Above the rear left wheel arch, there is an earth point which is vulnerable to corrosion. Over time, water can get into the copper of the earth wires which hastens the cathodic reaction between the wiring and the earthing lug. Eventually, the wiring will disintegrate and break free from the lug. It is typical for the smaller diameter wires to break first but it is not obvious that they have failed until you start to investigate.
Symptoms that this earthing point is starting to fail include:
- The car will not lock on the key remote.
- Fuel pump failure (engine will suddently stop when driving) without displaying a single bar in the gear display.
- Multiple random engine electrical issues.
The first sign of a looming problem
One of the smallest wires which links to this earthing lug is for the central locking system. This runs all the way from the SAM unit. Why this was never earthed at the earth point neaest to the SAM unit is anyone's guess.
This earth only appears to be needed when locking the car on the key remote. When both doors are properly closed you will find that the locks try to lock but then immediately sping back to the open position. Note: it doesn't matter if the boot is open or closed when locking the car - there is no open/closed sensor in the boot lock. However, if you have drivelock activated or by pressing the lock button next to the hazard lights button, the car will lock correctly.
If you notice this behaviour, get this earth lug repaired as soon as possible before the more serious problems occur!
The potential major problem
The ECU and the fuel pump also use this earth lug. If any of these earths fail mid-drive, the engine may cut out suddently or you may find all sorts of random electrical issues occuring.
Systems which use this earth point
There are 8 earth wires which are connected to this earth lug. Wire sizes and cable colours have been given below if you need to graft in new wiring.
| No. | Function | Wire color | Wire size (mm2) | Connection point |
|---|---|---|---|---|
| 1 | ECU | Brown | 2.5 | ECU Connector 1 Pin 116 |
| 2 | ECU | Brown | 2.5 | ECU Connector 1 Pin 118 |
| 3 | ECU | Brown | 2.5 | ECU Connector 1 Pin 120 |
| 4 | ECU | Brown | 2.5 | ECU Connector 1 Pin 121 |
| 5 | Central Locking System | Brown/White | 0.5 | SAM Connector 8 Pin 2 |
| 6 | Fuel Filler Neck | Brown | 1.5 | Fuel filler neck bonding point |
| 7 | Boot Relase Solenoid | Brown | 0.5 | Boot lock connector Pin 1 |
| 8 | Fuel Pump | Brown | 1.5 |
Fuel pump connector Pin 3 |
Accessing the earthing point
Remove the rear left wheel arch liner and you will be able to see the earth point above the shock absorber. Use a 10mm socket to remove the retaining nut. You can see the in the example below that the wiring is alreay breaking away from the nut.
You can pull the wiring back towards the airbox where you can make necessary repairs:
If you find that there isn't enough slack to repair as you would like, disconnect the wiring harness from the fuel pump and the ECU. You can then pull the harness down into the wheel arch with a lot more freedom to complete the repair.
Once the repair is complete, we suggest covering the earth point and lug with water resistant grease to protect this point in future.