20 October 2022
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ECU is located under the seat
: credit: © Alisdair Cusick
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
Need to know
Time: 1 hour (swap), 4 hours plus (repair).
Difficulty: For a straight swap: 1 out of 5 stars; For a repair: 5 stars
Models: Range Rover 1991-1995.
Tools needed: Allen keys, Torx bits and ratchet, Phillips screwdriver, side cutter pliers, cable ties, multi-meter, spanner set.
Parts needed: PRC9864 (FF010049 at Famous Four); £586.80 plus £240 exchange surcharge.
Work safely:
• Always disconnect the battery earth before working on a vehicle’s electrical systems.
• Use the right tool for the right jobs.
• Always be fire safe in the workshop.
• Understand wiring fully before powering up an electronic system – if in doubt, confirm correct operation using a multi-meter.
• Get an expert to do the job, if in doubt.
Thanks to: Famous Four for its help with this feature: famousfour.co.uk.
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.
Removing the ECU
Safety first: Having confirmed the non-function of the driver’s seat and mirror switches, the first step is a basic one – disconnect the battery.
Rule everything out: To rule out the simplest cause of any non-functioning item, check its fuses. Here, the electronic seat fuses are under the rear of the driver’s seat.
Meter practice: With a multi-meter, check for continuity across the fuse blades, putting a probe each side of the fuse. No continuity confirms a blown fuse – so no power.
Take a seat: The fuses here are okay, so we access the ECU under the driver’s seat. The seat is held by a socket head bolt on the front fixings for this 1995 car.
Not all are this easy: The rear fixings are Torx bolts. Some model years have less accessible fixing locations, meaning the seat motor may need powering to move the seat for access.
If the seat cannot be powered normally, disconnect the ECU, then use a jumper lead to power the relevant motor. Alternatively, manually drive the seat motor by disconnecting the seat motor drive cable and using a drill or similar to rotate the cable, thus moving the seat.
Tilt and rest: The seat can now be raised up and tilted backwards to improve access, carefully resting the rear seat brackets on the top of the fixing mount.
ECU: Now we see the ECU on the underside of the seat. Take a photo, or draw the cable positions and cable-tie fixing points, to refer to later.
Simply undo: Release those connectors that you can access easily. There will be some cable ties, so cut those carefully with side cutter pliers, seen here.
Remove: Twist the single fixing on the right-hand side, and slide the ECU out, complete with original identification tag (from Feb 1995). Release any remaining connectors.
Investigating the problem
Open up: On the bench, we need to open up the ECU. Note this unit’s tamper seal is still intact, usefully confirming it hasn’t been tinkered with before.
Board game: Lift off the lid, then carefully lift up the circuit board. Don’t pinch or crack anything. There are two grommets to be guided upward as the board is lifted.
Identifying the cause: The battery leak is clearly evident. This is one of the very last Classics, so expect worse on earlier model Range Rovers, especially if the symptoms were ignored.
The problem: It looks minor, but leaking battery acid has spread and corroded the circuit tracks. If left to fester, it can cause an electrical short or damage nearby components.
Installing the new ECU
Old and new: Failed unit (left) and reconditioned unit (right). Always confirm part numbers against model year. The recon unit is 1991 (earlier than mine), but the memory function is identical.
Work slow, work well: At the car, connect up the ECU to the seat loom. Ensure the connectors lock together, but plastic can become brittle with age, so be very careful.
Back in place: The ECU slides into a locating peg on the left-hand side. Lock it in place with the clip on the right. It might need a shuffle to locate.
Final connections: Route the wiring comfortably in place, then reconnect any remaining wiring. The large connector block fixes to the seat base with a rather awkward clip.
Out of harm’s way: The final wiring job is to re-secure the wiring neatly with cable ties so it cannot catch on anything when the seat is moved backward and forward.
Last jobs: Refit the seat, then double-check that the wiring won’t catch on anything nearby. Lastly, as we’ve finished working with wiring, we can reconnect the battery.
Moment of truth: Test the seat for movement. Fore and aft needs to work for the MoT test, but all functions should be restored. Also, confirm the mirrors work correctly.
Alternative cure
United States LRM reader, Chris Wagner, solved his driver’s seat issue an alternative way. After researching the possible solutions, he asked a local specialist to repair the ECU, removing the troublesome batteries in the process. Removing the batteries disables the memory function, but it prevents the issue reoccurring in the future, and the seat and mirror switches continue to work as normal.
Latest options
At the time of writing, Range Rover specialist Famous Four is investigating options for having the seat ECU printed circuit boards remade. Check out its website for part number FF010049, and for updates on the remanufacture option: famousfour.co.uk.
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