Top warning light on DTC B1777

High_Octane

Just recently I noticed my top warning light to be permanently on, but I can still operate the top as per normal with no issues.

Checked with a reader and saw there is an error code B1777 which says "Rear window defogger output signal circuit is short to power."

Been trying to trace the wires but don't see any chafing. Studied both Roof and Defogger manuals but doesn't make sense...
I already tried removing the 2 20A fuses but I still get an error.



Any ideas?

OldGuyFla

Does the defogger work?

I checked out the manual & it looks like to me a good starting point would be at connector B311. But the manual says that connector isn't shown on the cable layout. I'll take a look at my car & see if I can find B311.

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High_Octane

Defogger for the rear window does not work. This DTC B1777 prevents that from happening. I can still turn on the defogger switch though.
What I am guessing is that pins 104 and 111 are getting power, which should not be the case since they are outputs that supply power to the defogger.
I already took out the two 20A fuses so pins 48 and 49 which are input pins, should not have any power going to it.

And how do you work in the roof compartment without the lid closing after a few mins? Disconnect the battery after opening the lid?

OldGuyFla

I had never left the lid open for any long time, so I went out this morning & let it stay open for an hour & it is still open. I don't know why it would close on its own.

Looking at my car I see a connector right at the lower side of the window on the right side. It plugs into the defogger. Have you tried seeing if that connector has voltage going to it?

Have you tried ohming out the actual filaments in the window to see if they are shorted?

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High_Octane

My lid closes after about 5mins if left opened with the ignition turned off. Apparently it is some safety feature.

I tested out with a volt meter at each end of the rear window and strangely, I see 4.9V even though I did not turn on the rear window defogger.
I think I really do have a short going on.

I am going to be busy tracing wires this weekend...

SouthArk370Z

I have next to no experience with convertible tops (zero with 370Z verts) but I spent several decades doing industrial instrument and electrical work. In my experience, a signal line is low-current and, in this case, would be used to energize a relay that sends power to the heating element. My guess is that the SOFT TOP CONTROL UNIT contains the relay(s) and your problem is with the circuit that tells the STCU to energize the relay. But that's just a guess.

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High_Octane

I don't think that is how it works for the roadsters.
Pressing the defog button does energize a relay and that sends power to the heated mirrors. For the rear window, the power will pass through two 20A fuses before going to the Soft Top Control Module.
The Soft Top Control Module will check the state of the top (open or close) before sending power to the rear window.
This is after studying the wiring diagram that I manage to get.

High_Octane

Alright, here is an update.

After much checking, I confirmed my defogger is dead. Likely some of the lines are broken (can't be seen visually though). I don't use the defogger though, so my first solution was to disconnect the wires to the rear window.
This does not work! It seems the Soft Top Control Module will check for continuity.
Ended up wiring a bypass wire with a resistor and that solved my problem.

So to all roadsters, if your rear defogger decides to die on you, it will keep your soft top light lit.

OldGuyFla

Nice little fix, way to go.

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Bummer

Thanks for the info. Filed for future reference.

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Steve

ZETIRED

I came across your thread, and I realize it's fairly old, but I have a similar problem with my 2010 Z roadster top. The Top Icon is always on, but the top works fine. The dealer Scanned for codes and they found the code B1777. This code translates to a short in the rear window defrost wiring. I took the car home to see if I can fix the problem. Upon very close scrutiny I found a chafed wire on the drivers side taped to a hinge. I was able to repair the wire however the Top Icon is still on. I saw you wiring schematic, and I noticed that the are 2 20 amp fuses listed and I want to check them to see if they had opened due to the short. However I have no idea where they are physically located. I checked the fuse box next to the battery, nothing. I can't find them. Can anyone tell me where these two fuses are actually located. Thank you all.
You can also reach me at r.caliebe@gmail.com. Any help would be appreciated.

SouthArk370Z

According to the diagram, they are in the same fuse block that houses the Rear Window Defogger Relay and the 10A fuse that powers the door mirror defoggers. Should be able to search the FSM for "Rear Window Defogger Relay" to get a location.

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10MPlayer

I just had to replace a couple of hydraulic lines and fix a broken wire a while back. I did it old school and propped it open with a stick.

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6SpeedZ

I could really use your help ... I've read through all of the pasts posts & do not see the issue that I am having.

Recently had my top replaced by a "professional" in NH before moving back to the Treasure Coast of FL. There are two issues that the shops convertible specialist & Nissan master techs around here cannot seem to figues out & fix.

1, The wire that attaches to the defrost is no longer attached to the glass (the "pro" in NH said that I brought him the top that way).

2, Now (thanks to the local shops) the button to open and close the top actually works. The top will open all the way and then BEEP once the top is fully open. HOWEVER, when I go to close the top the roof closes all the way and locks in the back, but does not BEEP and the second you let go of the button it pops back up on the front (windshield).

*When the master techs hook up the Nissan Scanner to the car there are no codes whatsoever. They are at a loss for how to figure this out & fix it ... Please Help!

Thank you!

Defib

Any idea what resistor is needed with the bypass? I'm having the same issue as High_Octane?

Update: I disconnected both wires from the defroster and installed a 24AWG (1 of 2 speaker wire) and "Voila!" the softtop light disappeared. For now ....