MG-Rover Pektron SCU - BCU.

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The Pektron BCU (Body Control Unit) was fitted to MG-Rover vehicles from 2003 until 2005.
This unit controls all of the body electrical circuits including the immobiliser, the unit is also known as the SCU (Security Control Unit).
Vehicles that use this unit have an oval fob with the manufacturer logo in the centre.

I have spent a lot of time on this unit and I know it very well, faults and fixes, method of operation and by studying the circuit board I have been able to create a full circuit diagram - invaluable for fault finding.
There have been several issues with this unit and they can be roughly divided into three categories;

Internal Relay Failures:
The BCU contains five dual relays, they switch the following circuits;
The fault with each circuit is given in the brackets ( ).
Drivers Electric Window (Window only operates in one direction or not at all)
Central Locking (Vehicle locks but does not unlock, or vice versa)
Horn (Does not work).
Rear Fog Lamps (Will not switch on).
Windscreen Washers. (Do not operate).
Intermittent Front Wipers (Do not work).
Superlocking. (Doors cannot be opened, superlocking cannot be cancelled).
The original relays were manufactured by a third party company for Pektron and carry the number 0662P04A.
These relays are a common component to fail. The OEM relay that Pektron used had poor quality enamelled
wire in the coil windings, this corrodes over time and the relay fails. I have seen replacement units manufactured
relatively recently with the same relay failure.
I have replacement relays from a different manufacturer for sale on Ebay, please see my listings.
Water Ingress Damage:
This only affects the Rover 25 and MG ZR. 
In these vehicles the BCU is mounted with its connector facing upwards, water enters via the wiring loom
and easily trickles into the BCU.
Faults can be minor, which cleaning and repositioning of the BCU will solve OR worst case where a replacement 
BCU is required. 
I can repair all BCU faults and it is rare that I will suggest that a replacement is required.
Fob Failure:
As with all vehicles and manufacturers the alarm/central locking fob can lead a hard life.
Fobs fail, are lost or you might simply decide to have extra fobs added. There are some peculiarities with the Pektron unit.
The BCU must be in the disarmed state to allow suitable diagnostic equipment to communicate with it. If it is armed (dash LED  flashing) you cannot have fobs coded, this is usually the case if all fobs have been lost or do not work.
A special diagnostic tool can be used to program fobs to an armed/locked SCU.
New fobs must have a barcode label with them, this information is required for coding. Used or Secondhand fobs cannot be used.

A design problem means that fobs that were programmed and working can become corrupted, this was a known problem when MG-Rover existed. The corruption is caused when the fobs are on the same keyring as those from the following manufacturers;

Any BMW vehicle.

BMW Mini.

Rover 75/MG ZT (Immobiliser is a BMW based system).

These vehicles use a transponder based system to communicate with their fobs, the transmissions corrupt the 
Pektron fobs rendering them useless.
DO NOT keep MG-Rover Pektron fobs on the same keyring with any of the above.

In these instances the only solution is to program new fob(s).

Other Faults:
If the vehicle horn sounds continuously the fault is caused by an IC failure, not one of the relays.
This control IC is numbered TPIC6C595 and is a readily available component. However it is a
surface mount component and skill is required when replacing it.
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