Alternator Over-voltage issue

[ScottAU]

TL/DRAfter approx 30 mins of idle or 1 hour driving time, the voltage output from the alternator rises to above 16v, and causes the electronics to shut down. Have replaced the alternator twice. Battery has been checked.

The Long Story
I'm having trouble with the alternator in my Discovery 3, 4.4 V8 petrol. I've already found lots of useful information on other threads which has got me this far, but nothing that specifically addresses the issue I'm having.


I drove through some very deep mud in Chichester State Forest which packed into the alternator on my disco 3. I didnt receive any battery or warning lights until about 40 mins after the incident, at which point my crank battery was pretty much dead. Being a fair distance from anything i had to bridge across to the second battery to provided enough power to maintain the engine (but not really any of the electronics), and with a couple of jump starts was able to make it out of the forest in 1 wheel drive and get towed to a mechanic.


A new OEM alternator was fitted and I was able to drive 6 hours home to the Gold Coast without any issue.


Over the next few weeks the car wasn't used at all. Then i used it for a few short journeys and started to have issues when the engine Revs exceeded about 3000 - at this point the alternator output would jump instantly from approx 14.5 to 16+ volts causing all of the electronics in the car turn off until the voltage dropped to an appropriate level.


Thinking the issue was related to the alternator or regulator, i took the car to my usual mechanic, and had a genuine Denso Alternator fitted. The mechanic noted that the harness connector (C0053) was badly damaged and would need to be replaced, and that a poor connection could have been the cause of the voltage issues - but they could not get hold of a replacement part. I collected the car with the new alternator (also new belts and tensioners), but with the damaged harness connector still attached.


I managed a few short drives without any noticeable issues, but on a longer drive to Brisbane, the voltage again spiked and caused the electronic shutdown. At this point, and knowing about the damaged harness connector, I located the part locally and replaced it at the roadside. A 10 minute drive later, same issue, and a flat bed to get the car home.


Whilst waiting for the tow from Brisbane i hooked up the multimeter a couple of times and started the engine. Slightly different behaviour - Initially the voltage output would be around 13.5v, and very stable. Gradually over the next 10 mins, it would slowly increase, 13.6, 13.7, 13.8...etc, and as it increases, the speed of the rise accelerated, 14.5, 14.7, 15..... until i shut the engine off to prevent damage. When restarting the engine within 20 seconds the voltage resumes where it left off. If leaving the engine off longer the voltage will begin lower, but quickly rise. The longer the car is left, the lower the initial voltage, and the longer till failure.


It has now been home for 10 days or so (there's no garages open over Christmas), and I've tried a number of things:


- Check and cleaned the earth point under wheel arch beside the alternator
- Checked and cleaned earth points at fuse box
- Checked and cleaned ambient air temperature sensor
- Double checked and cleaned B+ terminal on alternator
- Double checked and re-wired harness connector
- Checked F20 5w fuse in fuse box (see below)
- Removed Dual battery setup to eliminate this as a cause
- Had the crank battery load tested twice and checked for bad cells.


The 5w Alternator fuse in the engine bay fuse box is not blown. When measuring the voltage accross the fuse, it is consistent with the alternator output. However, removing the 5w fuse does not cause any warning light on the dash as suggested below. The engine can be started without issue with this fuse removed.156643


Running the engine with either the ALT CON, or ALT MON connections disconnected causes the battery light on the dash to illuminate, and the Generator Field Circuit error code to trigger. The alternator and voltage regulator in this situation function as described below, with the alternator outputting a consistent and stable 14 volts.156644


Given the above information i would like to assume that the alternator itself is not the issue, and until everything else has been investigated, i would like to assume that the ECM is also not the issue. Knowing that the ECM dictates the voltage set level for the alternator based on various information it is receiving (temperatures, load, idle speed etc...), I anticipate that one of these data streams is feeding the ECM bad information, and given that the issue does not present itself until the engine has run for a short period of time, i suspect it is either a battery voltage sensor, or a temperature sensor.


However, i can't find any information on which data streams specifically the ECU is using to base the voltage set level of the alternator. Any help on this (or other suggestions) would be greatly appreciated.

[theelms66]

I would check external voltage sense terminal whilst engine running . When its behaving and when its playing up. As a poor connection or low voltage at this point would increase charge rate . I THINK.

[Graeme]

Is a battery monitor fitted to the positive or negative terminal of the battery?

[ScottAU]

Is a battery monitor fitted to the positive or negative terminal of the battery?

I usually have the Traxide system installed. However, at the moment i have the second battery removed (and both terminals isolated), and dual battery isolator disconnected from the positive terminal of the main battery (also isolated with insulation tape) for the purpose of troubleshooting.

Other than this, i do not have anything third party connected to the main battery.

[DiscoJeffster]

When I removed my alternator I had a lot of trouble getting the rear wire connector unplugged which I understand is the wire that drives the required alternator voltage. It wouldn’t surprise me if this plug is damaged though the behaviour is odd.

[ScottAU]

When I removed my alternator I had a lot of trouble getting the rear wire connector unplugged which I understand is the wire that drives the required alternator voltage. It wouldn’t surprise me if this plug is damaged though the behaviour is odd.

I have replaced the connector with a new one, so I don’t believe this to be the issue. The old one was completely destroyed (below).156659

[Graeme]

Sorry, I was referring to original fitment although I suspect that no battery monitoring device was fitted to D3s.

[josh.huber]

The body control module should control the voltage from the alternator.
Do you have a scan tool? Gap or similar. Does the voltage on the scan tool match that of the multimeter on the battery.
If you had a bad connection to the module that controls battery voltage this would spike your battery voltage.
Also if you have a scan tool. Reset your battery. If not the alternator might be trying to "boost" the battery back to life. Mine did this. Was over 15 volts on a down hill run. Way to high for a good battery. Are you sure you got the wiring right? I commentated on a post a long time ago where the owner replaced that same plug and wired it wrong. Was easy to do. The schematic he followed wasn't 1, 2 , 3 was 1 , 3 , 2 and caught him out. Ill find it

[Graeme]

The 5w Alternator fuse in the engine bay fuse box is not blown. When measuring the voltage accross the fuse, it is consistent with the alternator output. However, removing the 5w fuse does not cause any warning light on the dash as suggested below. The engine can be started without issue with this fuse removed.Are you saying that you measured the voltage across the fuse pins or between the fuse and earth? If you detected voltage across the fuse pins then the fuse is blown.

[josh.huber]

Alternator Wiring Harness troubles
Alternator Wiring Harness troubles (https://www.aulro.com/afvb/l319-discovery-3-and-4-a/269201-alternator-wiring-harness-troubles.html)

[ScottAU]

156664
Alternator Wiring Harness troubles
Alternator Wiring Harness troubles (https://www.aulro.com/afvb/l319-discovery-3-and-4-a/269201-alternator-wiring-harness-troubles.html)

Thanks, i had already seen your previous post. It the pin numbering on the wiring diagram almost caught me out too, although my symptoms do sound similar to the issues in the other thread - I’m certain it is wired correctly.

Here’s some of the information i found which helped me out with the wiring - it might help someone in future.

156663


156661156662

[ScottAU]

The body control module should control the voltage from the alternator.
Do you have a scan tool? Gap or similar. Does the voltage on the scan tool match that of the multimeter on the battery.
If you had a bad connection to the module that controls battery voltage this would spike your battery voltage.
Also if you have a scan tool. Reset your battery. If not the alternator might be trying to "boost" the battery back to life. Mine did this. Was over 15 volts on a down hill run. Way to high for a good battery. Are you sure you got the wiring right? I commentated on a post a long time ago where the owner replaced that same plug and wired it wrong. Was easy to do. The schematic he followed wasn't 1, 2 , 3 was 1 , 3 , 2 and caught him out. Ill find it

I have a scan tool. All of the relevant voltages on the tool look consistent with the multimeter on the battery.

I guess this means that the ECU/ECM knows that the voltage on the battery terminals is exceeding 15v.

Once the voltage becomes excessive, the first noticeable thing is a flickering of the instrument panel backlighting (noticeable at night only), followed by the shutdown of the media amplifier (although the head unit controls continue to act as normal), after this the Transmission usually faults (with an excess voltage error code), and then all the other control modules seem to fault simultaneously following this, lastly followed by the ECM, at which point, everything electronic stops.

[josh.huber]

Can you or did you do a battery reset?

[ScottAU]

Can you or did you do a battery reset?

A couple of mentions of this. I have not done a battery reset.

Ive seen that the D4 has the battery monitoring system, but i cant find any mention of it for the earlier model year D3s.

[josh.huber]

Yeah I'm notup to date enough with this on d3's to know that. I didn't read the D3 bit. I know it made a big difference on my D4 .

Have you got a photo of the of new pig tail before you joined it into they harness. Has the as pin 1 got battery voltage before the car starts and does it have battery voltage once the car is running.

Did you bare back plenty of wire before crimping those red joiners in?

Paper clips make good tools into those harness plugs .

Where are you, I seen Chichester. Send us a pm you might not be that far away

[ScottAU]

Have you got a photo of the of new pig tail before you joined it into they harness. Has the as pin 1 got battery voltage before the car starts and does it have battery voltage once the car is running.

I don’t have a photo, but checked it lots of times. Pin 1 is the bat sense and has power both before and after starting the engine. Power is lost when removing the F20E 5w fuse.



Did you bare back plenty of wire before crimping those red joiners in?

Yes. I’ve also cut off the connections and reconnected just to be sure. Today I ran a continuity test from the alternator connector to the ECM harness connector for both PWM wires and didn’t find issues.



Where are you, I seen Chichester. Send us a pm you might not be that far away

I'm on the Gold Coast. But the issue began with my drowning the alternator at Chichester. Thanks a lot for the offer though, it’s driving me crazy.

[josh.huber]

You need to measure the power at pin 2 with it running to see what the ECM is commanding.

[josh.huber]

So you have the factory Brown wire crimped into the terminal furthest away from the main battery cable?

[ScottAU]

So you have the factory Brown wire crimped into the terminal furthest away from the main battery cable?

yes. Then the red/white in the centre.

[ScottAU]

You need to measure the power at pin 2 with it running to see what the ECM is commanding.

Hi Josh. I’ll be honest, I’m not an electrician, Please can you explain this?

My understanding is that the two control wires to the ECU work on a PWM/CANbus system, so measuring the voltage shouldn’t provide any clues? If I was to measure this, I imagine that i would have to measure across two ends of the wire, and not to an earth point?

i have checked for continuity from the connector at the alternator to the ECM connector and found no issues. When connected up correctly, I get no error codes, but if I break continuity on either the Control or Monitor wire, I get the alternator light and error codes. This makes me think the ecu is communicating correctly with the alternator.

Does my thinking sound right?

[ScottAU]

Noticed something else whilst troubleshooting yesterday.

From a cold start, initially the voltage output of the alternator is 14.6-14.8, and regulates well when revving the engine, or adding electrical load.

Once warm having idled for 15mins in the driveway the alternator still outputs approx 14.8v. It’s higher than I would expect with a fully charged battery. When I rev the engine now however, the voltage fails to regulate and spikes to 15.5-16.5v.


If I turn on both the headlights and AC, the voltage initially drops into the 13v range, but then a few seconds later resettles at approx 14.8v. Revving the engine now, with the increased demand, the voltage is much better regulated, and will only raise to 14.9v or so.


After driving the car for 30 mins or so, this isn’t the case, and high revs regardless of electrical load from accessories causes a jump into the high 15v to mid 16v range.

[josh.huber]

It's not a V6 petrol alternator is it? They have a different pin configuration.

[josh.huber]

Hi Josh. I’ll be honest, I’m not an electrician, Please can you explain this?

My understanding is that the two control wires to the ECU work on a PWM/CANbus system, so measuring the voltage shouldn’t provide any clues? If I was to measure this, I imagine that i would have to measure across two ends of the wire, and not to an earth point?

i have checked for continuity from the connector at the alternator to the ECM connector and found no issues. When connected up correctly, I get no error codes, but if I break continuity on either the Control or Monitor wire, I get the alternator light and error codes. This makes me think the ecu is communicating correctly with the alternator.

Does my thinking sound right?

Yeah they are pwm from what I've read.

You measure between the wire and earth.

If your multimeter has a pwm mode put it on. However if you just set it to normal volts you will get an idea of what's going on. Just need to look at alt control. Not monitor

[ScottAU]

Yeah they are pwm from what I've read.

You measure between the wire and earth.

If your multimeter has a pwm mode put it on. However if you just set it to normal volts you will get an idea of what's going on. Just need to look at alt control. Not monitor

awesome. I’ll try that. Do you know what a reasonable voltage reading would be?

[DiscoMick]

Been reading this with interest, as I know nothing about D3s, so learning a lot.
On your last question, all I can say is my very non-smart Defender just sits on 14 volts continuously. Would that be a normal start up with a smart alternator?

[theelms66]

awesome. I’ll try that. Do you know what a reasonable voltage reading would be?I think you will need an oscilloscope to check PWM

[DiscoJeffster]

I think you will need an oscilloscope to check PWM

Absolutely. The voltmeter will give the average of the voltage it sees based on the pulses but this means very little in troubleshooting in all reality.

[BradC]

Absolutely. The voltmeter will give the average of the voltage it sees based on the pulses but this means very little in troubleshooting in all reality.

Yes and no. Different meters will give different readings on the same PWM signal, but if you get some baselines like "when it's making 14.5V it reads this, and when it's making 15.6v it reads that" you can get an idea as to what it's doing. Even just watching it vary can be illuminating.

The biggest issue is getting a handle on what your meter does and how it does it.

From what I've been able to ascertain the signals are :
- ECM to alternator, "wind the wick up a bit and give me xx volts please"
- Alternator to ECM, "this is how approximately much current I'm making (or to put it another way, my current load) at the voltage you've asked me to make".

I'd be more interested to see what the alternator does with the PWM input both open circuit and shorted to ground. Those would both be more likely than the ECM doing something funny.

[ScottAU]

On your last question, all I can say is my very non-smart Defender just sits on 14 volts continuously.

If I break the connection on either the control wire or the monitor wire, the ‘smart regulator’ will revert to being a ‘dumb’ regulator and output a constant 14v. The only negative to this that I can tell is the battery light on the dash - so I’m very tempted to run in this configuration for the time being until I’ve found a proper solution.

[ScottAU]

"I'd be more interested to see what the alternator does with the PWM input both open circuit and shorted to ground. Those would both be more likely than the ECM doing something funny.

Thanks for your input.

By open circuit you mean not connected to anything? if so then the regulator behaves as expected (from this document) and outputs a steady 14v

I suspect the same will be the case when grounded, but I’ll have to double check.

EDIT:
The voltage through the control wire to ground is approx 6.8v. This rises to 7.6 as the alternator output rose from 13.8 - 14.8v (alternator output inferred from control module voltage measured with gap tool). There was no error lights on the dash, so suspect the regulator was behaving on usual instruction from ECM.

[josh.huber]

Thanks for your input.

By open circuit you mean not connected to anything? if so then the regulator behaves as expected (from this document) and outputs a steady 14v

I suspect the same will be the case when grounded, but I’ll have to double check.

EDIT:
The voltage through the control wire to ground is approx 6.8v. This rises to 7.6 as the alternator output rose from 13.8 - 14.8v (alternator output inferred from control module voltage measured with gap tool). There was no error lights on the dash, so suspect the regulator was behaving on usual instruction from ECM.

Mmm. Well it seems to all be working and connected. If you have a gap tool like you said maybe you could try and reflash the body control module. Do the d3's have the negative terminal with the amp metre built in. Are you getting a reading for the current at the battery.

[BradC]

The voltage through the control wire to ground is approx 6.8v. This rises to 7.6 as the alternator output rose from 13.8 - 14.8v (alternator output inferred from control module voltage measured with gap tool). There was no error lights on the dash, so suspect the regulator was behaving on usual instruction from ECM.

Awesome. Now you have a baseline to work with. See what it does when it's misbehaving.

[Simo74]

Hi,
Ur disco is basically telling u that the battery is knackered, hence the 16v.
I suggest u sack ur auto sparky and get a competent one. A very simple thing to remember regarding alternators, the lower the voltage the higher the output amps, the higher the voltage the lower the output amps. This is ecm controlled in ur disco and the ecm is asking for minimum amps and protecting the vehicle from a knackered battery when the over voltage is sensed.
A new battery will immediately be able to correctly load the alternator and will cure the higher than 14.8v readings. A load check on the old batteries will show the same result is knackered battery.

[josh.huber]

Agreed that dead battery's do cause issues. But the BCM should be backing the alternator off before it shuts down the car.
He said he's already load tested the battery twice. I'm not sure on a D3 but the D4 can definately monitor current and voltage.

Does it start well everytime? Does it give low battery warnings? What's the battery voltage after it's been sitting for a while and the car is asleep? Can you put the multimeter on and see what the voltage is during cranking aswell?

[ScottAU]

Does it start well everytime? Does it give low battery warnings? What's the battery voltage after it's been sitting for a while and the car is asleep? Can you put the multimeter on and see what the voltage is during cranking aswell?

Starts just like it has for the last 3 years without problem. No battery warnings or battery related error codes (other than when high voltage shuts down ECM, in which case I get multiple associated error codes, but only the transmission reports high voltage). Voltage holds well, when I returned to the car this morning it was 12.9v. Haven’t noticed any major drop off during cranking, but I’ll check that again tomorrow.

156784
Looking at the DCT codes in the attached manual it looks like there is several error codes which can be thrown up by the alternator and charging system. It would be interesting to know which sensors are responsible for determining the above faults, and their parameters.
P1146, P1244, P163, P2504

[josh.huber]

Starts just like it has for the last 3 years without problem. No battery warnings or battery related error codes (other than when high voltage shuts down ECM, in which case I get multiple associated error codes, but only the transmission reports high voltage). Voltage holds well, when I returned to the car this morning it was 12.9v. Haven’t noticed any major drop off during cranking, but I’ll check that again tomorrow.

156784
Looking at the DCT codes in the attached manual it looks like there is several error codes which can be thrown up by the alternator and charging system. It would be interesting to know which sensors are responsible for determining the above faults, and their parameters.
P1146, P1244, P163, P2504

The ECM itself would be monitoring those. No external sensors.

[ScottAU]

Hi,
Ur disco is basically telling u that the battery is knackered, hence the 16v.
I suggest u sack ur auto sparky and get a competent one. A very simple thing to remember regarding alternators, the lower the voltage the higher the output amps, the higher the voltage the lower the output amps. This is ecm controlled in ur disco and the ecm is asking for minimum amps and protecting the vehicle from a knackered battery when the over voltage is sensed.
A new battery will immediately be able to correctly load the alternator and will cure the higher than 14.8v readings. A load check on the old batteries will show the same result is knackered battery.

Put a new battery in today (Varta g14) and it didn't make any difference sorry.

[BradC]

Put a new battery in today (Varta g14) and it didn't make any difference sorry.

Have you had a chance to look at the PWM control line while the voltage is through the roof?

In cases like this I tend to run a small multi-core cable through the firewall and sit a meter/logger/cro (as required) on the passenger seat so I can actually catch it in the act.
It's usually pretty easy as when I'm chasing a fault my wife will refuse to go near the vehicle, so the passenger seat makes a great diagnostic bay.

Seeing as you have a GAP. In the section with extended info (don't have mine handy, but it's not the first "tested" items), do you have an element for requested or commanded alternator voltage?
I have that on the TDV6, and while it bears only a vague resemblance to the actual voltage, the battery voltage does indeed go up and down as the reported figure goes up and down. Just while it's saying the ECU is requesting 15.1V I actually see mid 14's and down from there.

edit : found it
156862

[rusty05]

So what ended up being the issue

[powertech]

Hello!

Is there any solution for this Problem?

Greets

[shack]

Hello!

Is there any solution for this Problem?

GreetsJust to be clear, what is YOUR problem and vehicle details?