Strange Electrical failure (now with video).

[rotorwings]

Posted earlier, but now I have more information on the problem:
- R300D
- Car will sometimes behave perfectly normally, start, etc.
- Car will sometimes refuse to do anything (as shown in video). No lights, dials, starting, etc.
- Sometimes when the car is running turning on an indicator, lights, or other electrical components will completely kill everything including the engine.
- The horn will always work.
- No voltage drop can be seen on the battery, so the battery itself does not seem to be the issue.
- I have charged the battery fully, cleaned all terminals and connectors.


Here is a video of the problem: https://www.dropbox.com/s/16jr2lq5z6ygbwg/CatElec....

Any help greatly appreciated!

[DCL]

Looks like a MFU relay failure. I suspect if you replace it all will be fine.

[rotorwings]

Sorry, what does MFU stand for?

I have swapped the location (moved them around) of all relays in the fusebox to see if that had an effect, but it didn't.

[DCL]

The MFU, or Multi Function Unit is a black box similar in size to the ECU. It contains a big relay that switch the main power on (except the horn for safety reasons). It is possible you car does not have one but it would have something to do the same function as the ignition switch is not rated for that sort of load.

[rotorwings]

Thanks. Do you know where I would find it if it exists?
I have an R300D (2012) with the push button micro-switch dash and a sterling immobiliser.

[DCL]

Google Rover MFU



Usually placed near the battery.

[mic]

Doesn't use an MFU. Your car has a control board with lots of potted relays. It should be mounted behind the dash on the vertical panel behind the heater.

[anonymous-user]

Yes, your switchgear is like the R400/500D.

I have a 400 with that dash and had a problem with the control board. Mine wasn’t the same fault as yours, the hazards would go on and off of their own accord.

Mine failed at about 6 months old. The replacement worked but it’s mounting plate was loose so CC sent me a third.

If yours is located like mine it’s screwed straight onto the bulkhead and subject to every bump and vibration. I don’t know whether or not that’s significant but I mounted mine on 4 anti vibration mounts on replacement.

Other than isolating it from vibration, it’s now a 5 minute job to change instead of having to move the heater. I also bought a spare board which should ensure the one in use lasts for decades.

[anonymous-user]

£172.54 + VAT

[rotorwings]

REALIST123 - I think you're right.

I've checked everything again with a new battery and got really excited because everything was working fine, but then it all started going haywire again.

Any idea what part(s) might be failing on the board? Are there ICs on it, or just relays? £175 is a lot if it turns out to just be a relay! I can't believe they don't make the relays replaceable.

[anonymous-user]

rotorwings said:

REALIST123 - I think you're right.

I've checked everything again with a new battery and got really excited because everything was working fine, but then it all started going haywire again.

Any idea what part(s) might be failing on the board? Are there ICs on it, or just relays? £175 is a lot if it turns out to just be a relay! I can't believe they don't make the relays replaceable.

Well the components are fitted to the board but then it’s heavily potted as the image shows. I’m not sure how easy it would be to change a component though it should be possible.

I think my issue was a latching relay that failed. I never knew which one, the board was replaced under warranty.