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Discussion Starter #21
Thanks for reply and your input greatly appreciated!
As a matter of fact I did replace my abs actuator electronic control unit with a part number I mentioned earlier. I also verified applicability with Nissan. Everything works and is online with with CANbus. As you mentioned earlier, this brake warning light is a discrete signal from two switches (handbrake and low fluid level switch) and flow logic from UMCU (integral part of unified meter control unit) and also a pass-thru signal on the ABS actuator and electronic control unit which I have rang through for continuity and ground to low level switch as per BRC PDF.
This really leaves me with UMCU...
What are your thoughts? Thanks again.
I would hate to think a short-circuit in UMCU...
 

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09 Altima 3.5SE 6MT Sedan
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If you unplug the ABS actuator and the brake light goes out...then you know for sure where it's coming from. As always, I would recommend disconnecting the battery first, then unplugging harness(es) from the ABS controller, then reconnect the battery and turn on the ignition...ABS light should come on, Brake light should go out.
 

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Discussion Starter #23
From what I have read in BRC PDF (abs and ebd function) see attached, brake warning light will come on if abs or any artificial safety layer layer within that system is degraded or taken off-line due to electrical fault to engage Fail-fail safe function thus having regular brakes only.
I do not believe vdc module has anything to do with brake warning light even though a discrete is passed thru abs elec Ctrl unit. However, I will follow you recommendation to troubleshoot this way.
Screenshot_20200713-130440_1.jpg
 

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09 Altima 3.5SE 6MT Sedan
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If the VDC is a discrete module, disconnect that. My presumption was it was integral to the ABS controller...I may be wrong!
 

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Discussion Starter #25
You are correct, vdc is part of abs actuator electronic control but no without other inputs especially from yaw sensor.
But what I mean is the brake warning light actuation signal does not get processed as it is simply a discrete from brake low fluid handbrake and charging circuit, where as abs wss signal as an example does.
 

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09 Altima 3.5SE 6MT Sedan
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You are correct, vdc is part of abs actuator electronic control but no without other inputs especially from yaw sensor.
But what I mean is the brake warning light actuation signal does not get processed as it is simply a discrete from brake low fluid handbrake and charging circuit, where as abs wss signal as an example does.
I think I agree. Regardless if you disconnect the harness from the ABS control unit, then the 4th input for that light also gets disconnected...and if the light goes out...you have narrowed it down...from there you can look behind the ABS control...such as the yaw sensor.

The ABS control might throw an ABS code because of the light...and that might help you narrow it further.
 

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Discussion Starter #27
I'm going to ring through a harness pin 17 of UMCU to F1 of the generator as per DI-47 circuit diagram.
Thank you for your thought on the subject. I feel I'm very close in solving this issue. I'll keep you advised. Cheers
 

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Discussion Starter #28
Update: UMCU was the culprit! Diode logic was the issue. I'm attaching diagram snippet. All is good now. No more brake warning light. It does come on with handbrake actuation as required. Wish to thank you very much as you were the only one who answered the call. Cheers
_20200714_133301.JPG
 

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Discussion Starter #29
I had a hunch it was UMCU given the condition of fuel needle gauge. UMCU had an internal short and burned the diode logic and in result messed the fuel gauge and turned on inextinguishable brake warning light.
 

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09 Altima 3.5SE 6MT Sedan
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Ok...hope you didn't just cut the wire :) I don't think the diode logic failed, as it can really only fail in two ways...open circuit which could never illuminate the Brake light, or a straight short (much more uncommon for diodes) which would still only illuminate the light if the ABS signal is pulled to ground indicating a fault. The only reason the diode is there is to prevent a switch such as the handbrake or fluid level from 'shorting out' the driver output from the ABS controller.
 
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