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· Registered
21 Posts

I had the same problem with the int wiper function as described several times in this thread so I bought the replacement relay and replaced it. Now it works even worse because the wiper does not park, it stops where it was when I stop the wiper. It works well on first and second gear. Also I used to mimic the int wiper manually by hitting the controller (?) down once, it used to do the cycle once and park. Now it goes up and stops in the middle of the windscreen.
any advice?

ps. another replacement relay did actually worked for my central locking problems.

· Registered
4 Posts
Recently I have had some time to "play" with the Pektron SCU as fitted to the facelift models.

It suffers from problems that can be categorised roughly as follows..

Water ingress (25, ZR and Streetwise only).

Water enters where the wiring loom passes through the bulkhead, it trickles along the loom straight into the SCU. If the SCU had not been mounted with the connectors facing upwards you would simply have ended up with a damp patch on the footwell carpet!

Corrosion will be visible on the pins of the SCU connector. The first item to fail in the SCU when water enters is the radio receiver circuit board. It is mounted at right angles to the main board
and water will rest on it, symptoms include low fob operating range or no fob operation whatsoever.

If caught early the water ingress can simply be dried out and the SCU re-fitted.

If the SCU is damaged beyond repair then it is possible to copy the data from it and program this information into a new or used SCU, this process creates an identical clone of the original
unit and retains all features along with the original fobs.

With a bit of dexterity the SCU can be rotated so that the connectors face downwards and I would suggest that all owners of a ZR, 25 or Streetwise do this.

Fob and immobiliser faults....

A peculiarity of the SCU is that it will not allow diagnostics to communicate with it while it is in the armed state, therefore new fobs cannot be coded if it is armed and you have lost the originals or they don't work. I would assume that this was "designed" as a security feature, it's a pity that the dealer T4 diagnostics were not provided with a method of dealing with armed SCU's.

The MG-R solution when faced with this was to fit a new SCU and code new fobs, rather expensive.

Using a specialist diagnostic tool it is possible to program new fob to an existing SCU that is armed.

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).

Please take note of the following!

If buying replacement fobs please be aware that they MUST be supplied with a barcode label, the data on this label is required for programming.

Used or secondhand fobs that do not have this data are USELESS and cannot be programmed to the SCU, even if they are supplied with barcode information they still maybe unusable, see below.

When programmed the barcode data identifies the fob to the SCU, it also contains information regarding the rolling code that will be exchanged. As the fob buttons are pressed the code rolls forward but in a pseudo-random sequence that the SCU can follow. There is a "window" within which the barcode will still allow the fob to be programmed even after the fob has been used and the code has rolled forward. However if the fob has been in use for several years the code will have rolled forward so far that the barcode will no longer represent the valid starting point, it will program fine but not operate.

The fob data contained in the SCU memory changes as the code rolls forward, if this data is extracted and used to program fobs they will work fine as it represents the current "window" for
that fob.

Memory Loss...

I have seen quite a few units which have suffered loss or corruption of the configuration data stored in the SCU memory, depending on the severity of the problem you will be faced with one or more of the following problems;

Fobs are transmitting but they do not operate the central locking and/or immobiliser.

The engine starts and only runs for a few seconds.

None of the SCU based circuits operate correctly, for instance the drivers window operates in reverse etc.

Usually these problems arise after one of the following has happened...

The battery has gone flat.

The car was jump-started.

The SCU was disconnected/re-connected while the battery was still connected to the vehicle.


If the fob data is corrupt in the SCU memory there is usually no option other than to code new fobs, unless you are lucky enough to have a memory dump taken before the SCU became corrupt.

The engine running for a few seconds is a definite sign that the immobiliser code shared between the SCU and engine ECU is no longer correct. The two units must be security matched again to rectify this problem.

Inoperative options or circuits controlled by the SCU can be re-enabled if it is a software fault. In severe cases I rebuild the file using a known good base file and then add fob codes, immobiliser code and VIN details.

Circuit failures 1....

Circuits that cannot be switched off ie. horn or foglamps will not switch off, is caused by an electronic fault that keeps the relevant relay switched on constantly.

Circuit failures 2....
Horn doesn't operate.
Drivers window only travels in one direction or doesn't operate at all.
Rear foglamps do not operate.
Central locking only locks or unlocks... or does neither.
Intermittent wiper function does not operate.
Doors are deadlocked (superlocked).
Windscreen washers do not operate.

The last category is usually the fault of the Pektron branded relays, of which there are five.

The OEM (Original Equipment Manufacturer) relays fail because there coil winding goes open circuit which means that the relay will no longer operate when power is applied. I have dismantled many relays and
each time I have found that the very fine wire in the coil winding has fractured, closer inspection shows that it has corroded.

The wire used seems to be of poor quality with inconsistent enamel insulation coating, where the enamel is missing the wire corrodes.

Some OEM batches are worse than others, with various production weeks in 2004 being extremely prone to failure. I have seen replacement SCU's that were manufactured in 2008 and 2010 which still exhibit
relay failure so the problem still exists!

These relays are unusual by the fact that each single unit contains two separate relays. In instances where one physical relay controls two circuits, ie. one side controls the horn and the other the rear fog lights,
it is common where the horn side fails but the other side continues to work.

This picture shows the SCU circuit board and each relay has it's function shown...

10/2011: I now have stock of the exact replacement and much better quality relay, the Fujitsu relay that I previously
had stock of is no longer manufactured.

SCU Removal.

On all vehicles the SCU module was relocated or secured to withstand the Thatcham "5 minute" attack criteria, however it is relatively easy to access on some vehicle but a complete pain
on others.

The biggest challenge is when the SCU has to be removed from a 25 or ZR that has aircon fitted.

The SCU is fitted on the bulkhead behind the aircon evaporator housing. This is accessed by removing the glovebox,
the evaporator housing is towards the right with a metal retaining strap either side. The housing cannot be fully removed
as the evaporator contained within is connected by pipework to the AC system in the engine bay.

The original removal instructions were based on the fact that the early SCU bracket had a "hook" at its top which simply hung on a stud welded to the bulkhead.
All that was needed was for the lower housing nut to be removed, the housing pulled away from the bulkhead and the SCU lifted off the stud.

All change! The bracket was obviously modified at some point but the removal procedure was never updated.

The new design has a hole for the fixing rather than the previous hook and the bracket is now retained on the stud with a plastic cap. The aircon evaporator and housing has to be removed to allow access and SCU removal, this requires the system to be de-gassed and the pipework disconnected.

Here is the new bracket design...

Some people have managed to loosen the various clips and brackets securing the pipework in the engine bay, this allows more movement of the evaporator housing and slightly better
access to the SCU.

If the car does not have aircon fitted then it is easier to remove the plastic evaporator housing completely.

The procedure is as follows;

Remove the glovebox, two 8mm bolts secure the hinges to the metal framework.

Remove the metal strengthening strap that runs horizontally, one bolt either side.

The evaporator housing is to the right hand side.

Remove the two vertical metal straps. One bolt at the top of each strap and it is hooked in place at the bottom.

The housing is held in place with two 11mm nuts, one at the top and one at the bottom.

With these removed the housing can be pulled forward and removed.

Here is the SCU with the later type bracket in its position on the bulkhead, the hole on the left is where the aircon pipes enter.

On the 45/ZS the SCU is fitted behind the centre console, none of the above troubles here but there is a lot of dismantling required.

When the console has been removed you will need to unscrew the heater control assembly and the lower black plastic assembly from the metal framework, the SCU is located behind these.

The MGTF SCU location is also behind the centre console, roughly in line with the lower row of switches.
Remove the console side panel in the passenger footwell, don't pull it away too quickly as there is a wiring connection to the footwell light
that has to be disconnected.

The SCU retaining bracket only has to be removed on this side but the screw head is obscured by the bracket which is bent at 90 degrees.

Undo the screw, open the bracket and slide the SCU out.

The screws used are a variation on the TORX design, these are TORX-Plus Security which are a 5 lobe design with the pin in the centre.

The bit required is TORX-Plus 25.

Standard 6 lobe TORX security bits will not fit!

Here's a close-up of the screw head...

The correct bit can be difficult to source, if you cannot find one then get in touch as I have stock of the correct size.

In true MG-Rover style I have found the SCU brackets to be fitted with standard Pozidriv screws, 8mm hex bolts and the Torx-Plus screw!

Relay testing and removal.

Despite being a multilayered circuit board with through plated holes the relays are easily removed with a standard soldering iron and either a de-solder pump or de-solder braid.

The relay coil(s) going open circuit is the usual cause of failure. Each relay coil has two connection pins and a simple test is to measure
the coil resistance with a multimeter, a working relay coil has a reading of approx. 220 ohms.

I have yet to see damage or welding together of the relay contacts, despite their small size they seem to be able to cope with the current, especially the central locking and drivers window relay.

The picture below has the circuit board pads associated with the coil connections indicated with coloured dots, one connection (centre) of each
coil is "commoned" with the other coil.
If you put the black lead on the centre pin and alternately place the other meter lead on the pin to the left and then the right you should get
the 220 ohm reading each time.
If you don't then that side of the relay is faulty.

This particular SCU had no drive to the Drivers Window relay, the following picture identifies some of the drive electronics....

A is the driver transistor for the key fob transponder coil, the device is a T2406.

B is the transistor responsible for controlling the courtesy light, it is a BSP77.

The IC marked C is a TPIC6C595, it controls all of the relays with the exception of the relay handling the fogs and horn.

The IC marked D is also a TPIC6C595, it controls the Fogs and Horn relay.

All of these semiconductor devices are readily available components.

..... more to follow soon.


I can now offer full programming and repair services for the Pektron SCU/BCU.

Keyfob programming.

Enabling Central Locking, Electric Windows and Foglights.

EKA Code retrieval.

Extracting Key fob data

Unlocking an armed SCU/BCU.

Creating a "memory dump", basically a backup file of the data stored in the SCU, a must have if
you are faced with a corrupt memory at a later date.

Cloning units (ideal if you have purchased a secondhand unit or just want a second unit as a backup).

Forum supporters receive some of these services for free!


The self test mode is useful if you are having difficulties entering the EKA code, the drivers door lock switches (sill switches) are also the
cause of some central locking faults.

Taken from the original SCU Technical Training course documentation....

SCU Self-Test Mode

Self Test Mode can be entered manually as follows;

* With the driver's door shut, depress the door sill button.
* Turn the ignition on, off and then back on again.
* Lift the driver's door sill button.

This sequence of events must be completed within approximately 5 seconds. On successful entry the horn will sound briefly as confirmation and the vehicle will become immobilised.
Once the self-test mode has been entered, normal functionality of the SCU is suspended and certain alarm related inputs can be tested. A transition on any of the switch inputs will cause the security LED to flash briefly to acknowledge the input.
The following inputs can be tested by manual operation in this fashion.
* Sill up
* Sill down
* Passenger / Rear doors open
* Drivers door open
* Bonnet open
* Boot open
* Key barrel switches
* Inertia switch
Failure to access the self-test mode indicates a problem with the sill up, sill down or ignition switch inputs.
A spare key will be required to test the key barrel switch inputs, as one will already be required to turn the ignition on.

The information in this thread is given freely by me to help others, however I cannot abide by those who take this information and use it both commercially and claim it as their
own - to this end I have, from the very outset, introduced subtle minor technical inaccuracies. They do not take away from the usefulness of the information given but do show
up the idiots who claim to be but aren't technically knowledgeable to spot them!
If you want to use anything - just ask.
From reading this very detailed post, I think that chances are my SCU is damaged or out of sync with my ECU.
My key fob will not lock, unlock or de immobilise my MG ZR 2004.
I have the EKA but that does not work to deimmobilise it either.

I have tried to resync my fobs through many different steps found on the net. All to no avail.
It's really starting to tick me off now to be honest (no pun intended)

I read that you may have the knowledge and power to fix this problem, but knowing my luck you are probably based far away from me, as I live in north london... & with an immobilised car have no power to get to you.

But as a matter of despirocity (which is not even a word, which shows how frustrated I am), how much would you charge to fix my pektron SCU... And is there any way in heaven that you could become mobile????

Thank you,
From a stuck MG ZR owner

· Registered
'06 ZR +120 (HQM) '04 ZR 105 (IAB)
9,784 Posts

· Registered
4 Posts

· Registered
2 Posts
HI all, having read all 14 pages i am more confussed. my trusted 20003 TF was opened with the fob, but locked by the spare key. thjis may not be the issue. the fault is car unlocks fine, turns over, fires ofr 2 seconds and that you lot. i have found the EKA code. but the second digit is a zero, so how can you unlock Zero. reading the thread it appears the SCU is nottalking to the ECU. can these be re sync by me or does it need to go some where.

i must have read every blog on goole, but to no avail. when cranking the idle speed control clicks , no its notthe starter motor, you can feel ISC clicking as it rattles.

to synce SCU to ECU is it a simple process.
thanks every one,

· Registered
'06 ZR +120 (HQM) '04 ZR 105 (IAB)
9,784 Posts
As Sthar has posted in this thread, I assume he has a late 2003 TF with the Pektron SCU and round fob; in which case there is no resynch procedure. The engine firing up and then shutting down within a few seconds would suggest that the SCU has 'forgotten' the code it shares with the engine ECU to disarm the immobiliser. They need to have the code re matched which will require the services of an XPart Autoservice centre, current MG Motor dealership or someone else with access to a Rover T4 diagnostic computer.

Are you sure the number you have found is the EKA code? As it has a 0 in it, I doubt if it is, nor it may be that the 0 is actually supposed to be 10. You could try entering it as 10, and if that doesn't work, try enterin 1. There were problems with the codes for some earlier cars having the second a fourth digits entered on the database 1 lower than was actually the case.

If the car has a black squarish fob, it doesn't have the Pektron SCU but has the Lucas 5as security system, so the SCU specific problems won't be relevant. In this case, try the resynch procedure described by Talkingcars. It still sounds like a mismatch of the security code between the ECU/immobiliser and the security unit though; whichever system you have.

· Registered
188 Posts
ZS VVC horn fault

Since swapping the engine and wiring from a 2004, ZR 160 into a 2004, ZS We had to swap the ECU, BCU and fobs. Since then the horn has been constantly live so it's been unplugged from the horn itself. The immobiliser works as it should as does the engine.

Is this likely a BCU fault? The rear fog lights work as they should and I thought they were on the same relay.

Thanks for any info on this strange fault... :smile:

· Registered
'06 ZR +120 (HQM) '04 ZR 105 (IAB)
9,784 Posts
I think the horn sounding constantly is usually down to failure of a surface mounted i/c on the SCU circuit board - this i/c controls the horn relay. If a relay has failed, the item it controls doesn't work at all.

· Registered
1 Posts
Hey having a few issues hope you guys can help. Recently replaced scu and now my battery seems to be draining have changed the battery and the voltage regulator with no change so I'm assuming it's the scu causing this? Also neither front nor rear fog lights will come on and won't unlock by button but will lock. Will be sending scu to technozen soon but I'm not sure if battery issue/ front fogs are a separate issue. Cheers

· Registered
1 Posts
Technozen spot on

just to let folks know that I did some reading on this forum and following the info here I ordered 5 relays for my BCU as advised from Technozen on ebay ...changed them out and happy days .....fog lights now working ...central locking glitches fixed....and intermittent problem with drivers window also a big thank you folks

· Registered
1 Posts
Hi guys I'm new to the forum. I'm gonna be fitting front fog lights to my mk2 zs in the next few days. I have been reading up on it and it looks like I need to get the bcu reconfigured for front fog lights. I have 2 questions we have a gutman mega macs diagnostic tool that reads all control units and stuff.will that be able to configure bcu for fog lights to work? Next one is they we have a mobile key solutions gut(codes in keys and fobs and also cuts the keys) would he be able to configure bcu for fog lamps?? Thanks in advance

· Registered
'06 ZR +120 (HQM) '04 ZR 105 (IAB)
9,784 Posts
You need to visit someone with Rover Testbook T4 and the software applicable to the Rover 45/MG ZS. Any Xpart AutoService centre or current MG Motor dealer/service agent will have the necessary.

There are also several independent T4 service providers who are members of this forum and may be able to help you. Two who are well known and trusted are Phil T4 in Olney, Buckinghamshire, and marinabrian in Tyneside.

I don't think you will be able to activate SCU functions other than with T4.

· Mmmm....Rover..
10,420 Posts
Discussion Starter · #280 ·
Very few, actually none of the aftermarket diagnostic tools that I have seen can enable the SCU front fog setting.

T4 will do it.

I find T4 one of the most user unfriendly tools to use and rarely use mine, I find it much easier to enable the SCU functions at bit level in the memory data.
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