FIXING AN ELECTRIC WINDOW ECU

t’s fairly common for the rear electric windows on a Discovery 1 to stop working. And while there are plenty of potential causes, including a blown fuse or faulty switches and connectors, usually the problem is down to a defective connection on the circuit board of the electric windows’ ECU.

The ECU is an awkward part to reach and extract for repair, so before removing it, it’s important to make all the usual basic checks of the circuits, even though we’re likely to end up at the ECU eventually. The first check to make is the main fuse. It’s at the top of the fuse board under the dash, and it’s the second one from the right on satellite 1, as the fuse group is called.

I checked the fuses (one for the front and one for the rear windows) on my own Discovery 1 which I’d bought with the rear windows not working. The fuse was okay but then, I expected it to be because it was only the two rear windows that weren’t working, with or without the child switch pressed. The fronts were fine, and that’s often the way the ECU fails, with both rears not working via the console switches or the door switches.

I always find with electrical fault-finding jobs, that I’m happier going logically

Ithrough the check procedures, even though some sections might not be necessary – it’s a way of knowing I haven’t missed anything. So now it was a matter of confirming the circuitry and switches before wrestling the ECU out from under the dashboard.

The first job was to connect a rear window circuit to a front window switch to test the switches and circuits. I removed the cable connector from the right rear window switch and swapped it over with the connector from the front right window switch and tried the systems. The rear window switch now powered the front window, but the front window switch wouldn’t run the rear window. That suggested there was no problem with the supply to the rear window switch, and no problem with the switch itself. So it’s likely to be an ECU fault.

The soldered connections in the ECU can fracture, causing an intermittent or permanent break in the circuits. They are quite delicate, especially after enduring a few years of road vibrations, and can even be disturbed by unplugging and refitting the harness connectors, so it’s important to work carefully. Of course, you can buy a used ECU from a breaker for around £30 and swap them over, but make sure it’s been checked for integrity. A new ECU will cost around £130.