Technical Alternator issues

[koalar]

one of these is likely

5A near the diagnostic port. Under a cover to the right of the steering column on a rhd car

 

[Rollcage]

I was just looking at exactly those two fuses, and both appear fine. I will get my tester probe out tomorrow and see what each one gives. I'm suspecting a body Control module issue at this point, as the fuses all seem OK. Next step will be to locate the input and outputs of the bcm in the morning, if it's possible.

All a bit odd, I guess there could be a break in the wires somewhere.

Mamy thanks for your help with this Koalar, it's been invaluable.

 

[koalar]

First we need to workout if the fault is upstream or down stream of these fuses

normally fiat install fuses without the contact on the top, which is a pain as you have to remove them to check them

remove a fuse and turn the ignition on. The contacts on one side should measure battery voltage. With the Black meter lead on a Good chassis ground point. It is possible to use the ground on the obdii socket but they are quite easy to damage

adjust the meter to measure ohms. touch the two leads together if it registers something other than 0, say 2 ohms then across the fuse should be 2 ohms

It not unusual for the fuse to visibly look okay but for there to be a small micro break

 

[Rollcage]

Seems like it's a faulty earth. Tested loads of stuff today, and despite having replaced the negative lead I banged a jump cable on from neg to the block and it started charging straight away.

Slightly annoying it's so simple, but at least it's solved! Thanks for all your help Koalar!

 

[DaveMcT]

Zero charge without jump lead suggests the chassis to engine earth strap is disconnected.

 

[Rollcage]

Zero charge without jump lead suggests the chassis to engine earth strap is disconnected.

I will be having a look soon enough for sure. I know the battery to earth strap is there, but I didn't think to check the chassis to engine. When AI replaced the other one. I'll have a look Tuesday morning.

 

[koalar]

heres how I trace faulty High amp power or earth leads faults

I put the meter on the 2V range and measure either end while trying to push some current through the wire

in this case either end is the alternator case and the battery negative post. Clean a small patch on the alternator case and the battery negative terminal with a scotchbrite or wire wool.

0.1V is good
0.2V acceptable just
above 0.2V need looking at

May not work if there current to start the alternator but you can trace the fault like this

A to B
A to F
A to E

we may not be full at the source of the problem. If the gearbox earth wasn't very good the starter should turn slower or not at all. But it would surprise me if it doesn't find an alternative route

 

[DaveMcT]

My first car always started but the starter motor was slow. One day I rerouted the engine temperature gauge sensor tube as it was rattling (alcohol in metal tube type). The car wouldn't start at all. That's when I discovered there was no earth strap between engine and chassis.

 

[Jstott1070]

What a great forum.. had the 4x4 in the garage for 2 days swapping alternators in and out with no charging.. found this thread and tested myself and as soon as I connected the negative to the block - Bingo!! charging again!.. pulled batter and tray, removed both earthing cables (battery to chassis / chassis to gearbox) cleaned all contacts and put back, nice and easy. Back to normal charging - happy days.