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defroster light does not light on 2008

4K views 21 replies 6 participants last post by  AUTOSPARK 
#1 ·
defroster light does not light on 2008, nor does defroster work(rear). I cannot find a fuse? I am considering just replacing climate control unit. Is there a fuse? Does anyone have an electrical diagram of the back of the control unit as to where a person could test the control unit?
 
#4 ·
Is there a fuse??
Yeah, but not fuse #36. It's the one out on the engine bay that Pi_User5 mentioned.

Remo2110 said:
Does anyone have an electrical diagram of the back of the control unit as to where a person could test the control unit?
@wongpfh attached the circuit schematic, but what you really need is the AC control module connector pin out. He can't give you that though until you tell him what AC system your car is fitted with? Is it auto AC with the digital display, or is it manual AC with the three rotary controls?
 
#7 ·
Yeah, but not fuse #36. It's the one out on the engine bay that Pi_User5 mentioned.


@wongpfh attached the circuit schematic, but what you really need is the AC control module connector pin out. He can't give you that though until you tell him what AC system your car is fitted with? Is it auto AC with the digital display, or is it manual AC with the three rotary controls?
A/C diagrams attached.
 

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#8 ·
So I have even tried a different control module. Did not work. Which wires or how do I trace it to see if it works back to fuse?
or what do I do with the diagrams? I can use a multimeter. Do I test the rear defog pin on M22-2, number 23 with the ground Pin, and should get continuity? At a loss as to how to troubleshoot it. Any help would be nice.
 
#10 ·
At a loss as to how to troubleshoot it. Any help would be nice.
The very first thing I would do if I was troubleshooting the fault is check ALL the fuses(ignition on). Test them using a voltmeter or test light rather than removing them all from the fusebox and looking. That's a much quicker and easier way to test them.

The second thing I'd do is bypass the BCM and make sure the relay is able to switch on and supply power to the screen & tell tale light on the switch.

Referring to the defogger diagram you can see that the relay control wire enters the dashboard fusebox on terminal 8 of connector 'C' (blue wire). Locate that wire on the connector and back probe it using a pin (straightened out paper clip). With the connector still plugged into the fusebox, use a length of wire (or the ammeter in your multimeter) to connect the back probe pin to ground. When you ground the back probe you should hear the relay inside the fusebox click and the tell tale light on the switch should illuminate. If not, you'll need to check the relay power supply next, which is on terminal 2 of connector 'G' (heavy red wire).

BTW, a broken heater element/grid or a loose connection on the element power supply wiring shouldn't prevent the switch tell tale light from illuminating, according to the diagram at least.

Location of Fusebox Connector 'C'
 

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#11 ·
Autospark, So just to be clear is what u call a BCM, a Blower Control Module? I have been calling it a CCM, or Climate Control Module. Just to get the language straight. Second, If u want to bypass the BCM, why not check for power from back of BCM ,at plug M22-2 first. From what u say, I have no defogger diagram, nor a fuse box connector C diagram to show me the pin(terminal) numbers.
also u are talking of a relay inside of fuse box, that would be ate up, which would mean changing out fuse box C? Does not look very hard tho.
 
#13 ·
Remo2110 said:
I have no defogger diagram, nor a fuse box connector C diagram to show me the pin(terminal) numbers.
You do have the defogger diagram. It was kindly supplied by @wongpfh back in post #3 of the thread. I've re-attached it below, along with the pinout of fusebox connector 'C'. The pin numbers of the fusebox connectors are actually marked on the fusebox as are the connector identifier letters.

Remo2110 said:
just to be clear is what u call a BCM, a Blower Control Module?
No, BCM is the Body Control Module. It's actually the BCM that controls the rear defogger power supply relay, not the switch on the AC panel.

Remo2110 said:
I have been calling it a CCM, or Climate Control Module.
On the diagram that's called the A/C Control Module.

Remo2110 said:
If u want to bypass the BCM, why not check for power from back of BCM ,at plug M22-2 first.
Because, as stated above, the A/C Control Module (or CCM) doesn't actually control the defogger relay. You could test at the BCM connector if you wanted to but I think the fusebox is more accessible than the BCM.

Remo2110 said:
u are talking of a relay inside of fuse box, that would be ate up, which would mean changing out fuse box C? Does not look very hard tho.
You'd need to test the relay circuit to determine whether the problem is being caused by the relay inside the fusebox or not.
If the relay is faulty though, you don't necessarily need to replace the fusebox. You could, with a little guidance from myself, bypass the faulty relay inside the fusebox by adding an external one. It's maybe a little more work that simply swapping the complete fusebox but it will be significantly less expensive.




Only one row of pins is visible in the photo because of the camera angle.

 

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#14 ·
More questions

So included is the back of the fuse box. I tested to ground the bottom four wires on plug to right(ones on top in pic as is shown), smaller wires. I also tested the larger wires on plug to left(on bottom of pic as is shown). I recieved no click, and no tell tale light on switch whether i pushed it or not. By the way u can see the colors do not match with paragraph below. wire at pin 8 is yellow with orange stripe. pin 2 is gray with some type of stripe, just saying. Am I doing the right tests? Still working it. Appreciate the help.



The second thing I'd do is bypass the BCM and make sure the relay is able to switch on and supply power to the screen & tell tale light on the switch.

Referring to the defogger diagram you can see that the relay control wire enters the dashboard fusebox on terminal 8 of connector 'C' (blue wire). Locate that wire on the connector and back probe it using a pin (straightened out paper clip). With the connector still plugged into the fusebox, use a length of wire (or the ammeter in your multimeter) to connect the back probe pin to ground. When you ground the back probe you should hear the relay inside the fusebox click and the tell tale light on the switch should illuminate. If not, you'll need to check the relay power supply next, which is on terminal 2 of connector 'G' (heavy red wire).

BTW, a broken heater element/grid or a loose connection on the element power supply wiring shouldn't prevent the switch tell tale light from illuminating, according to the diagram at least.

Location of Fusebox Connector 'C'
[/QUOTE]
 

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#20 ·
Your test confirms that the fusebox is good, so you don't need to replace that.

To test the rest of the circuit you'll either need access to a decent scan tool, or the BCM on the car.
To access the BCM on your car you'll need to remove the center console. The BCM is under the console forward of the shifter...see below :

 

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#22 ·
There are three tests I would do at the BCM :

1. Test the input from the alternator. The alternator sends a signal to the BCM once the engine is running and the alternator starts to charge the battery. The rear defogger is a heavy electrical consumer and the BCM wont switch it on if the alternator signal isn't present. The green wire on connector 'A', position 3 should have 12~14V when the engine is running.

2. Test the input from the defogger switch on the heater control panel. The brown wire on connector 'B', position 18 should be pulled to ground when the defogger switch is pressed.

3. Test the relay control output. The blue wire on connector 'C', position 3 should be pulled to ground when the defogger is switched on. This is the same wire that you grounded at the fusebox.

I've attached the pinout of the three BCM connectors below. You need to test by back probing the connectors while they are plugged into the BCM. The diagram shows the connectors viewed from the wiring side. To test the alternator signal connect your black voltmeter lead to a good ground and probe the green wire with the meter's red lead. To test the ground input from the switch and the ground output to the relay, connect the meter's red lead to a good 12V power supply and probe the wires with the black lead.

 

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