1997 4.6 HSE No charge light after fitting new alternator

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jdennington

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OK this one has me stumped, my old alternator bearings were getting noisy so I decided to change this before it let me down. Fitted new alternator only to break down on the way to work. RAC ran some checks and reported that diode pack was faulty as there was no charge light showing on the dash and just 11 Volts going to the battery. If the thin brown/white wire connected to the W+ terminal was put to earth, the charge light would illuminate. Another new alternator fitted tonight only for me to find that there is still no charge light showing on the dash. Changed the charge light bulb for know good one, still nothing. Reading on the battery with the engine running gives me 13.7 - 13.9 Volts so appears to be getting a charge. There are only two wires going to the alternator, one large red which will only fit to one terminal and one thin brown/white wire which is going to the W+ terminal. I get a closed circuit to positive if I test the red wire and a closed circuit to earth if I test the brown/white wire. I also get a good earth circuit to the alternator body. The negative terminal of the battery was disconnected for each removal/refit of the altrenators. I get an "ALTERNATOR ERROR" show after a while if I dont start the engine but no error if I do. The test on both wires would seem to suggest that there are no breaks in them. Where else should I check, and would the "ALTERNATOR FAULT" error stop the charge light from showing, and if so, how is this fault cleared? Could this just be because the battery is low? Any suggestions?
 
just try putting a jump lead from the alternator body/securing bolts to the battery. see if this helps. i was getting silly stuff come up and put and earth from battery to alternator body. cured the temp rising when lights put on syndrome!!
 
Normally you should have 12V (or battery voltage) on the brown/white wire which would normally come from the ign switch via the ign light. When the alternator is not turning and generating voltage, this is taken to earth (-ve) via the diodes and so the Ign light comes on. As soon as the alternator is generating the voltages equalise, no current flows and the Ign light goes out. From the above, it would appear there is a problem with the Ign light wire (brown/white). However, this is a P38 and nothing's ever that simple. I don't have the info to hand but I suspect it all comes and goes to the BECM i.e. the brown/white charge wire feeds a signal to the BECM which then processes it, decides whether the alternator is doing what it should and switches on/off the ign light and also the 'alternator fault' message on the dash. Probably one for Irish or one of the other BECM experts on here.
What are you getting on the 'W' terminal when the engine is stopped. Do you get any voltage? If not, any circuit to earth? (remember to put the +ve of the test leads to the 'W' terminal).
 
HI Derek, many thanks for the reply, I think your assumption about how the circuit is right from what I have seen on the Rave ETB. I will check the W terminal tonight and report back, I know I had continuity to earth when I tested yesterday but I cant be sure I have the +ve lead of the meter on the W terminal so will check again. I cant believe I'm having so much trouble for a simple alternator swap
 
Ran some checks tonight and this is what I have found.
There is continuity from the brown/yellow wire on W+ terminal from alternator to connection under expansion bottle and continuity from that connection to BECM connection C114 pin 15, and from alternator W+ terminal to BECM cnnection C114 Pin 15 with the connector reseated.
On ignition 2 there is 2.5v to this pin, with engine running there is 14v and 0v with ignition off
Measuring the W+ terminal to battery earth I get 2.5v with ignition at position 2
There is 13.7v - 14v with engine running measuring across the battery terminals.
Running an earth from the alternator mounting point to battery earth made no difference.
I have no battery light and although all readings would indicate that the alternator is charging I dont have enough faith to take the vehicle out.
I again changed the bulb for another known good and still no illumination.
What is left to try, connection from BECM to instrument panel? Which connection wire would be the one to check?
Any ideas?
 
The 2.5V to the alternator from the BECM does not sound correct. I'm off Nigeria at the moment and don't have Rave with me so I can't check. What happens if you earth the brown/white wire now? If still no ign light, then the problem would appear to be in the BECM and I suspect on the input from the alternator rather than the output to the ign light. Having said that though, you mention 'Alternator Fault' warnings on the dash but only when it's been stood. Odd. I have had these though come and go for no apparent reason but usually when just started.
I'm afraid I'm going to have to hand you over to someone on here with more info than I have here. Sorry I can't help you further. Good luck with it and I hope you get it sorted soon.
 
Intend to watch this thread closely as I have exactly the same symptoms. Exactly.

However I can tell you that its safe to drive as I've been driving trouble free for 4 months except for the lack of battery light and the "alternator fault" report if you leave the ignition in 2. My replacement alternator was a 120A unit through Britpart. They were very good when I reported the fault and sent me a new one no problems, but I haven't had time to fit it in (possibly partly because the car is running ok). A friend who is better at electricals than me says the rectifier on the first Britpart one may have had a faulty connection OR not be quite 100% compatible but that since the battery is clearly charging and the car is running, he said it was up to me if I was ok to live with it.
 
Ah-ha! Then that would tend to indicate your BECM is fine and there's a problem with the alternator side. I'm beginning to suspect that some replacement alternators are not quite as compatible as they should be, especially when you read Rasheeds post above. It may well be there is some additional or different circuitry for the ign light in the original alternators that is not present in the aftermarket items. I can't think what else it could be. As Rasheed says, you know it's charging OK so is it something you could live with, if only on a temporary basis, until you sort it properly.
A simple check you could do to see if it's a compatibility thing is to wire a very low wattage bulb (eg one of the ign bulbs you've changed) between the +ve of the battery and the W terminal on the alternator. It should light with the engine not running and go out when the engine starts. If it does this, the alternator is not compatible. If it doesn't go out, there is a definite fault on the alternator and should be returned.
Have you contacted the supplier at all? If you have, what did they say?
Cheers
 
I have not checked RAVE, but normally the warning light is fed with 12 volts when the ignition is switched on, this 12 volt feed goes via the bulb to the alternator and provides the excitation current to kick the alternator off charging. Some alternators have sufficient residual magnetism to start charging without the excitation voltage which is presumably why yours is working.
As you have found that the bulb lights when you ground the wire (at the alternator?) then the fault must be in the alternator which due to either a fault or a design change does not pass enough current to light the bulb.

You could check to see if the alternator charges if you start the engine with the W+ wire disconnected. If it does not charge with the wire disconnected then you could try a very low wattage bulb and re-connect the wire and see if it lights.

Possibly the alternator is not compatable with the P38. there are a number of different alternator types. For example I have one that requires the charge lamp to be connected to earth rather than 12 volts. Obviously an alternator of this type would not provide a circuit to light a lamp connected to 12 volts.
 
HI Derek & Datatek, I shall try the bulb theory tonight and let you know what the results are. From what you both say, it would appear that the alternator is not as compatible as the makers would suggest. The part is supplied by britpart who are normally very good, I shall contact them and see what they have to say.
 
jdennington said:
OK this one has me stumped, my old alternator bearings were getting noisy so I decided to change this before it let me down. Fitted new alternator only to break down on the way to work. RAC ran some checks and reported that diode pack was faulty as there was no charge light showing on the dash and just 11 Volts going to the battery. If the thin brown/white wire connected to the W+ terminal was put to earth, the charge light would illuminate. Another new alternator fitted tonight only for me to find that there is still no charge light showing on the dash. Changed the charge light bulb for know good one, still nothing. Reading on the battery with the engine running gives me 13.7 - 13.9 Volts so appears to be getting a charge. There are only two wires going to the alternator, one large red which will only fit to one terminal and one thin brown/white wire which is going to the W+ terminal. I get a closed circuit to positive if I test the red wire and a closed circuit to earth if I test the brown/white wire. I also get a good earth circuit to the alternator body. The negative terminal of the battery was disconnected for each removal/refit of the altrenators. I get an "ALTERNATOR ERROR" show after a while if I dont start the engine but no error if I do. The test on both wires would seem to suggest that there are no breaks in them. Where else should I check, and would the "ALTERNATOR FAULT" error stop the charge light from showing, and if so, how is this fault cleared? Could this just be because the battery is low? Any suggestions?
Click to expand...

If the bulb is sound charging light malfunction is usually a bad earth.
 
wammers said:
If the bulb is sound charging light malfunction is usually a bad earth.
Click to expand...

The fact that the alternator is charging according to a meter test across the battery eliminates a bad earth as a possible cause of the problem as the earth route is the same for the charge warning light as it is for charging except that the charge warning light circuit to earth is via the regulator/diode pack and the field windings.
 
Datatek said:
The fact that the alternator is charging according to a meter test across the battery eliminates a bad earth as a possible cause of the problem as the earth route is the same for the charge warning light as it is for charging except that the charge warning light circuit to earth is via the regulator/diode pack and the field windings.
Click to expand...

On alternators unless this one is wired differently, if you disregard the main heavy charging leads there is usually a mostly black lightweight cable connected to a small terminal on the alternator, that is the charging light circuit. If you touch that to earth on the engine with ignition on, and the light comes on then there is a bad earth switching route within the control unit. If the light is not coming on at all with engine stopped and ignition on and connected to alternator same fault unless the bulb blown.
 
Last edited:
wammers said:
On alternators unless this one is wired differently, if you disregard the main heavy charging leads there is usually a mostly black lightweight cable connected to a small terminal on the alternator, that is the charging light circuit. If you touch that to earth on the engine with ignition on, and the light comes on then there is a bad earth switching route within the control unit. If the light is not coming on at all with engine stopped and ignition on and connected to alternator same fault unless the bulb blown.
Click to expand...

I would be interested to see an internal wiring diagram of an alternator with a separate earth for the charge light to add to my alternator file.
I have internal diagrams for one wire (no charge light internal excitation) 2 wire (2nd wire is for the charge light/excitation current) 3 wire the third wire is used for remote sensing of battery voltage, 4 wire the 4th wire is an AC output used for the rev counter.
These alternators are all types that have an internal regulator and diode pack. Obviously externally regulated alternators will be different.
 
Just looked a RAVE and, typically the P38 is different!, below is a clip from RAVE about the charge warning light.

Charging System
When the Ignition Switch (X274) is in position II, the
BeCM (Z238) turns the charge warning light on via
the datalink connection to the Instrument Pack
(Z142)
When the Generator (Z106) starts to produce power,
the BeCM (Z238) gets an input signal on Pin 15 and
turns off the charge warning light.
For the Diesel engine this signal is also used as an
input signal for the fuel pump relay inside the Engine
Compartment Fusebox (P125) to make sure that the
Fuel Pump (M109) is only supplied with power when
the engine is running.
If the Generator (Z106) fails to produce power, the
charge warning light remains illuminated.

According to the RAVE wiring diagrams, the alternator is a standard 2 wire unit, the difference being that the charge light circuit is fed via the BECM rather than direct. The BECM turns off the charge light when it detects a change in current flow on the W+ line from the alternator. If the change in current flow is insufficient the BECM will not detect that the alternator is charging and so will not turn off the charge light.

Hope that is of help, typically P38, it takes what should be a simple circuit and adds a layer of unnecessary complication.

If you want circuit diagrams, PM me with an email address and I will try to send them to you. I could not get this forum to accept my RAVE drawings.
 
Datatek said:
Just looked a RAVE and, typically the P38 is different!, below is a clip from RAVE about the charge warning light.

Charging System
When the Ignition Switch (X274) is in position II, the
BeCM (Z238) turns the charge warning light on via
the datalink connection to the Instrument Pack
(Z142)
When the Generator (Z106) starts to produce power,
the BeCM (Z238) gets an input signal on Pin 15 and
turns off the charge warning light.
For the Diesel engine this signal is also used as an
input signal for the fuel pump relay inside the Engine
Compartment Fusebox (P125) to make sure that the
Fuel Pump (M109) is only supplied with power when
the engine is running.
If the Generator (Z106) fails to produce power, the
charge warning light remains illuminated.

According to the RAVE wiring diagrams, the alternator is a standard 2 wire unit, the difference being that the charge light circuit is fed via the BECM rather than direct. The BECM turns off the charge light when it detects a change in current flow on the W+ line from the alternator. If the change in current flow is insufficient the BECM will not detect that the alternator is charging and so will not turn off the charge light.

Hope that is of help, typically P38, it takes what should be a simple circuit and adds a layer of unnecessary complication.

If you want circuit diagrams, PM me with an email address and I will try to send them to you. I could not get this forum to accept my RAVE drawings.
Click to expand...

Ok so the dipsticks at Land Rover have taken what anyone could understand and transformed it into electronic nightmare. But that still does not tell this person why he had a charging light before he fitted his new alternator and why does not have one now. Why do these P38s have to be so complexed? Maybe so the dealers can screw your arse everytime a bulb blows.
 
wammers said:
Ok so the dipsticks at Land Rover have taken what anyone could understand and transformed it into electronic nightmare. But that still does not tell this person why he had a charging light before he fitted his new alternator and why does not have one now. Why do these P38s have to be so complexed? Maybe so the dealers can screw your arse everytime a bulb blows.
Click to expand...

Actually it does tell what the fault is, insufficient voltage/current at the W+ terminal. Either a duff alternator or an incompatable alternator.
 
Datatek said:
Actually it does tell what the fault is, insufficient voltage/current at the W+ terminal. Either a duff alternator or an incompatable alternator.
Click to expand...

We are talking here about a charging light that does not come on at all. Not one that refuses to go out. Duff alternator, that may be a faulty earth circuit in the controller then? As i said earlier, usually the cause of the light not coming on at all is a earth problem unless the bulb is blown. Land Rover P38s seem to use the the circuit from the alternator to tell the Becm to switch the light off on the dash. If as our friend says, when the wire is put to earth the light comes on, then that part of the circuit (the Becm part) seems to be working. What is not working is the standard switching circuit in the alternators controller. It has an earth fault. Which is what i said at the start.
 
wammers said:
We are talking here about a charging light that does not come on at all. Not one that refuses to go out. Duff alternator, that may be a faulty earth circuit in the controller then? As i said earlier, usually the cause of the light not coming on at all is a earth problem unless the bulb is blown. Land Rover P38s seem to use the the circuit from the alternator to tell the Becm to switch the light off on the dash. If as our friend says, when the wire is put to earth the light comes on, then that part of the circuit (the Becm part) seems to be working. What is not working is the standard switching circuit in the alternators controller. It has an earth fault. Which is what i said at the start.
Click to expand...

I agree with you, what I was disputing was your comment about the "little wire usually black" It does not exist on this alternator. the earth is via the electronics in the regulator to the frame of the alternator.
 
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