My rear passenger windows roll down by themselves when the car is parked in the sun. Could heat be affecting the electronics or switches? Is this a sign that my car’s wiring is failing, and could it drain the battery or even start a fire if left unchecked? Emmanuel
Hello Emmanuel, it is abnormal for passenger windows to roll themselves down while your car is parked in the sun. Whereas heat may be affecting the electronics or switch gear, there is a likely connection with a short circuit, and it is important to find out what is causing it.
There are three likely causes of the unauthorised car window roll-down: A faulty relay or shorting wire harness, a damaged or faulty driver master window switch, and a faulty window control module. Extreme heat, such as that from direct sunlight, can damage insulation or expand connectors of wire harnesses. This causes cross-flow of current, which can run the window motors. In the event that there is some moisture or corrosion build-up in the door harness connectors, usually caused by soapy water from jet car washing, it will cause short circuits that can give unauthorised signals to operate the window motors.
An inspection of the wiring harness by a qualified car electrician should be able to identify whether the short circuit is caused by the harness connectors or the relay box, to stop the unauthorised window roll-down.
Accumulation of moisture, dirt, or heat-driven expansion of plastic components of the master switch, especially in older cars, can cause unexpected roll-down of the windows, especially during the hottest part of the day.
This can be resolved by a mechanic removing the door card to inspect and clean the master switch contacts or replace them where necessary. A faulty window control module or convenience system remote can cause unintended window roll-down. Many vehicles today are designed with a convenience feature that allows you to remotely open all windows on a very hot day to allow the car to cool down before you enter it.
This feature can malfunction in the event that your remote is damaged and buttons stick, especially during a hot day, or the control module has short circuits due to moisture-driven corrosion or dirt build-up. A careful examination of the remote fob and internal control module can identify what is faulty for repair or replacement.
Intermittent, unintended roll-down of windows is a sign that there is something wrong with the window circuits, controllers, or switches, and it is an indication that there are circuits that continue to run power even when you have switched off the car. This situation is called parasitic draw of power, which will drain your car battery over time and weaken or damage it.
A faltering battery during a cold start or warm window switches is a sign of parasitic power draw. A technician can investigate this with the right tools and find the cause. Any short circuit can cause heat build-up and, in extreme cases, start a fire. Short circuits should be fixed as soon as they are identified to avoid accidental fire outbreaks.