987 Water damaged rear body control module
When rear modules become water damaged, they can activate the roof as well as other functions whilst the vehicle is parked and locked. This can activate the roof whilst it is in the locked position. It frequently breaks one or both of the ball joints on the control rods, and sometimes bends the control rods. Other symptoms can include the rear spoiler and back lights activating when the car is locked.
Ensure you locate and fix the cause of any internal water leaks that cause the water ingress – this is often blocked roof drainage channels.
Occasionally the rear modules can be dried out and coaxed back into life, but usually they are damaged and require replacing.
Whilst used modules can be used and reprogrammed it can be difficult to obtain a good quality unit that is not also damaged. Prices vary but are typically be in the region of £150-£300. A genuine new item costs around £330 including taxes (as of Nov 2021). If the donor vehicle is not an identical specification to the recipient vehicle some form of reprogramming is usually required to ensure full functionality of the module.
The rear control module is located under the passenger seat. To remove it undo the Torx bolts from the seat runners and either remove the seat completely, or to tilt the seat back forwards and then manoeuvre the complete seat back so access to the module can be gained.
There is a multi-connector which attaches to the seat, if this is removed whilst the battery is connected the vehicle's airbag light will be illuminated. Disconnecting the battery first will prevent this from happening.
(NOTE - occasionally when disconnecting the battery a “vehicle handover” procedure may need to be carried out by diagnostic equipment due to loss of functionality of the heated seats and headlight washers.)
The rear module is located in a black plastic carrier in the seat well. Remove the carrier by undoing the retainers and turn it over where you will see the module. It is clipped into place in the carrier – remove the connectors first then manoeuvre the module free.
Replacement is the opposite of removal.
When installing a replacement module, ensure the ignition is off and the key removed. Replace the module into the housing, re-connect the connectors. If the seat connector has been removed, then reconnect it prior to reconnecting the battery to avoid the airbag light turning on.
Lock and unlock the vehicle – this allows the rear module to reset and communicate with the other modules in the car and boot up properly. Not doing this can introduce problematic communication errors.
Next test the functionality of the rear spoiler, rear lights and roof.
There have been rare occasions after replacing the rear module that it fails to ‘find’ the roof position. If you have suitable diagnostic equipment activate the roof function from the diagnostic computer and cycle it open and shut (with the latch unhooked and after replacing the ball joints/control rods as required). This is usually sufficient for the module to interpret the roof position and to operate correctly again.
Note – if one of the ball joints on the control arms has broken it is highly likely that the other ball joint will also break when using the roof. To minimise costs, it is recommended to replace any broken ball joints before trying to activate the roof.