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post #1 of 7 (permalink) Old 05-25-2019, 03:39 PM Thread Starter
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Help with wiring diagrams and DTC lookup table

I bought a 2015 GT last week and have been digging through the car to clean up a few issues I discovered - mostly electrical. The AFS unit for the headlights appears to be defeated - AFS is unplugged and a small bundle of wires are spliced together nearby (looped CANBUS circuit?).

I'm having some trouble deciphering the wiring diagrams - specifically the DTC troubleshooting tables with their numbered connectors they tell you to inspect, but don't tell you where those connectors can be found, look like, or the complete pinouts for the connectors. Am I missing something, maybe my manual is incomplete? I downloaded it from a link I found here. The interactive wiring maps are nice, but the connectors aren't cross referenced back to the diagrams, so they aren't very useful.

I'm getting a U0155 code, so the DTC troubleshooting says to inspect C-34 and C-35 if anyone has info on where they are on the car.
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post #2 of 7 (permalink) Old 05-25-2019, 04:25 PM Thread Starter
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Here's a pic of the questionable decision-making skills of the previous owner that I'm trying to sort out. This is under the dash behind the steering wheel, and I think this bundle may be the one that originally went to the AFS unit.

If anyone with a GT can post a few pics of their virgin wiring under the dash, that would be helpful.
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post #3 of 7 (permalink) Old 05-26-2019, 03:52 PM Thread Starter
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New item to add to my electrical woes: I upgraded the trunk light to an LED and noticed it just stays on all the time, it doesn't even turn off after the 30 minutes that's supposed to be the failsafe. The manual shows the RBCM switches this directly, yet the dash shows the trunk close/open accurately...so I don't know what to make of that.

Wish I had an M-MDS...
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post #4 of 7 (permalink) Old 05-26-2019, 04:23 PM
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In theory if its actually fully switched it should go off regardless of what load is present; however, I have seen various people having issues with non-headlight LEDs not turning off with 3rd Gen 6s, so for whatever reason it seems that the potential at the blub doesn't truly drop to 0, even when the device is supposed to be off. There's enough of a difference to keep some LEDs powered, especially the smaller ones.

Something related to the switching system working correctly must be dependant on the each load being nominal for a halogen. I haven't looked into the schematics at all myself (they're quite terrible in some locations to be frank) but I just know this is a common issue.
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post #5 of 7 (permalink) Old 05-26-2019, 06:31 PM
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Quote:
Originally Posted by fivil View Post
New item to add to my electrical woes: I upgraded the trunk light to an LED and noticed it just stays on all the time, it doesn't even turn off after the 30 minutes that's supposed to be the failsafe. The manual shows the RBCM switches this directly, yet the dash shows the trunk close/open accurately...so I don't know what to make of that.

Wish I had an M-MDS...
There's a good chance you fried the rear bcm with the trunk led, there is a flaw with the rear BCM where that fries before the fuse, several people have reported that here already when they tried swapping out for LEDs. I would try swapping the LED back to the stock bulb

as for the wiring diagram, here is the service manual for the car:
2014 - Mazda6 Workshop Manual
The wiring diagrams require flash, which Google Chrome does come with preinstalled. When you open up a wiring diagram, you may have to click in the center to allow chrome to run flash
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post #6 of 7 (permalink) Old 05-27-2019, 02:04 PM Thread Starter
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Quote:
Originally Posted by oblivioncth View Post
In theory if its actually fully switched it should go off regardless of what load is present; however, I have seen various people having issues with non-headlight LEDs not turning off with 3rd Gen 6s, so for whatever reason it seems that the potential at the blub doesn't truly drop to 0, even when the device is supposed to be off. There's enough of a difference to keep some LEDs powered, especially the smaller ones.

Something related to the switching system working correctly must be dependant on the each load being nominal for a halogen. I haven't looked into the schematics at all myself (they're quite terrible in some locations to be frank) but I just know this is a common issue.
I put the incandescent back in and it still stayed on, I think RickyBobby nailed it this time.

Quote:
Originally Posted by RickyBobby View Post
There's a good chance you fried the rear bcm with the trunk led, there is a flaw with the rear BCM where that fries before the fuse, several people have reported that here already when they tried swapping out for LEDs. I would try swapping the LED back to the stock bulb

as for the wiring diagram, here is the service manual for the car:
2014 - Mazda6 Workshop Manual
The wiring diagrams require flash, which Google Chrome does come with preinstalled. When you open up a wiring diagram, you may have to click in the center to allow chrome to run flash
Well son of a b. Looks like I shot myself in the foot on this one. I'm going to assume it's a load-limited circuit because a diode load vs a resistive load shouldn't matter. I tested the circuit with about 20W worth of LED strip before settling on about 4-5W, and I'm going to assume that anything over say 10W would probably kill the switch (maybe a tiny mosfet?) in the RBCM. Now to find out if anyone has opened one up to see what failed...

Yeah, that's the manual I have, I'm just a bit displeased with the organization and layout of the info.
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post #7 of 7 (permalink) Old 05-27-2019, 04:44 PM
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Ouch, annoying flaw.
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