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MG MGF Technical - blown fuse

My newly aquired F refused to start and on checking the fuse box under the bonnet found the green 30A engine management fuse (second from the top) had blown. A replacement fuse blew immediately. I am out bush here, anyone experienced this or have any suggestions of things to look at until I can get to help in the City?

No idea what your fault could be, but if you join( its free and takes seconds) you should find something in the archives.
Or check out Robs or Dieters sites, they are very helpfull!. :o).


IT sounds like that is Fuse 2 which supplies loads of things, so it is hard to say.

The Brown feed from the Fuse 2 goes through the Inertia Switch (LH side engine bay) and changes colour to Brown/Slate. Brown/Slate feeds the Alarm ECU (behind lower middle dash) and also the MEMS Relay unit (between the MEMS and the boot firewall) feeding in turn the fuel pump.

The Brown feed from the fuse also connects directly to the MEMS Relay providing the power for the Main Relay within the MEMS Relay pack. This in turn feeds various circuits within the engine compartment via Brown/Pink wiring. These circuits include the Injectors, the Ignition Coils, the Control Valves on a VVC, the Coil/s, the Purge Valve, the Stepper Motor and the supply for the MEMS itself.

So, like I say, hard to tell. YOu could try disconnecting some of the above and trying new fuses in a process of elimination to see if they blow.

GOod luck

Bruce Caldwell

yep hard to tell.
Recently we had someone in our German forum with the same F2 blowing failure.
In his case thae cause was a broken (or short ciruit?) Oxygen Sensor.
Try disconnectiong the Lambda Sensor. The interconnection is located just below the water rail drain bolt.
You need to open the engine bay and take off the air S-shape hose to the throttle body to get there.
Push in the wire clamp to release the female connector from the male side.

Just an option.
Dieter K.

Thanks Mark I've joined and searched the archives to no avail. Dieter, I got into the engine bay but despite your advice could not identify the sensor. I'll have another go when the workshop manual arrives and will bear your contribution in mind Bruce. The locals are baffled likewise the big city MG people. I will let you know the outcome when and if the happy day arrives and it is fixed---Roy

>could not identify the sensor.

Err, not the sensor directly, but the sensor _cable_ to it's first connector.
Male/Female .. *wire in, wire out* are calmped below the coolant rail.
Dieter K.

Welcome to the converted. I trust you will join the M.G. car club in your area most will have an F register so someone can help you or if not, guide you in the right direction.
Andrew Regens

Dieter - sounds the same problem that Tim Woolcott suffered from: the cable to the Lambda sensor had touched the exhaust manifold, melted the insulation, and shorted out - blowing fuse #2

Definitely worth checking out Roy :o)
Rob Bell

On my diagram it is Fuse No1 which supplies the Oxygen Sensors heated element via the Oxygen Sensor Relay's contacts, not Fuse No2. So bear in mind other reasons than a shorted Oxygen Sensor lead.

Perhaps I am wrong and Tim's Fuse No 2 was blown by the Oxygen Sensor signal lead being shorted to chassis.

Bruce Caldwell


I had a similar problem last year with my F.
sometimes it would run for days without blowing the fuse and others it would blow straight away....

It went to a Dealer, who couldn't find anything... and left me with the car to test.... it blew again...
I left the car over night and decided to look at it the next morning...
When I came to the car I pressed the beeper to unlock it and noticed that this worked form a much further distance than normal....
I replaced the fuse but when I pressed the bleeper this time it would not switch off the immobiliser.... until i got into the car....

I turned on the ignition and blew the fuse... and now the bleeper worked again....

I repeated the test several times..just to see if what i was seeing was correct...

the car went back to the Dealer on the back of a truck... and the next day the rang me to say that there was a bared wire on the immobiliser that was causing the short... it was fixed and has been OK since.....

just a thought if your still having problems..
Allan Inness

That's a very interesting report Allan - I wonder if this has anything to do with the MGF recall A169? (

I think that there may be more on this on Dieter's website as well if you have a look - the dash wires rub against the centre console 'subframe'. The immobiliser ECU is mounted under the heater box, so it is possible that the wires to this are vulnerable in the same way as were the pre-tensioner harness...
Rob Bell

Thank you Allan and Rob, most interesting in view of recent developments. The good news is that I disconnected the oxygen sensor after inspecting the wiring for shorting, and drove the car for 30 mins with no problems. The not so good news is that to confirm the problem, I reconnected the sensor and again drove for 30 mins with no problems. Oddly enough, with Bruce's comments in mind and before reading Allans commnents, I had taken a look at the alarm ECU and jiggled a few wires without actually doing anything. I think I will take a closer look as a nagging doubt spoils driving pleasure. Thanks to all thread contributors, will let you know.-----Roy
R Yeeles

This thread was discussed between 27/11/2004 and 02/12/2004

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