Thread: D2a TD5 - low voltage when driving - sick battery or alternator?

im thinking alternator.
i dont have any knowledge on the td5 alternator if the rectifier is easy to replace sorry.

You will need to check your voltage at the main terminal on the alternator with engine running . A charging alt will give you 14.3 volts . Check your belt is not loose

Originally Posted by theelms66

You will need to check your voltage at the main terminal on the alternator with engine running . A charging alt will give you 14.3 volts . Check your belt is not loose

Belt is fine.

Will check the voltage on alternator terminal after work.

Have a close look at the stupid vertical battery terminals and see if they are actually tight or just look tight.
When I bought mine it stopped on the way home with the whole dash lit up from low volts, after the PO had spent hundreds on a mechanic looking for why the power steering stopped working. The bloody engine stopped that is why!

I had new terminals crimped on by an auto electrician and never had another problem.
Regards Philip A

Left work today and the voltage was back to normal while driving and the engine reving - 13.9 to 14.0volts. However when at a stop and the engine idling it would drop right down to the low 12’s.

Originally Posted by twr7cx

Left work today and the voltage was back to normal while driving and the engine reving - 13.9 to 14.0volts. However when at a stop and the engine idling it would drop right down to the low 12’s.

Intermittent voltage drop is usually the brushes in the alternator.
Thay are worn down and starting to fail.
Haven’t kitted a td5 alternator before but it shouldn’t be that different to most alternators.

Assuming that is the problem.

Paul

Originally Posted by twr7cx

Left work today and the voltage was back to normal while driving and the engine reving - 13.9 to 14.0volts. However when at a stop and the engine idling it would drop right down to the low 12’s.

I have the exact same problem with my D2a V8 and I am putting it down to the brushes in the alternator being worn out
I have ruled out the battery and the associated connections because I have tested the battery and have checked all the earth and power connections and all is Good.
I will be replacing the brushes as soon as they arrive and I will let you know if this fixes the problem

I had a similar issue with my 300 Tdi about a year and a bit ago.
Would charge for a short time after initial start, then stop dead.
key indicator that it stopped dead was the tacho would also stop(drop to zero).
Then randomly it may(or may not) have come good again for a few mins.

300 tdi is easy to run without the need for the alternator for a lot of klms tho.

I replaced the entire alternator, and all is well again.
Turned out mine was the regulator.
A previous attempt to fix it resulted in one tiny philips screw being chewed out, so the reg was a PITA to remove, and the quicker and easy option was to get a new alternator.

The problem with an alternator rebuild is, that if you just do the one part(eg. the brushes), another part(the reg/rectifier) is almost guaranteed to fail not long after reinstallation. and when you rebuild it again to sort that part, another part(eg. a bearing) will then fail after that reinstall.
TD5 alternator is not an easy job, when compared to a V8, or 300 Tdi.

As for a dropped cell in a battery, same D1 300 TDi, just a couple of months ago:
I got a Century battery Jan 17, and Dec 17 it started to show signs of a dropping cell. My D1 is my daily drive, but sometimes it may go for a full day and a bit without starting.
On those rest days, the next day it won't start on this battery(I have a dual battery setup) and I have to invoke the aux to get it to start.
Went back to get a replacement battery(10 min drive) and the knuckleheads at Supercheap 'tested it' and found it within spec.
That 10 min drive from my place gave the dying battery just enough surface charge to get it over the line(for them).

What should have alerted me to this dying battery was that it'd initially charge at 14.3-14.4 volts after starting up, but it would then quickly settle to about 13.2 - 13.5v once it had charged up and the alternator then went into top up mode.

Anyhow, I had enough of it causing me start issues, so pulled it, went back to Supercheap, luckily for me, the Century rep was there at that exact time! .. he tested it and found it had dropped a cell .. replacement installed and now I get the same initial 14.3-14.4(ish) initial start charge, and now it settles to about 13.9v after a long drive(as opposed to the old dying battery's 13.2-13.5v!

If the battery has a dead cell, if you leave it sit without charging at all for over a day, it will almost certainly not start the car(it won't have the capacity too).
If you try too start the car, with a volt meter on the battery, it's voltage may show 12 and a bit before you crank the engine, but during cranking it will almost certainly drop to below 10v.
A good battery will still hold above 10v during cranking.

It wouldn't surprise me if your alternator problem was intermittent during a drive.