K 2500 Truck 4WD V8-305 5.0L VIN M SFI (1998)
Heated Glass Element: Diagnostic Trouble Code Tests and Associated Procedures
Circuit Operation - Heated Outside Mirrors
When the Ignition Switch is in RUN, power is available to the Heater/HVAC Control Module BRN (141) from HTR-A/C Fuse 12 through the wire.
Also, power is available at all times to the Heated Mirror Relay contacts from the HTD MIR Fuse 2 through the ORN (140) wire. When the Heated
Mirror Pushbutton is pressed, the Solid State Timer actuates the Heated Mirror Relay to apply voltage through the ORN (1040) wire to both Power
Outside Rearview Mirror heating elements. Since the heating elements are both grounded through the BLK (150) wires to Ground G202, both elements
are energized. While the relay is energized, the local light emitting diode (LED) indicator is illuminated. The Solid State Timer times for 10 minutes
nominally, then de-energizes the relay. Depressing the pushbutton again re-initiates the timed operation. The relay is also de-energized with the Ignition
Switch out of the RUN position.
Circuit Operation - Rear Defogger
With the Ignition Switch in RUN, voltage is supplied to the Rear Defogger Switch at the Heater/HVAC Control Module. When the Rear Defogger
Switch is pressed, the contact closes, which provides voltage to the LED Indicator and the Rear Defogger Grid. The Rear Windows will heat to remove
fog from the surface of the window.
The Solid State Time Delay will automatically turn-off the Defogger Grids and the LED at the end of approximately 10 minutes. The Defogger Grids
are also automatically turned off if the Rear Defogger Switch is pressed again or the Ignition Switch is turned to the OFF position.
For the Suburban/Utility with Cargo Doors, the Defogger Grids can be energized only with the Cargo Doors closed.
Troubleshooting Hints - Heated Outside Mirrors
1. CHECK condition of HTD MIR Fuse 2 and HTR A/C Fuse 12. If either fuse is open, LOCATE and REPAIR cause of overload and REPLACE
fuse.
2. CHECK that Ground G202 is clean and tight.
3. If Power Outside Rearview Mirror heating elements operate, but the Heater/HVAC Control Module does not light, REPLACE Heater or HVAC
Control Module.
4. If the Rear Defogger Switch LED Indicator does not extinguish after a nominal 10 minute time delay, REPLACE Heater/HVAC Control Module.
5. SEE Interior Lamps Dimming, for diagnosis of indicators at Heater/HVAC Control Module. See: Lighting and Horns
^
CHECK for a broken (or partially broken) wire inside the insulation which could cause system malfunction but prove GOOD in a
continuity/voltage check with a system disconnected. The circuits may be intermittent or resistive when loaded, and if possible, should be checked
by monitoring for a voltage drop with the system operational (under load).
^
CHECK for proper installation of aftermarket electronic equipment which may affect the integrity of other systems. Refer to "General
Troubleshooting Procedures,". See: Diagrams/Diagnostic Aids
Troubleshooting Hints - Rear Defogger
1. CHECK to see that RR DEFOG and HTR A/C Fuses are not open. If open, LOCATE and REPAIR source of overload, then REPLACE fuse(s).
2. CHECK that Grounds G200 and G400 are clean and tight.
3. CHECK that Rear Defogger Grid(s) is continuous and free from damage.
4. If vehicle is not equipped with a Liftgate, then CHECK that LH/RH Door Contact Switch contacts are clean and free from obstructions.
5. If the Rear Defogger Grid(s) do not automatically shut OFF after 10 minutes, then the Solid State Time Delay Relay for the Rear Defogger Switch
may have failed.
6. If the Rear Defogger Switch light indicator does not illuminate but the Defogger Grid(s) defogs, the LED may have failed.
^
CHECK for proper installation of aftermarket electronic equipment which may affect the integrity of other systems. Refer to "General
Troubleshooting Procedures,". See: Diagrams/Diagnostic Aids
