Replacing a Range Rover Classic seat ECU

A non-working electronic seat on a Range Rover is more than just annoying – it’s an MOT failure and potentially dangerous, as Alisdair Cusick explains

THE pinnacle of the original Range Rover is often thought of as the Vogue SE models of the 3.9 EFI era. The earlier Vogue SE model of 1988 brought electronic adjustment to the front seats, but it was the models from 1991 onward that added a memory function to both the electronic driver’s seat and to the electronically-controlled door mirrors.

That was a long time ago, and today a number of issues can arise relating to the Vogue SE’S electronic seat system. Eventually, you will attempt to move the seat using the switch and nothing will happen. The bad news is that the driver’s seat must adjust forwards and backward in order to pass the MOT test.

You may never need to adjust the seat, but that doesn’t matter. It must work correctly, not just because the law says so, but also because the problem can cause further issues, such as the seat suddenly moving all the way forward, which is dangerous when driving. Note, the issue only affects the driver’s seat, and not the passenger seat which is wired directly to the car.

There are two main causes of a non-functioning driver’s seat. Firstly, the seat switch itself can fail. If you have a seat that moves in all directions bar one, then it is likely the seat switch just needs cleaning internally. Contact cleaner can simply be sprayed into the switch for the crudest remedy, but to cure the problem properly involves stripping the switch down. That’s not easy, thanks to the many small spring-loaded balls used inside it. But it is possible to either strip or clean the contacts, given enough patience – and you will definitely need plenty of patience. Alternatively, the seat switch is common to Mercedes-benz models of the era, enabling complete replacement with a new part.

The second issue is the big one. The driver’s seat has its own Electronic Control Unit (ECU), and its memory function requires a small battery. Over time, that battery inevitably leaks and the acid damages the tracks of the printed circuit board below it, and other components nearby. This issue will happen to all Vogue SE Classics, given enough time. The first sign will be a non-functioning seat, or mirrors, or both. Or, the mirrors might move as the seat is adjusted. If the problem is ignored, it is possible for ECU damage to cause the seat adjustment to randomly apply constant power to one motor in the system, which may happen when you are driving.

Opinion on fixing that issue is divided, and not helped by the fact that there is no wiring diagram available. Some owners report success by a mere clean of the area using contact cleaner. Others attempt a DIY repair, and there are repair kits available. But each failure is different and may need further components replacing, and will certainly require knowledge of the printed circuit board and its wiring. Tales of repairs that cure movement in every direction bar the vital fore and aft movement are legion. Wiring the power directly to the switch will likely cause the switch to fail in time, and this doesn’t get around the mirrors not working.

The alternative to a DIY approach is to fit a reconditioned ECU. You can purchase a reconditioned and tested unit, and send in your failed ECU on an exchange basis. This is what I did when I had the problem on my 1995 Range Rover Classic Vogue SE. I chose this route knowing it would provide a simplified fix from a specialist who understands the issue and, crucially, with a warranty on the reconditioned unit.

The symptom

In the case of my own Range Rover, the driver’s seat switch did nothing, in any direction. Nor did my electronic mirror switch, so I was confident the ECU had failed. Removing the ECU and opening it confirmed that the cause was leakage from the battery onto the circuit board.