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[Taxi_Driver]

For car manufactures, to get the ecu to report the real problem! 

Went over to Mum and Dads today....Mum told me their Ford Fusion wouldnt start and could i have a quick look at it....

Its an 08 plate auto....so i tried it.....turned on ignition....ign lights on.....console beeped and display reported a 'Gearbox fault.....contact dealer'.

Tried to start it....it turned over a couple of times and gave up.....while cranking all the dash lights went off....

I tried it a couple of times.....same result...

So i decided battery was flat.....battery on charge....taking 12amps from charger.....3 hours later its down to 6 amps.....after lots of cranking and nearly flattening the battery again it starts 

So i take it on a 30min 10mile run to hopefully charge the battery fully....should be sorted 

But why ....couldnt the ecu have simply reported 'battery volts low' 

BTW the battery isnt knackered.....its simply what happens when all this car does is a weekly trip to the local coop, 1/2mile away and back.....doesnt have the time to recharge the battery after starting 

[Vamps]

I quite agree, surly when the battery you wold expect the ecu to know, after all in the Jeep a low battery was putting the auto box into limp mode, I never even though of battery as it started fine.....

In this case it did need a new battery, fitted and problem sorted.......

[martin42]

Didnt webby the bear,have this problem last year with his parents fusion,it wouldnt start because something needed topping up

[Nick W]

Doesn't an ECU work off the battery power? If that's so, surely there is a very good chance it won't work properly if the battery power is low?
Or should I have another go at explaining to my mother how mobile phones work?

[Taxi_Driver]

Theres another 'gotcha' with this one too...

I disconnected the battery to charge it.....so when i reconnected it the radio wanted the code for it....i looked for the passcode in the documentation.....i found the 'credit card' type card that stated code for radio/cd player......except it was blank....no numbers printed on it all....

I told my mum to ring the supplying ford dealer and give them stick for it.....ie ask for the code but dont agree to pay them money for it....it should be on the card.....but isnt 

[Taxi_Driver]

Doesn't an ECU work off the battery power? If that's so, surely there is a very good chance it won't work properly if the battery power is low?
Or should I have another go at explaining to my mother how mobile phones work?

Quite correct 

But in my simple way of thinking....the main ecu should check its own voltage level first and report that if not sufficient before reporting problems from other ecu's .....

[Vamps]

Doesn't an ECU work off the battery power? If that's so, surely there is a very good chance it won't work properly if the battery power is low?
Or should I have another go at explaining to my mother how mobile phones work?

Quite correct 

But in my simple way of thinking....the main ecu should check its own voltage level first and report that if not sufficient before reporting problems from other ecu's .....

And in my case, the battery gave no indication of a fault or of being low on charge, happily turning over starting a 5 cylinder diesel engine............. Now when I was a lad you knew your battery was flat, the car wouldn't turn over............

I, now, appreciate modern electronics need full voltage, so why can they provide an indication of a potential fault before going into limp mode........

[Marks DTM Calib]

Very understandable code in my opinion. 

Its an electronic setup and can only report fault symptoms.

In this case, the Engine ECU has reported that the gearbox is faulty, it might well be the gearbox ecu has a fault code for low volts.

The Engine ECU may be happy with how many volts it see's though as its connected direct to the battery or sees less volt drop when cranking.....or maybe made by a different company to slightly different voltage tolerance specs.

And hence why you have to apply knowledge and check live data, make some readings to confirm diagnosis.