Dlauth

2006 z06 and the rear defrost button will not light up.

I just replaced one rear hatch strut but I connected the wires and everything is tight.

Since I just got the car I'm not sure if the defrost was working before putting in the strut.

Ideas?

Dano523

The engine has to be running before the rear defrost will work.



Having said that, and the button will still not light up with the engine running, the System breaks down to three parts.

Part one is the HVAC control module that is the brains of the system. Its the part that will activate the system via the button push to make the button light up to begin with.

Next is the #40 relay in the engine fuse box and once the HVAC control module actives via the button push, it triggers that relay on so the battery can send 12 volts back to the window wiring grid.

The last part, The window wiring grid, which is 12 positive through one of the struts wires, through the window wiring grid, then through the other strut wiring to ground to cause the window grid protion to heat up.

So a easy test to weed out if the LED light is burnt out alone in your case, press the button, then either check relay #40 for power, or see if the back window is warming up. If no, then the HVAC control module is bad (most likely a cold solder joint) and you can either pull the module apart to re solder the boards to correct the cold solder joints, or replace the module with a new one.

As for anyone with the opposite problem (light will light up, but window will not get warn), then it's either relay number 40 that went south, or you have a bad connection down line of the relay instead ; being either one of the connectors at the top and bottom of the struts not connected/making a good contact, or one of the lead wires from the top of the strut to the window came un-soldered, and the wire just needs to be re-soldered to the window grid solder tab.

Dlauth

Can the car be in the accessory position to test this?

Dano523

NO, due to the amperage pull through the relay when the system is on, the HVAC control module will only allow the rear defrost to come on with the engine running (alternator turning to charge the system so you don't end up draining the battery).

Dlauth

That could be the issue standby until I can test with the engine running

Dlauth

I didnt have enough time to feel if the defrost was working but the LED does in fact come on when the car is running

Red08

My experience with the rear defroster is that it works EXTREMELY slow! Much slower than any other car I have had.

PatriotZ

Good to know info here....thanks

Dano523

If the button light is coming on, that is half the battle.

If the window is not getting warm, then check to make sure that the wire connectors (4) are hooked to both the top and bottom of the struts both sides.

With that out of the way, and then leave the car running, and on the top of the struts connectors, run a multimeter across the two wire to check for voltage (12 volts). If you get voltage, then the relay #40 in the engine fuse box is good. If you are not getting a 12V reading, then check again, but this time top drive strut connector to ground on the car. If you get a reading, then the problem is the left hand side lower strut wire is not connector to ground.

Now if you are getting a 12 volt reading across the two strut connector, but the window is not getting warm,turn the car off (will turn the system off), set the multimeter to ohm, and test the two top strut connectors again. You should be getting .5 ohms across the two struts.

If you are not getting a ohm reading, then pop the connectors off the struts and test again on just the wire connectors that are coming from the window. If you still get no reading, then one of the wires has come loose from the window grid taps, and it just needs to be re-soldered back on to the grid tab.