RRC MFU

Mercedeschris · Jan 1, 2023

Happy New Year to all.
Anybody know if you can still buy a RR Classic (1994 LSE 4.2) MFU?
I have a few issues with interior lights and rear bidet working intermittently and alarm going off.
I've tried 2 secondhand ones and they cure one issue but also add new ones. So I'm sure the MFU is faulty but so are the donor ones I'm trying.
So I'd rather just buy a known good one. Oh it's the black unit AMR 1280. Been on usual sites but don't see any new ones?

TIA

u

Disco1BFG · Jan 1, 2023

Any "new" MFU will be upwards of 24 years old now - so I wouldn't hold your breath..

If you have other variable issues then I'd suggest a good look at the alarm ECU - it contains a couple of relays which are known to fail - courtesy light issues being one of the clues to same..

The alarm can be fixed - this lot do so:-

https://www.technozen-electronics.co.uk/land-rover-10as-alarm-ecu-services/

The MFU, AFAIK can not! At least when I had trouble with mine it couldn't..

Disco1BFG · Jan 1, 2023

I'll add that I tried several MFU's too, but the issue was that I couldn't get any of them to go into self test mode - or to behave consistently..

Have you had a new alternator recently ? IMO, my problems started with same, and the VR in same being utter sh*te - both the set point and its abilities to regulate were completely wrong.. thus fried electronics

I replaced my MFU with relays and timers - lost some functions intentionally ( key in warning

- I mean, really? - who the **** could have put the keys in ??

)... Everything else works, and is easy to fix if it breaks - but it was a PITA job with a steep learning curve ...

Mercedeschris · Jan 2, 2023

Many thanks for the very useful feedback Disco1BFG. TBH my main and still outstanding issue was no rear wiper operation. Washer works but no wiper. Looking at the RAVE schematic the MFU supplies the rear wiper relay coil a ground to activate the relay. All my wiring is fine apart from this missing ground. Also my air suspension will operate with the doors open I know its not supposed to. When I tried my donor MFU this changed and EAS would only operate with doors closed. Also when the interior lights decided to work they only work on OSF drivers door. Again they work on all doors with donor unit fitted.
I'll check the alarm out when it warms up a little.....
Good point you made about a new MFU as you said its been sat in a box for 1/4 of a century now LOL never thought of that....

Disco1BFG · Jan 2, 2023

Mercedeschris said:
Many thanks for the very useful feedback Disco1BFG.

HTH - sadly I've got the friggin t-shirt with these damn things...

Mercedeschris said:
TBH my main and still outstanding issue was no rear wiper operation. Washer works but no wiper. Looking at the RAVE schematic the MFU supplies the rear wiper relay coil a ground to activate the relay.

All my wiring is fine apart from this missing ground.

I agree that the MFU controls the earths of the controlled circuits, mostly via relays - I had issues with the HRW circuit during the replacement of the MFU - it transpired that the wiring in the rear of the vehicle had become damaged - might be worth checking same - does the wiper work when powered independently ? I've seen the self parking brush drop to bits resulting in the wiper being kaput

Mercedeschris said:
Also my air suspension will operate with the doors open I know its not supposed to. When I tried my donor MFU this changed and EAS would only operate with doors closed.

Is the EAS inhibit circuit and associated switch, ( under the drivers seat ) ship shape and bristol fashion ? - I.E. free of verdegris ?

Do you have diagnostics for the EAS ? do they see an inhibit when the doors open ?

Mercedeschris said:
Also when the interior lights decided to work they only work on OSF drivers door. Again they work on all doors with donor unit fitted.

Will either MFU enter self test mode?

Mercedeschris said:
I'll check the alarm out when it warms up a little.....

Diagnostics should be able to talk to the alarm - and see each door open and close ...

Mercedeschris said:
Good point you made about a new MFU as you said its been sat in a box for 1/4 of a century now LOL never thought of that....

Ask me how I know

Mercedeschris · Jan 2, 2023

Yes the self diagnosis with HRW sw worked on original MFU, not tried the donor one yet.
Also I put a fused ground cable to the relay coil behind L/H foot well panel and wiper works. I've pin tested all connections on the C205 black connector all seen good

Disco1BFG · Jan 2, 2023

Mercedeschris said:
I've pin tested all connections on the C205 black connector all seen good

So, is issue that the MFU isn't grounding the wiper relay when it is "told" to do so ?

Mercedeschris · Jan 3, 2023

Yes. I see the rear wiper SW sends a feed to the MFU on pin 16 C205. I think the MFU is then spposed to ground the relay pin 85 from pin 23 C205 Blue/Orange wire. Have If I understood the schematic correctly.... So this is what made me comdemn the MFU....

u

Disco1BFG · Jan 3, 2023

Mercedeschris said:
Yes. I see the rear wiper SW sends a feed to the MFU on pin 16 C205. I think the MFU is then spposed to ground the relay pin 85 from pin 23 C205 Blue/Orange wire. Have If I understood the schematic correctly.... So this is what made me comdemn the MFU....

Agree on this^^ However, internally to the MFU, the logic determines that if the doors are open, then the wiper will not work ... I have fallen foul of this too - I forgot (!) ...

So, if your courtesy lights are mucking about, then the MFU might be seeing a door open condition, hence illuminating the courtesy lights, AND inhibiting the rear wiper..., which of course on a RRC would be a good idea if the upper tailgate were open

... which brings me back to your alarm being FUBAR ... or .... perhaps you forgot too

My Hawkeye can see the door open status.. do you have diagnostics ?

Disco1BFG · Jan 3, 2023

Your conundrum with the EAS / doors is also pointing to courtesy lights and thus alarm - I assume you have checked all the door switches ? .. As above - easy with diags...

Mercedeschris · Jan 4, 2023

Hi Disco1BFG. Your opening line made me think..."wiper will not work with door open" .......guess what I closed the door and it worked LOL.....I feel a right bird brain.... Once again thanks for your help we got there in the end. Can't seem to get it to work in diag mode though, but not bothered as everything is working fine ...all the best to you.

Disco1BFG · Jan 4, 2023

Mercedeschris said:
Hi Disco1BFG. Your opening line made me think..."wiper will not work with door open" .......guess what I closed the door and it worked LOL.....I feel a right bird brain.... Once again thanks for your help we got there in the end. Can't seem to get it to work in diag mode though, but not bothered as everything is working fine ...all the best to you.

Ha!! Welcome to the club..

Been, there, done that

...

If it won't go into self test mode, then you still have a problem!! ... which might be alarm related ... so worth checking out...

Mercedeschris · Jan 5, 2023

Agreed. Strange thing is with my old MFU the interior lights only work from drivers door if at all. EAS will operate with doors open. However it will go into diag mode and beeps from all doors etc?
The donor unit everything seems to work as it should be no diag mode. I'm going to take your advise and look at alarm unit wiring/connections. It looks like it fitted behind glove box.
Thanks again.

RRC MFU

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