Question about Chevrolet TrailBlazer

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My 2004 6cfl. Trailblazer rear window defroster is not working. The wires appear to be making a good contact. The outside mirrors defrost ok using the same switch as the test window defroster. Is there s separate fuse for the year window defroster? Is there a module that runs the rear window defroster? Where would that be located? What else could be the cause of the rear window unit not working? Think you for your help.

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  • Chevrolet Master
  • 12,461 Answers

There is a module that controls the rear window defogger grid . LGM/ EGM Liftgate or endgate module .Receive's message on class 2 serial data network from the HVAC control module to turn it on when button pressed . Fuse # 3 30 amp located in the rear fuse box . Do you know where the rear fuse box is ?
Rear Window Defogger Description and Operation
Rear Window Defogger System Components
The rear window defogger system consist of the following components:
• HVAC control module
• Liftgate module (LGM)/endgate module (EGM)
• Rear window defogger grid
Rear Window Defogger Operation (With LGM)
Battery positive voltage is supplied through the LGM 2 fuse to the LGM for the rear window defogger system. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator, and sends a class 2 message to the LGM to enable the rear window defogger. The LGM enables the rear window defogger by allowing battery positive voltage to the rear window defogger.
When the rear window defogger switch is pressed for the first time, the defogger cycle lasts 10 minutes. Further operation results in 10 minute defogger cycles.
Rear Window Defogger Operation (With EGM)
Battery positive voltage is supplied through the EGM 2 fuse to the EGM for the rear window defogger system. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator, and sends a class 2 message to the EGM to enable the rear window defogger. The EGM enables the rear window defogger by allowing battery positive voltage to the rear window defogger.
The following conditions must be met for rear window defogger to operate:
• The end gate glass position is not below the index position.
• The window express down movement is not requested.
• The window down movement is not requested.
If the end-gate glass is not fully closed, the DIC displays "Tailgate Glass Down" when the rear defogger operation is attempted.
When the rear window defogger switch is pressed for the first time, the defogger cycle lasts 10 minutes. Further operation results in 10 minute defogger cycles.

Fuse Block - Rear
Beneath the left rear seat

Posted on Jul 13, 2017

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SOURCE: My 2004 Dodge Ram 2500 SLT Diesel vent control

Hi!!

IT SEEMS LIKE YOU HAVE A SHORT IN THE HEATING GRID, EITHER THE MIRRORS OR THE BACK WINDOW.

READ THE FOLLOWING INFO. AND PERFORM THE TESTS TO PINPOINT THE FAULT.

OUTSIDE MIRROR HEATING GRID
Vehicles equipped with the optional heated mirror
system have an electric heating grid located behind
the mirror glass of each outside rear view mirror.
The heated mirrors are controlled by the rear window
defogger switch. Electrical current is directed to
the heating grid inside the mirror only when the rear
window defogger switch is in the On position.
The heating grid behind each outside mirror glass
cannot be repaired and, if faulty or damaged, the
entire power mirror unit must be replaced.

DEFOGGER SWITCH
The rear window defogger switch is integral to the
rear window switch pod, which includes the rear
wiper and washer switches. The rear window switch
pod is installed in the instrument panel lower bezel,
which is located near the center of the lower instrument
panel, below the heater and air conditioner controls.
The rear window switch pod also contains the rear
window defogger logic and timer circuitry, an amber
defogger indicator lamp, the rear window defogger
relay, and two switch illumination lamps. The indicator
and illumination lamps in the switch pod use
incandescent bulbs, which can be serviced.

The momentary-type rear window defogger switch
provides a hard wired ground signal to the rear window
defogger logic and timer circuitry, each time it is
depressed. The rear window defogger timer and logic
circuitry responds by energizing or de-energizing the
rear window defogger relay and the amber defogger
indicator lamp, which lights to indicate when the
defogger system is turned On. Energizing the rear
window defogger relay provides electrical current to
the rear window defogger grid.

The rear window switch pod cannot be repaired. If
any function of the switch pod except lighting is
faulty or damaged, the entire switch pod must be
replaced.

Turn the ignition switch to the On position. Set
the defogger switch in the On position. The rear window
defogger operation can be checked by feeling the
rear window or outside rear view mirror glass. A distinct
difference in temperature between the grid lines
and the adjacent clear glass or the mirror glass can
be detected within three to four minutes of operation.

Using a 12-volt DC voltmeter, contact the rear
glass heating grid terminal A (right side) with the
negative lead, and terminal B (left side) with the positive
lead (Fig. 1). The voltmeter should read battery
voltage.

The above checks will confirm system operation.
Illumination of the defogger switch indicator lamp
means that there is electrical current available at the
output of the rear window defogger logic and timer
circuitry, but does not confirm that the electrical current
is reaching the rear glass heating grid lines.

If the defogger system does not operate, the problem
should be isolated in the following manner:

(1) Confirm that the ignition switch is in the On
position.
(2) Ensure that the rear glass heating grid feed
and ground wires are connected to the glass. Confirm
that the ground wire has continuity to ground.
(3) Check the fuses in the Power Distribution Center
(PDC) and in the junction block. The fuses must
be tight in their receptacles and all electrical connections
must be secure.

When the above steps have been completed and the
rear glass heating grid is still inoperative, one or
more of the following is faulty:
Rear window switch pod
Rear window grid lines (all grid lines would
have to be broken or one of the feed wires disconnected
for the entire system to be inoperative).
If setting the defogger switch to the On position
produces a severe voltmeter deflection, check for a
short circuit between the rear window switch pod
defogger relay output and the rear glass heating grid.

Posted on Aug 31, 2010

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1 Answer

My windows are not defrosting properly.


Do you have heat? Does the fan turn on? are you getting air from the defroster vents close to the windshield? If you have heat make sure the defrost control is working. I'd open the outside air vent and turn the blower on high speed. If there is no heat, the heater control valve is not working. Double check the radiator fluid tank, make sure you have enough fluid (antifreeze) Low fluid levels can reduce the hot water flow to the heater coil inside the car. If there
is no air flow through the defroster vents you may have a problem with the fan control, or the fan motor. Good luck.

Feb 20, 2015 | 2004 Chevrolet TrailBlazer

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No defrost on side mirrors or rear window


If you had defrosting previously, then first check your fuses.

If the fuses are good / not blown, then you may have had some other disruption of electricity / power to the mirrors / rear window.

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First check all fuses, second check for 12v power at the connector to th rear window, a test light or volt meter on dc voltage,if there is power use an ohm meter to check the window grid with the power connector disconnected.if open the connection is either open or bad. if there was no power at the connector check the power from switch all the way back to the window

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How do you turn on the heated mirrors


They are suppose to be automatic on the cars I know about. When the temperature drops to freezing, the heaters start working.

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For the defroster:

Turn the defroster on and check for 12v at the connector on the window. If you have 12v, check for breaks in the element (the thin lines running across the window). If you do not have 12v and the fuse is good, the culprit will most likely either be the switch or the wiring.

For the right park light:

Check the bulb socket. You should have 12v at one terminal (with the park lights on) and ground at the other. If the voltage and ground are ok, you either have a bad bulb or possibly a bad socket. By bad socket I mean they can sometimes distort and not allow the terminals to make good enough contact.

Hope this was helpful.

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2003 Trailblazer rear defrost connection loose from window..no defrosting or side mirror defrost


On this year vehicle the flapper should be vacuum controlled. You may want to look at the vacuum lines going to and from the vacuum canister in the engine compartment. If it will change from floor to dash but not defrost then you may have a failed vacuum line or diaphragm in the dash from the selector.

Feb 09, 2011 | 2003 Chevrolet TrailBlazer

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How can i fix the outside temperature? it's all time zero


  1. Turn ON the ignition.
  2. Simultaneously press the MODE, FRONT DEFROST and REAR DEFROST switches.
Turn the ignition on. Then press Mode, Front Defrost, and Rear Defrost all at the same tiem. It resets the sensor.

Jan 17, 2011 | 2002 Chevrolet TrailBlazer

1 Answer

The rear defroster doesn't work on 2005 Chevy Trailblazer. How do you find out if it the fuse and where is the fuse located?


I believe your fusebox may be located either under the rear left seat or in the engine compartment. If your defroster is the electrical type embedded in the window glass, then you may find that the problem is with the connection between the glass and the vehicle body. Typically when you close the window there are a series of brass contacts leading to the embedded wires that seat on brass contacts from the body. These contacts can get dirty. Sometimes just rubbing them with a pencil eraser to clean them off is enough to get things going again.

Nov 25, 2010 | 2005 Chevrolet TrailBlazer

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Need wiring diagram for rear defroster.


The common problem with the rear defrost not working on a park ave is the antenna integration modules on the rear c-pillars. This is the way they make the rear defrost and antenna part of the same grid on the rear window. If your external mirrors are heating up, the rear window is getting juice too. They are fed from the same circuit. And yes, the relay does go in a particular way. Compare it to the position of the others nearby and insert with the same orientation.

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Rear window defroster


ON THE REAR WINDOW YOU HAVE STRIPS OF RED WIRES BUILT INTO THE REAR WINDOW FOR THE OPERATION OF YOUR REAR DEFROSTS SOUNDS LIKE THERES A BREAK IN THE CIRCUIT YOU CAN BUY A REPAIR KIT FOR IT AT AN AUTOMOTIVE STORE YOU MIGHT BE JUST AS QUICK TO REPLACE THE REAR WINDOW WITH ONE FROM A WRECKING YARD

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