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Discussion Starter #1
Has anyone got a circuit diagram/layout of the inside of the Pektron SCU/BCU for late MG ZR. need to see where the Horn and Rear Fogs terminate....cheers.....

Martin
 

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Mmmm....Rover..
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The rear fogs are simply powered via the SCU, the switching is handled by the fog switch.

The horn is either switched by one of the internal relays near the main connector or by one of the surface mount power FET's.

The easiest way would be to trace the circuit path from the pins on the main connector, pin 4 for the rear fogs and pin 11 for the horn.
 

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rover_45
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I do have a diagram but it wont help you as you wont be able to get the relay off the board without damage. I have tried. Also nobody sells one small enough to solder back on. You have to remember the company who make the unit have done cars relays and controls from the 70's onwards so they custom make there own stuff to fit as is the case with the relays.
 

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Mmmm....Rover..
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From experience it's rarely the control item (relay etc) at fault in these instances, usually a driver (transistor) or logic control problem.

The SCU seems to suffer from poor logic and software/firmware problems.
 

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Mmmm....Rover..
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Working on these dual or multilayer boards isn't difficult as long as you have the right equipment. I have sucessfully repaired quite a few 5AS and MEMS ecu's but having hot air SMD soldering gear is a must.

Sourcing the relays won't cause too many headaches, semiconductors and IC's can be a non-starter though due to OEM custom stuff, but in the case of the SCU i doubt that many of the faults are relay based!
 

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Discussion Starter #7
thanks guys was going to have a go at fixing it as im a weapon engineer however after xpart wanted the better part of £700 for a new scu and programming went for the cheaper £80 option of a bypass. popped the car into an auto electrician today 2 hours later horn and rear fogs working again, wasnt going to pay xpart that amount of money for just the horn and the rear fogs....everything else is fine. There was water damage to it but i had the dash out and found where it was seeping in and its all sealed up now...living up near Glasgow we have had the better part of a years rain recently and no more wet passenger footwell.....thanks again for all your advice...
 

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rover_45
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Excellant, just remember though the BCU will totally fail at some point.

Also with electrics Paul is your man, He has got me out of a few sticky spots in the past.

Top bloke in my oppinion and a credit to the forum like so many others.
 

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Excellant, just remember though the BCU will totally fail at some point.

Also with electrics Paul is your man, He has got me out of a few sticky spots in the past.

Top bloke in my oppinion and a credit to the forum like so many others.
So what you're saying is all us MKII 25/ZR drivers are going to break down soon ??
 

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So what you're saying is all us MKII 25/ZR drivers are going to break down soon ??
In a word yes the unit will fail. Its not just the 25/ZR its the SW and the 45/ZS and the TF too they all use this shoddy unit.

Some seem to be lasting more then others mind, I think it depends on how much water it takes on. My SW was still on its orginal but it was parked on a slope so water always ran off it. Also the early ones seem to be better quality as I have replaced far few of these then the later 54 reg cars onwards.

However my facelift 25 and 45 wear parked on the flat and they both had new BCU's under warranty the 45 had two in 3 months. After that I sold it as I couldnt trust the cars any more so the 25 went aswell.
 

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Mmmm....Rover..
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This is the downside of integrating all the electrical functions into one unit.

It makes economic sense for the manufacturer, but a disaster for the owner if the unit fails... more so if the replacement units cannot be trusted either.

A pity to see such a poor item coming from a respected manufacturer like Pektron, although I suspect the original was designed and built to a specific price which always reflects on quality and reliability.

I'm glad I have the old MFU and 5AS!!!
 

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AT what point did the SCU/BCU replace the MFU/5AS? Year / serial numbers, anyone know? I do know that it was after 617500 at least, as mine is the 5AS. Curious
 

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Discussion Starter #13
well the wife will probably only be keeping car for a couple more years so we will hopefully not have a total BCU failure in that time....

fingers crossed anyway
 

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In a word yes the unit will fail. Its not just the 25/ZR its the SW and the 45/ZS and the TF too they all use this shoddy unit.

Some seem to be lasting more then others mind, I think it depends on how much water it takes on. My SW was still on its orginal but it was parked on a slope so water always ran off it. Also the early ones seem to be better quality as I have replaced far few of these then the later 54 reg cars onwards.

However my facelift 25 and 45 wear parked on the flat and they both had new BCU's under warranty the 45 had two in 3 months. After that I sold it as I couldnt trust the cars any more so the 25 went aswell.

Are you now saying all cars leak water ? :)
If I am correct, mine on my left hand drive ZR is located behind the centre console, there is a box with hundreds of wires going to it, no water is leaking into my car so it shouldn't break down.
 

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Discussion Starter #15
i had water coming into my car via the joint on the bulkhead right above the SCU behind the centre console offset slightly to the passenger side(RHD). also had water coming in on the passenger side corner next to the heater matrix.....so mine was a water ingress problem..
 

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So what you're saying is all us MKII 25/ZR drivers are going to break down soon ??
I've locked horns with Sejin26 over this more than once before now...I think its a load of rubbish. Heck, what would I know, I only have a 3.5 yo ZR (that I can trust more than my brand new Cit.).
 

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Some seem to be lasting more then others mind, I think it depends on how much water it takes on.
So, hand on a minute....its becuase the unit gets drenched, not that its unreliable....its hardly the control units fault that it gets wet...

If I dropped my mobile down the loo, I'd expect it to stop working too - and I wouldn't blame its manufacturer (and condem all its products) for the fact it no longer works!
 

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Ok lets clear some of this up.

Early cars from 2003 53 reg to 04 04 reg are noramally a little more reliable and the BCU is abit more solid. Thats because the car uses two setups the older Honda one and the later Rover BCU setup. Infact some of these cars only use the BCU for the alarm and immobliser functions. The reason these cars fail is down to the BCU packing up on a software front. Mainly down to re-programming or electrical spikes.

The later cars from 54 reg onwards or face lift ones as some where on 04 too, So to make it easier all cars with the face lift dash and touch switchs are the ones that get effected by water ingress mostly. This is down to the re-made dash top which is not a perfect fit and with cheaper scuttle plate plastics whcih have cheaper seals.

These BCU's have to work a heck of alot more and either die due to a software problem like the early cars or they have a failure on the board which burns out and then causes the unit to play up or just die.

There is nothing anybody can do to stop it happening as its one of those things where one secound they can work happy as larry and the next there just dead.

If your asking me will they all fail. The answer is YES, they will all fail at some point and there is no set reason as to why and what triggers it off. It just happens.
 

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Ok lets clear some of this up.


The later cars from 54 reg onwards or face lift ones as some where on 04 too, So to make it easier all cars with the face lift dash and touch switchs are the ones that get effected by water ingress mostly. This is down to the re-made dash top which is not a perfect fit and with cheaper scuttle plate plastics whcih have cheaper seals.



If your asking me will they all fail. The answer is YES, they will all fail at some point and there is no set reason as to why and what triggers it off. It just happens.

I'm sorry but I don't understand what you are trying to say here, The dash is used to seal the car from the outside elements ??? Used to stop water getting in ??? I don't think so, yes there seems to be rather a lot of bulkhead leaks coming up, I had it on mine, the sealer was about 1 cm to low.


How can you possibly say that they will all fail ?
 

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I'm sorry but I don't understand what you are trying to say here, The dash is used to seal the car from the outside elements ??? Used to stop water getting in ??? I don't think so, yes there seems to be rather a lot of bulkhead leaks coming up, I had it on mine, the sealer was about 1 cm to low. How can you possibly say that they will all fail ?
Yeah, quite...its just that Sejin26 seems to be drifting between water ingress (not sure what the dash fit has to do with that - windcreen, maybe, but dash? No.), electrical failures (which are probably caused by the water ingress - electronics don't just short themselves out for no reason, same as with HGF) and firmware (software based in hardware) faults - software doesn't suddenly "break", if it doesn't work from the off then it won't "compile/run", and it doesn't suddenly decide to break itself either (testing would've eeked out the runtime faults, and there can't exactly be that many code paths to check)! Added to which in true MS style, a reboot would do the trick....

I don't believe the "they'll all fail" argument for one second!
 
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