Wiring diagram explain please

[01 monte fan]

I am trying to figure out the issue with my rear defrost.  I have no voltage back at the grid or the plug to the defrost/antenna module. I press the button and the light turns on but I don't hear a click for the relay.  I have tested for voltage at the relay and have 12v on the 30 pin but no voltage on any other pin when the button is pushed on.

I am wondering if it's possibly the hvac control panel. I don't know how power is routed into the relay to know if it's the panel or bcm that supplies the power for the relay. 

I sure hope someone can direct me on where to look next. Thanks for any guidance here!!

Edited March 17 by 01 monte fan

[GnatGoSplat]

You should be seeing +12V when measuring across pins #85 and #86 on the relay socket (N3 and L2 in the diagram).  L2 should be grounded and N3 should be +12V with the ignition turned on.  If you don't see +12V on N3, try checking with positive lead of your voltmeter in N3 and negative lead on any grounded metal screw.

 

[01 monte fan]

Ok, so I have tested voltage previously with relay removed. I have 12v on L3, but I ground out the negative terminal of my volt meter and have tested n3/L2 seperate. I have .5v on n3, 0v on L2 with button on.

I will try a jumper for n3/L2 and see if any voltage is there and report back. 

I was thinking that I should have 12v coming from the defrost button (L2) and not the bcm (n3)...

Edited yesterday at 12:42 AM by 01 monte fan

[GnatGoSplat]

Connect your meter positive lead to the 12V on L3 and negative lead to the relay socket L2.  With button on, do you see +12V?

L2 should short to ground when the button is on.  On the diagram, the "Rear Defog Relay Control" is an electronic switch and that tapered 3-line symbol is ground.

[01 monte fan]

Yes I have 12v between L2 & L3 with button on. But I also have 12v with the button off....

There's one thing I forgot to say, but the temp control panel was swapped out at one point from another monte... I didn't have my window terminal fixed before the change (its fixed now)... don't know what yr it was but they were identical at least on hookups. Could it be possible that the panel is different from the original that would cause this?

Edited 22 hours ago by 01 monte fan

[GnatGoSplat]

Interesting that it's 12V with the button on or off.  It may be a transistorized output with its "off" state floating, so we won't be able to see the voltage change without a small load across it.  With the relay out, can you use jumper wires to connect L2 and L3 to the relay's #85 and #86 pins (the coil) and see if it clicks on and off with the button on the HVAC panel?  It's possible the panel is different, but if it looks identical and has an identical connector, I doubt it would be different.

[01 monte fan]

Ya I can feel and hear the relay switching with the button on and off. 

[GnatGoSplat]

Ah, so the relay is good and the HVAC panel is good.  Looks like the BCM is bad or there's a bad connection between the ORN wire going from BCM to N3.  Now I would disconnect the BCM and check for continuity between B8 on connector C2 of the BCM and N3 pin on the socket of the relay.

 

[01 monte fan]

Sounds good,  I will check that this weekend and see what I get. So I just want to make sure I am understanding all this... but am I to understand that the 12v should be coming from the bcm to the relay and over to the switch to close the circuit? On the bcm terminal there's only .5v

[GnatGoSplat]

1 minute ago, 01 monte fan said:

Sounds good,  I will check that this weekend and see what I get. So I just want to make sure I am understanding all this... but am I to understand that the 12v should be coming from the bcm to the relay and over to the switch to close the circuit? On the bcm terminal there's only .5v

Yep, there should be +12V from the BCM on relay pin N3, I'm thinking when the ignition is on.  The panel then grounds L2 when rear defog is on, which should close the relay.  Looks like the +12V is missing.

The BCM supplies the positive to the relay coil while the panel supplies the negative.

The BCM also powers other things, according to the little note "Starting and Charging Schematics in Engine Electrical".  I wonder if any of those things are not working?

[01 monte fan]

Honestly I have no other issues with the car. Once in a while my oil psi gauge won’t read but if I turn the key off and back on it resumes functioning normal. The only other problem I have is with a/c pump not turning off and staying engaged continuously. That I figured is probably a pressure switch issue. I replaced the pressure switch but I am waiting till it gets warmer to charge the freon back up.

When I pull the bcm down I will check for voltage out of the orange wire and see if or where it's loosing power to the relay fuse block.

Are there any images of how it's routed and loomed from the bcm to the relay fuse block on the passenger side?

Edited 3 hours ago by 01 monte fan