar to this?

"Don't ever say 'easy' until the check clears."

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  • Hardtopdr2
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16 Sep 2020 11:56 #43151 by Hardtopdr2
Replied by Hardtopdr2 on topic 2005 BMW 335i No Comm Through DLC
What are the codes? Are the comm issues current or in history? Has the battery relearn procedure been done?

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  • Donut
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16 Sep 2020 17:23 #43153 by Donut
Replied by Donut on topic 2005 BMW 335i No Comm Through DLC
Found the issue after taking a break from it, but to answer your questions the issue that was present was I was losing total communication to everything. When it first came in I did register the battery and after I scanned it every module did have all the typical low voltage codes associated with a dead battery.

The underlying problem turned out to be a case of 'customer attempted prior repair'. My favorite! It turns out there are pins for H and L CAN on this connector, I didn't see a pin in the #6 spot because for whatever reason the customer removed the factory pin (which is a copper color) and replaced it with a regular (silver colored) pin that doesn't even fit into the DLC port that was nearly impossible to see unless you focus. I guess I was barely touching the pin before and pushed it out the last time I scanned it. Got a couple pictures of it, they used a few different wires for a few foot run and I have absolutely no idea why.

"Don't ever say 'easy' until the check clears."
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