P38A ALTERNATOR FAULT

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Grrrrrr

Grrrrrr

Technician, Bodgit & Scarper Ltd
Full Member
Posts
18,937
Location
Buckinghamshire, UK. ('95 DT)
Got in the car earlier and turned to position 2 and ALTERNATOR FAULT came up. Cycled the ignition and it didn't reappear.

Now, I am pretty sure it is just low battery volts but here's the question: does anyone know the triggers and logic that causes it to put that message up?
 
I would say it is just a low voltage or loose connection.....

Not sure what the trigger is, but I am sure it only measures the output voltage......if your engine wasn't running I can only assume it is a spurious message caused either by a minor undervoltage or a small electrical spike through the BeCM giving it a bit of a wobble.
 
Only connection to alternator when ignition is in position 2 with engine not running is D+ to voltage regulator. Bad connection to that maybe would bring up a fault.
 
No I am so used to it, all I do is turn the key back ant try again, and it doesn't come up again..... strange
 
Well, tried putting it on the booster charger last night. Today I had the same message and my charger says battery low, even after a 18 hour charge. Could be my low 13.6V setpoint has lowered the battery life. Maybe it has also strained the alternator? Or it could be corroded connections / bad wires or maybe the regulator itself has a diode that isn't quite right? Unfortunately I cannot do anything until my back is straight again.

However, I love the cranking with the CCA battery so I am thinking (when back has recovered and I can bend again):

Check voltage drop on wires from battery. Check all connections for corrosion.

@wammers, that kit you posted a while back to change in the alternator and increase the setpoint to 14.5V. Would changing that sort any diode issues too? Worth maybe swapping over to that and then maybe look at a new battery?

Anyone else electrically minded got any views? @martyuk , maybe?
 
Battery may not be charging properly - how old is it?

RE alt message. Signal wire lights up warning on dash at start up (12.5 v). On start up and if giving correct 14.5v is been given from alt will cancel out the signal to give a residual voltage, but not high enough to give warning. Fed through to the BECM
 
Grrrrrr said:
Well, tried putting it on the booster charger last night. Today I had the same message and my charger says battery low, even after a 18 hour charge. Could be my low 13.6V setpoint has lowered the battery life. Maybe it has also strained the alternator? Or it could be corroded connections / bad wires or maybe the regulator itself has a diode that isn't quite right? Unfortunately I cannot do anything until my back is straight again.

However, I love the cranking with the CCA battery so I am thinking (when back has recovered and I can bend again):

Check voltage drop on wires from battery. Check all connections for corrosion.

@wammers, that kit you posted a while back to change in the alternator and increase the setpoint to 14.5V. Would changing that sort any diode issues too? Worth maybe swapping over to that and then maybe look at a new battery?

Anyone else electrically minded got any views? @martyuk , maybe?
Click to expand...

What i posted was a voltage regulator with a 14.2 volt set point as far as i recall. If you have a calcium battery fitted 13.6 is nothing like good enough to keep it charged it may have sulphated the plates. 14.2 minimum 14.5 better. Maybe can be recovered with a high voltage extended charge at between 15 and 18 volts. But temp is critical it must be watched, if it starts to get hot it must be shut down and allowed to cool. Usually done with a special unit with thermostatic control. Fitting a voltage regulator won't do anything for diode leak backs. That needs a new diode pack. A refurbed alternator maybe a better bet but battery sounds dodgy.
 
Yes, my main suspect is the battery just not getting enough charge. I'll try and find the paperwork but I think it has probably been on there 4 years with 13.6V setpoint and occasional boost (every couple of months) from a decent charger.

Main reason I didn't fit the newer voltage regulator is I was cautious of the effect it might have downstream on fusebox etc. especially the fusebox given its age and it being an early car. TBH I'm still nervous about it. I guess you could argue it would only accelerate the inevitable. Options are a calcium free battery and put up with the lower cranking amps or upgrade the regulator and hope it doesn't have any unintended consequences on the no doubt drying joints in my fusebox.

Thanks everyone for all the comments. The way forward is a lot clearer now. I may even take the old battery and try shoving it on 16A and see of that shifts it but suspect higher volts rather than amps required. Cannot adjust that on my charger though.
 
Grrrrrr said:
Yes, my main suspect is the battery just not getting enough charge. I'll try and find the paperwork but I think it has probably been on there 4 years with 13.6V setpoint and occasional boost (every couple of months) from a decent charger.

Main reason I didn't fit the newer voltage regulator is I was cautious of the effect it might have downstream on fusebox etc. especially the fusebox given its age and it being an early car. TBH I'm still nervous about it. I guess you could argue it would only accelerate the inevitable. Options are a calcium free battery and put up with the lower cranking amps or upgrade the regulator and hope it doesn't have any unintended consequences on the no doubt drying joints in my fusebox.

Thanks everyone for all the comments. The way forward is a lot clearer now. I may even take the old battery and try shoving it on 16A and see of that shifts it but suspect higher volts rather than amps required. Cannot adjust that on my charger though.
Click to expand...
Try this mate, off the bay, worked for me 271072108072
 
Grrrrrr said:
Yes, my main suspect is the battery just not getting enough charge. I'll try and find the paperwork but I think it has probably been on there 4 years with 13.6V setpoint and occasional boost (every couple of months) from a decent charger.

Main reason I didn't fit the newer voltage regulator is I was cautious of the effect it might have downstream on fusebox etc. especially the fusebox given its age and it being an early car. TBH I'm still nervous about it. I guess you could argue it would only accelerate the inevitable. Options are a calcium free battery and put up with the lower cranking amps or upgrade the regulator and hope it doesn't have any unintended consequences on the no doubt drying joints in my fusebox.

Thanks everyone for all the comments. The way forward is a lot clearer now. I may even take the old battery and try shoving it on 16A and see of that shifts it but suspect higher volts rather than amps required. Cannot adjust that on my charger though.
Click to expand...

16 amps will be an higher voltage. Check the voltage across the battery when you have it connected to your charger. Alternator should be putting out 13.8 volts maybe the brushes on the regulator or worn pickup rings.
 
tomcat59alan said:
Try this mate, off the bay, worked for me 271072108072
Click to expand...

**** me. 14.7V!

Oh Jesus. I hate moving my car from factory settings. OK. I will give it a go.

To be fair it is running fine. Never would have noticed unless that message flashed on the dash. Mind you, bet it would have failed the first cold snap in the winter.

I will make a prediction now. This winter will be worse than the last one and either this one or the one after will be the worst in 5 years.
 
Grrrrrr said:
**** me. 14.7V!

Oh Jesus. I hate moving my car from factory settings. OK. I will give it a go.

To be fair it is running fine. Never would have noticed unless that message flashed on the dash. Mind you, bet it would have failed the first cold snap in the winter.

I will make a prediction now. This winter will be worse than the last one and either this one or the one after will be the worst in 5 years.
Click to expand...
I think battery technology has moved on since our car's were built.;):D
 
It's definitely worth having a look at the alternator and checking the voltage drop on both the +ve and ground cables from the battery.

I didn't know the Diesel alternators were set at a lower voltage - but if you have something like a MF31-1000 battery, which is great for the p38 power wise - they are a calcium battery and will need a higher charge voltage than what the set point sounds like it is on the Diesel Alternator.

I get 14.1V from memory at idle on my Thor 4.6 - and have had a MF31 battery in there the last 4 years with no problems.

The only not I can find in one of the BECM documents I have regarding the alternator charging signal is that it the BECM is expecting Ground/0V when not charging and Vbatt when it is charging. I haven't had an alternator apart to see where this feed comes from internally, but I would assume it's just a piggyback off the main +ve power stud.

I think the fuse box will be fine with the higher voltage too. Higher voltage actually means less current flowing (ohm's law). I wouldn't worry about other electronics either - most of the ECU's have their own internal voltage regulators to get the voltages they require to run, and I think from looking at a few of them, the inputs on most of the regulators are good for up to at least 30V - so a difference between 13.6 and 14.x shouldn't affect them too much.
 
martyuk said:
It's definitely worth having a look at the alternator and checking the voltage drop on both the +ve and ground cables from the battery.

I didn't know the Diesel alternators were set at a lower voltage - but if you have something like a MF31-1000 battery, which is great for the p38 power wise - they are a calcium battery and will need a higher charge voltage than what the set point sounds like it is on the Diesel Alternator.

I get 14.1V from memory at idle on my Thor 4.6 - and have had a MF31 battery in there the last 4 years with no problems.

The only not I can find in one of the BECM documents I have regarding the alternator charging signal is that it the BECM is expecting Ground/0V when not charging and Vbatt when it is charging. I haven't had an alternator apart to see where this feed comes from internally, but I would assume it's just a piggyback off the main +ve power stud.

I think the fuse box will be fine with the higher voltage too. Higher voltage actually means less current flowing (ohm's law). I wouldn't worry about other electronics either - most of the ECU's have their own internal voltage regulators to get the voltages they require to run, and I think from looking at a few of them, the inputs on most of the regulators are good for up to at least 30V - so a difference between 13.6 and 14.x shouldn't affect them too much.
Click to expand...

Thanks Marty. I printed the checks from RR.net last night and will work through those when I have free movement again.

still in China?
 
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