Checking Maxi Fuses

[knotaclew]

Hi all,
I have a problem with an ABS light on the dashboard not coming on briefly with the ignition key.  I've taken the car to a dashboard specialist who has had it on the bench and fully tested everything and says the ABS light works fine when under test.  I've checked all the normal fuses but I suspect a possible power issue to the ABS ECU hence I'm wondering if a maxi fuse has gone AWOL.  Can't say I've ever noticed the ABS kick in on the pedal as I'm not heavy on the brakes.

So my question really is that although the Haynes manual says they must be checked by a Citroen dealer can I successfully check them myself.  I've watched videos on You tube showing maxi fuses on other Citroen's and how to dismantle the engine fuse box but it isn't clear if I'm time limited after disconnecting both the battery terminals and the flying positive lead to the fuse box.  My worry is that when I put it all back together something will have lost its memory and the engine won't start or something.

Please can somebody allay my fears or suggest an easier method of checking the ABS system.  I am about 4 months away from the MOT and I am concerned that a non operational warning light may send my faithful old girl down to the scrappy.

[Gadgetman]

I would rather suspect a bad wire somewhere than the maxi fuses.
I've only ever seen one such 'dealer toy only' fuses go on a car, and it took some monumental cockups by the guy mounting a breathalyzer/immobilizer thingie in a car.

[Sol]

Yeah they are monsters for a reason - they are high output so anything that blew them would show up elsewhere and there are only a few, each supplying a range of main distribution items so you would lose a lot of functionality if they went.

[knotaclew]

Yeah they are monsters for a reason - they are high output so anything that blew them would show up elsewhere and there are only a few, each supplying a range of main distribution items so you would lose a lot of functionality if they went.

Hi Zion,
Thanks for the reply.  Looking at the Haynes manual wiring diagrams I created a spreadsheet to determine which of the alphabetic fuses were involved with which system and indeed A thru D serve many systems but H serves only the ABS so that led me to think that, that may be the cause of my problems.

Referring to your reply regarding the BSI reset, I've tried that many times with no visible effect and I believe a garage tried the same but didn't get anything either.

I been to my local Citroen garage for a diagnostic test to be carried out but they say their equipment could not communicate with my car???  Still had to pay £50 for them to do it and then they wanted £? an hour to investigate the rest of he car which could have amounted to a load of dosh with no guarantee they'd fix the problem.  Same story from Halfords garage too.

So apart from the ABS problems, as I say in another thread I have problems with my windows (the intermittent problem could be a dry joint in the window relay??), map light not working, cigar lighter & 12v socket in the front (12v socket in the roof IS working), heated rear window not working.  Could all these be linked to the BSI needing a reset as you say?
Ignition barrel was changed about 4 years back, can't remember the reason and substituted with a breakers part, hence I have 2 keys on my keying (one for starting the car and another for opening the car locks and fuel cap).  Could this be my problem?

I have an ICarsoft OBD II that will communicate and look for codes but not with the ABS.  Oh an an earlier problem with the Airbag light was fixed with a new clock spring but when the airbag light wouldn't go out the 'monkeys' at the garage dived into the instrument panel and fixed it.  Needless to say when I picked the vehicle up the airbag light didn't come on at all and when I said it should come on briefly with the ignition I was told NO? I think your wrong there Sir!  Subsequently dashboard specialist found a broken wire and airbag light now behaves as it should.

[Sol]

Ah sounds like you had your work cut out with this motor eh. (No one needs a garage with those kind of tactics by the way!)

Ok then I think if you can see all ECU's (or more correctly controllers) except the ABS, then you could be right about fuse H, so I would thoroughly check every fuse for continuity, easier in the engine bay than the dash box, but after you establish all bad fuses are replaced, then the problems may all but disappear. Does your ABS lamp light up when you turn on the ignition? Non responding controllers can either mean fuse blown or maybe a damaged CANBUS comms cable (twisted pair usually red and white) if the controller itself is not faulty.

A BSI reset often fixes odd behaviour but the common faults depend on the model, mostly sidelights not working or not turning off, left/right indicator issues, central locking faults, headlights won't go off, wipers running by themselves etc.

ABS is a separate issue. Start with the basics and continuity check every fuse with a tester and go from there. Let me know what you find.

[knotaclew]

Ah sounds like you had your work cut out with this motor eh. (No one needs a garage with those kind of tactics by the way!)

Ok then I think if you can see all ECU's (or more correctly controllers) except the ABS, then you could be right about fuse H, so I would thoroughly check every fuse for continuity, easier in the engine bay than the dash box, but after you establish all bad fuses are replaced, then the problems may all but disappear. Does your ABS lamp light up when you turn on the ignition? Non responding controllers can either mean fuse blown or maybe a damaged CANBUS comms cable (twisted pair usually red and white) if the controller itself is not faulty.

A BSI reset often fixes odd behaviour but the common faults depend on the model, mostly sidelights not working or not turning off, left/right indicator issues, central locking faults, headlights won't go off, wipers running by themselves etc.

ABS is a separate issue. Start with the basics and continuity check every fuse with a tester and go from there. Let me know what you find.

Hi Zion,
Finally been able to get back to the ABS issues on the car.  I checked all the fuses that I could find and they were all OK.  I looked at some fuse box info on the forum which suggested the ABS ECU was powered via Maxi Fuse MF2.  I didn't really want to tear the engine fuse box apart to get to them so I managed to wangle the tray into such a position where I could touch the MF2 fuse.  There was a clear plastic top on the 50A fuse which came away quite easily and I could see the fuse wire as intact.  Unfortunately though I dropped the plastic top into the bottom of the fuse box whilst trying to replace it and thence it must stay until I have time to retrieve it.

So thinking out of the box, if I can't see the ABS light maybe I can force it to come on.  So I disconnected the Front RH sensor connector lead and switched the ignition on.  To my surprise the ABS light came on then after a few seconds went off with the airbag light and low fuel light.  Then started the engine and after a few seconds the ABS light came back on as it should to denote a fault with the system and turned engine & ignition off.  I reconnected the sensor lead, turned the ignition on and no ABS light at all.  I interrogated the ABS system with my iCarsoft tool saw the sensor fault and cleared it but still no ABS light.

I repeated the same on the Rear Offside wheel sensor and the same thing happened.  So now I know the ABS light is operational.  

I don't have enough car electrics knowledge nor brain power to work out why the ABS light only illuminates with a sensor fault whereas it should come on initially and go off every time I start the car like the airbag light does, any ideas?

Many thanks,

Knot a clew!

[Romahomepete]

I can make an informed comment about the maxi fuses

We had a complete electrical failure as we rolled onto a car park in the centre of Dinard one Sunday morning in our M59 based Romahome. Contacted the breakdown in the UK, they turned out their agent from St Malo. He arrived in less than an hour from a Renault garage drving a Land Rover. He had no experienec of Citroens.

He was a good mechanic though, he reasoned that we needed to find some large fuses. they were not immediately visible either under the dash or in the fuse box under the bonnet but tracing cables he worked out that they were under the main fuse box under the bonnet. He was spot on. The fuse board that you can see can be unclipped and raised up but not removed. The maxi fuses are under it. One was badly corroded and had blown. We fitted a replacement. I bought some spares and cleaned the fuse holders andholders when I got home. Checking those fuses is part of my maintenance regime now.

Both the handbook and the Haynes manual advise that replacing is a dealer job.

Peter

[knotaclew]

I can make an informed comment about the maxi fuses

We had a complete electrical failure as we rolled onto a car park in the centre of Dinard one Sunday morning in our M59 based Romahome.  Contacted the breakdown in the UK, they turned out their agent from St Malo.  He arrived in less than an hour from a Renault garage drving a Land Rover.  He had no experienec of Citroens.

He was a good mechanic though, he reasoned that we needed to find some large fuses. they were not immediately visible either under the dash or in the fuse box under the bonnet but tracing cables he worked out that they were under the main fuse box under the bonnet.  He was spot on.  The fuse board that you can see can be unclipped and raised up but not removed.  The maxi fuses are under it.  One was badly corroded and had blown.  We fitted a replacement.  I bought some spares and cleaned the fuse holders andholders when I got home.  Checking those fuses is part of my maintenance regime now.

Both the handbook and the Haynes manual advise that replacing is a dealer job.

Peter

Hi Peter,
Thank you for your comment about maxi fuses and I do agree this is where they are located.  As I said above I was able to check that maxi fuse MF2 was intact, only visibly, I'll admit.
But if MF2 wasn't working or corroded then that doesn't explain how by breaking apart a wheel sensor connector, the ABS light behaves as it should.  Then reconnecting the wheel sensor the ABS fails to operate?

Many thanks

Knot a clew (also a Peter)