Yesterday a red alert flashed up on the dash indicating an alternator fault (I forget the exact wording). Within a couple of seconds it was gone. This was after a decent motorway run of half hour or so if that's of any relevance. Following fault codes from IID:

P0A1A-87 (40) Generator control module - Bus signal/message failure - missing a message
( on 09-02-2024 15:57:38 at 140318 mi )
B1087-93 (2 LIN bus A - Component failure - no operation
( on 09-02-2024 15:57:38 at 140318 mi )

No issues on the journey home, but wondering if this points to imminent failure of alternator and/or battery? Alternator is around 3 years old, and new battery 2 years ago.

Any thoughts? Thanks in advance. 2011MY 4.4TDV8 Autobiography Baltic Blue
TVR Griffith
Alfa Romeo Mito QV

I had similar and it gradually started happening more often and eventually it came on permanently at which point, I replaces the alternator and all was ok, so I would suggest you might be on borrowed time. Got - 2017 SDV8 Autobiography in Loire Blue
Had- 2008 TDV8 Vogue SE in Java black
Had - 2007 S/C in Stornoway Grey

Thanks alarm_3, not what i wanted to hear! Surely alternator should last longer than 3 years? Fault came up again three times today and cleared almost immediately. Dodgy connection somewhere? 2011MY 4.4TDV8 Autobiography Baltic Blue
TVR Griffith
Alfa Romeo Mito QV

Update - still getting these pesky codes popping up. After careful monitoring established the following:

1) The fault code only appears after 40 - 45 minutes driving
2) The fault stays up for up to 4 minutes before clearing itself and then randomly reappearing.
3) Voltage prior to fault 14.5V, when fault is up drops instantly to 13.7V, back to 14.5V when fault clears.

As mentioned, alternator was replaced 3 years / 15,000 miles ago. My amateur diagnosis errs towards a dodgy connection - as it heats up, resistance increases to a point where the system assumes a fault. Or a slipping drive belt, expanding and losing tension as it heats up?
Charge voltage of 13.7V does not seem excessively low to me (normal on my TVR), but obviously something is awry.
Indie is keen to fit a new alternator (well, he would be wouldn't he?!).
Thoughts?


Edited to add, KwikFit Bosch battery tester results: voltage 12.75V rated 850, measured 654, IR 3.57mOhms, cranking power 77%, state of charge 87%, cranking voltage 10.62V, load on 14.59V, diode ripple 0.07V 2011MY 4.4TDV8 Autobiography Baltic Blue
TVR Griffith
Alfa Romeo Mito QV

it may be as simple as sticking brushes inside, easy to check/fix once youve got the alternator off, the latter being the bulk of the work. Yes it should last a lot more than 15,000 miles. It is also possible as you state to have a broken control wire etc.

The joys of RR ownership

Good luck. BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

Two 90 minute runs over the last couple of days and no fault codes to be seen. Gotta love these self fixing cars! 2011MY 4.4TDV8 Autobiography Baltic Blue
TVR Griffith
Alfa Romeo Mito QV

Like most things in life, if it sounds too good to be true it usually is. The alternator fairy may be having an Easter break  BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

As predicted, the fault has returned after the Easter break. Still not dropping below 13.7V when the fault appears, car still running, battery still charging. What could possibly go wrong ...? 2011MY 4.4TDV8 Autobiography Baltic Blue
TVR Griffith
Alfa Romeo Mito QV

A lot  Got - 2017 SDV8 Autobiography in Loire Blue
Had- 2008 TDV8 Vogue SE in Java black
Had - 2007 S/C in Stornoway Grey

If your car has any kind of intelligent battery management system used I would look there for the culprit. Voltage dropping to 13.7 every time could indicate that the battery management unit has an intermittent connection to the alternator regulator. When this happens the regulator defaults to 13.7volts which is more than enough to fully charge a 12v battery without damage. 2003 TD6 HSE. 161,000 miles

Heed the warning signs - get a new alternator  2012 TDV8 Vogue (L322)

steve k wrote:

If your car has any kind of intelligent battery management system used I would look there for the culprit. Voltage dropping to 13.7 every time could indicate that the battery management unit has an intermittent connection to the alternator regulator. When this happens the regulator defaults to 13.7volts which is more than enough to fully charge a 12v battery without damage.

It will be connected to the battery terminal/s. I'm not familiar with the type used on your model.

You might actually try disconnecting it to see if it flags the same error codes and results in 13.7v at the battery?

If it were me I would do some basic continuity tests between the relevant connections at the battery to the alternator, access to a wiring diagram will tell you what wires and colours etc. 2003 TD6 HSE. 161,000 miles

…..but in the end you’ll probably still replace the alternator. My first replacement, that I did myself, as I did with the latter one, in the middle of winter some years ago, “only” lasted 3 years and it was a “proper” one, so it’s all down to fate, not time

If you have any thoughts on doing it yourself, do it in summer, your hands and arms will thanks you. Got - 2017 SDV8 Autobiography in Loire Blue
Had- 2008 TDV8 Vogue SE in Java black
Had - 2007 S/C in Stornoway Grey