Heated rear window: why it stops working and what you can fix yourself

The heated rear window fails in two ways: nothing works at all, or it heats in stripes. The second case is a half-hour DIY repair, and that is rarely known.

Nothing works at all

Check in order of cost:

The fuse — the heater draws a lot and has its own protected circuit; covered in the fuses article.

The relay — swap it with an identical one in the box.

The switch — does the indicator light? If not, the switch itself may be at fault.

The contact tabs on the glass — they are bonded to the elements and work loose with time. The most common mechanical cause, and it looks like “the heater burned out”.

The wiring to the glass — in the tailgate loom, where it flexes constantly.

The timer — many cars switch the heater off automatically after 10 to 20 minutes. That is not a fault.

Heating in stripes

The cause: a broken element. No current flows, and the whole stripe from edge to edge stays cold.

How to find the break:

1. Switch the heater on.
2. Mist the glass with water from inside or wait for it to fog.
3. Working stripes will dry; the dead one stays wet.
4. Inspect the dead stripe closely — the break is usually visible as a fine pale gap.

Another method: a multimeter on voltage — run the probe along the element; the reading jumps at the break.

The DIY repair

A rare case where doing it yourself is both simple and reliable.

What you need: conductive repair paint for heated screens (sold as a kit).

The procedure:

1. Degrease the area around the break.
2. Mask with tape on both sides of the element, leaving only the line exposed — that gives a clean edge.
3. Apply the compound thinly, overlapping the break generously.
4. Let it cure per the instructions — usually several hours, with the heater off.
5. Remove the tape and test.

What never to do to the glass

Never scrape the inside — the elements are on the inner face and a scraper tears them. The main cause of broken elements.

Never stick anything to the elements — suckers, mounts, stickers. Removal takes the element with it.

Do not clean with abrasives or harsh pads.

Do not carry loads pressing against the glass — the rules are in the loading article.

About the glass antenna

On many cars the same glass carries a radio antenna. Damaging the heater elements can affect it too.

A symptom people misread: “the radio went wrong after the glass repair” is often exactly that antenna.

What diagnostics shows

Body module codes — the heater circuit, relay, and switch.

System voltage — the heater draws a lot, and with a weak battery the system may inhibit it; covered in the alternator article.

Switch state in live data — to separate the switch from the power circuit.

In short

• Heating in stripes means a broken element, and it is a DIY repair.
• Wet glass shows the break in a minute: working stripes dry first.
• A scraper on the inside is the main cause of broken elements.
• Stickers and suckers on the elements take them with them on removal.
• Loose contact tabs look like “the heater burned out” but are mechanical.

Download the app — body electronics codes and voltage are read with an ELM327 adapter over Bluetooth SPP on Android.