Does a faulty alternator affect the auto transmission?

[AndyH]

Hi folks, I've just acquired a '96 Bongo with a view to towing my sailing dinghy around the race meetings. I'm slowly becoming familiar with the beast having so far changed brake linings, exhaust and topped up the aircon (all it needed having never worked for the previous owner). Its a 4wd 2.5 diesel with the winter pack, 2 batteries and non functioning exhaust shutter doodad.

The most challenging problem is the constantly flashing hold light and absence of any kickdown from top gear. It goes into overdrive at about 38mph (its been converted to 17 inch wheels) and the only way to wake it up for the hills is to manually select lower gear. The hold button does nothing.

Yesterday I retrieved the gearbox fault codes using the excellent advice elsewhere on here and got codes 11, 12 and 16. 12 is the throttle position sensor but the other codes are not listed. Does anyone have any information on 11 and 16?

Having removed the link from the diagnostic socket I started the engine but then turned it off in reverse instead of park (not used to automatics yet, its been a while!). The vehicle was then all but lifeless and I found that the 100a main fuse had gone. The only way to avoid the fuse blowing again was to disconnect the alternator!

Did the diagnostic dodge finish off my alternator I wonder?

I drove it around to my garage with the alternator disconnected and noticed that the wipers and heater fan were working intermittently even whilst switched off.

Now the main fuse was intact but scorched looking when I bought the vehicle so perhaps the alternator had been dieing slowly for some time.

I'm now wondering, in view of the strange effects a disconnected alternator provided, whether a new alternator will cure my flashing hold light and lack of high gear kickdown.

A new alternator should arrive tomorrow.

All experience and wisdom gratefully appreciated!

Andy

[g8dhe]

There are lots of oddities there, I think one thing at a time to begin with!
You could get all sorts of strange things happening if the voltage from the alternator and battery was swinging around wildy.
No obvious reason why the wipers etc should work intermittently, with or without the alternator, it makes me wonder if you have deeper problems possibly even a damaged wiring loom if the 100Amp fuse has been overheating, but as I say at the beginning, tackle the most obvious faults to begin with but make sure that the garage do actually locate the problem and don't just swap things about until it seems to work and then find out later that they had merely disturbed things without finding the problem and solving it.

[AndyH]

Thanks George, however there is no garage other than mine.

Writing it all out has helped me in itself and now I think I'll check some earths whilst I wait for the alternator to come. There maybe some backfeeding going on somehow.

[Bob]

Geoff.

[Northern Bongolow]

short answer is yes it can.

[AndyH]

Well folks I swapped the alternator but the new fuse still glows red hot. However if I disconnect the double plug for the battery/sediment light the problem stops! The dreaded hold light is still flashing though.

Wiring diagrams next I guess.

[g8dhe]

Your disconnecting the field winding, this generates the magnetic field for the alternator to generate against. When you say that stops the problem do you mean the light goes out or that the fuse stops glowing ?

[AndyH]

The fuse stops glowing and the battery and sediment lights don't work at all - they simply don't light. Don't alternators self excite? Aren't there are permanent magnets on the rotor?

I guess I'll check the battery voltage with the engine running to make sure that the alternator is providing its 13.7 volts.

[g8dhe]

Don't alternators self excite? Aren't there are permanent magnets on the rotor?

No! The alternator generates 3-phase AC, which is immediately rectified and regulated to provide the DC supply for the vehicle and charge the battery,
See here for a helpful description https://www.howacarworks.com/basics/how ... stem-works

It sounds as if you replacement alternator might also be faulty, not unknown.

[AndyH]

Hi Folks,

Here's the latest!

I've tested my old alternator and found continuity between the output and the case and so I guess its goosed.
My new alternator doesn't have the same continuity.
The battery voltage with the engine off is 13V
The battery voltage with the engine running is 14V.
I think I can assume that the new alternator is working as an alternator should.

However that wretched 100A fuse is still glowing and blowing.

I pulled every fuse I could see apart from the ignition fuse to see if that helped - it didn't, that 100A just kept glowing.

I have purchased an 8 Amp charger today and it went straight onto full scale deflection as you would expect with a flat battery. So now I'm wondering whether the two batteries on my Winterpack Bongo (two starter batteries to cope with -40C North Japan Winters) got so flat with the old faulty alternator that the charge current is enough to blow the 100A fuse.

Please feel free to shoot my theory down in flames!

I'm going to leave it charging on trickle overnight and buy a handful of new fuses in the morning. Its currently drawing 2A on trickle'

Here's hoping!

[g8dhe]

Yes that is quite possible, infact very common, didn't the garage check the battery when they changed the alternator ?

[AndyH]

Thanks Geoff - I can sleep tonight encouraged!

There is no garage, I changed the alternator myself. Of course I didn't check the batteries....it started and everything worked....and I don't have one of those battery testers....

Perhaps tomorrow my problems will be over!

Andy

[AndyH]

That seems to have done it! No more glowing and blowing main fuse.

However I still have my flashing hold light and no kickdown for the hills.....

Thanks for your contributions Geoff. They helped me to think things through.

Andy

[g8dhe]

The Hold light flashng indicates that the computer has spotted a problem, there is a factsheet with details also this website http://www.philmcfadden.co.uk/MazdaDiagnosticBox.htm

[Northern Bongolow]

sounds like the problem is fixed, just clear the codes and it should stop flashing. battery off for a while and sit with your foot on the foot brake till the internal batt in the ecu goes flat then it should clear it.