Can alternator fail without warning lamp coming on?

[Digsy]

I think I have a failed alernator but oddly the charge warning light wasn't the fist symptom.

 

First of all a few days ago my oil level warning light started coming on intermittently. First time it happened obviously I checked the oil and topped it up. Today the symptom developed into the oil level warning light coming on when the engine was at idle, but going out at higher revs. This seemed odd and I even speculated that my oil level and pressure lamps had somehow got wired up the wrong way around.

 

On the way home tonight the oil level warning lamp started coming on at higher and higher revs, until it was on all the time. Having checked my oil again today I knew it was a false alarm so I assumed it was a faulty sensor and carried on.

 

However, a few miles on I started to get a "christmas tree" consisting of:

Oil level warning

Battery warning

ABS warning

Cat temp warning.

 

Next my radio went off, so I decided to turn back. As I went around a roundabout I noticed that my power steering was going light and heavy at random. Also the temp gauge was low and the dashboard lamps started dimming. I just got back to my girlfriend's house before the car died and would not restart.

 

I'm hoping that this is a faulty alternator and the warning lights were a symptom of the general voltage level dropping, but if so why didn't the alternator lamp come on first? Also the car ran absolutely fine until I stopped it myself.

 

For info, crank pulley is fine and as far as I can tell the FEAD belt is not slipping. If I can get it jump started tomorrow I'll do the voltage check to see if the battery is getting charged.

 

Finally, maybe coincidence but a few weeks back I replaced the battery.

[Kopite]

Exactly the same process mine did when the alternator failed. Can't confirm all is well as the car's in pieces still having other bits done

[supra-ireland]

I think I have a failed alernator but oddly the charge warning light wasn't the fist symptom.

 

I've never checked the setup in the Supra but alt charge lights usually work by measuring the potential difference between the battery and the alternator output.

Once the alternator starts to fail and the voltage generated drops the light should come on.

Is the bulb for it working?

If so it sounds like there's a problem with the ECU or something similar.

[Mcgoo]

Loose battery terminal, dud battery maybe.

Admittedly it sound more serious/expensive than that.

 

Hope it's simple and cheap for ya.

[JustGav]

Give a mo, I'll pull the eletrical diagram, but I suspect it is probably just an alternator going pppffffutt.

 

EDIT:

 

No connection to ECU so would say the ecu is probably just throwing the lights because of the undervoltage and nothing to worry about.

 

On the warning light side, you checked the bulb?

 

Edited June 25, 2010 by JustGav (see edit history)

[Digsy]

On the warning light side, you checked the bulb?

 

Yes The battery warning lamp did come on in the end but only when I got the full Christmas tree.

 

Hopefully just an alternator then. Will do the checks today.

 

Cheers!

[w41k3r]

mine did exacly the samei was lucky though the wire on top of the alternator had just come lose easy fix for me try it

[Digsy]

Right-ho, Courtesy of Soop Dogg I have obtained a TT alternator and put it on my car today. The car now runs and shows no sign of conking out BUT the warning lamps that were the first to come on now will not go off. I have permanent oil level warning, catalyst temperature and battery discharge lights on.

 

The car has plenty of oil in it, the cat temp light comes on from cold so that must be a false alarm too. As the car now runs I assume the battery is charging.

 

I'm assuming at this stage that its something to do with the fact I now have a TT alternator on my NA. NA alternators are 90amps. TT's are 90 amps for a manual and 100 amps for an auto (not sure which mine came off).

 

I'm away from my wiring diagrams CD ROM at the moment. Does anyone know if the oil level, cat temp and discharce warning lamps have anything common in their wiring that might have failed? Or could anyone tell me if there are any issues with fitting a TT alternator to an NA?

 

Cheers

[jagman]

As the car now runs I assume the battery is charging.

 

 

better to either measure the voltage or see if headlights get brighter when running as a quick check

[Digsy]

I've been advised to also check the engine ground points which makes some sense because all the sensors that have warning lights on would be grounded through the engine. Can anyone tell me where they are?

 

Its a pain not having my refenece material handy.

[David P]

I have a 100 amp N/A alternator up for sale if you need one.

 

http://www.mkivsupra.net/vbb/showthread.php?p=2805432#post2805432

[JustGav]

I've been advised to also check the engine ground points which makes some sense because all the sensors that have warning lights on would be grounded through the engine. Can anyone tell me where they are?

 

Its a pain not having my refenece material handy.

 

Do you want me to send you all the diagrams, I've got a pdf handy if need be.

 

Gav

[Digsy]

If you could post up the pages with the oil level guage warning and cat temp warning lamps on, plus the location of the engine earth points that would be very handy. Thanks!

 

If I need any more I'll drop you a PM with my e-mail on it.

 

I'm a bit limited what I can do this week, then I'm away for a week on a business trip so if any serious investigation is required I nay not be able to get into it for a fortnight.

[Digsy]

This is turing into a proper pain in the ass

 

After more tests tonight I have satisfied myself that the alternator is NOT charging the battery. Voltage on the B terminal is less than 12V and the headlights do not increase in brightness when the engine is turned on.

 

I checked all the fuses associated with the charging circuit (GAUGE 10A, IGN 7.5A, ALT-S 7.5A and ALT 120A) and none are blown. I have checked the voltage on the three pins connector and all apart from the green/yellow wire have 12V on them. The green/yellow wire has 0.6V on it, which makes sense as when this wire is grounded the discharge warning lamp will come on, which it has.

 

So something is preventing my alternator from charging but I have no idea what it might be. Dodes anyone know what the voltages on the three pin connector should be when the alternator is behaving normally?

[jagman]

sounds like the regulator within the alternator , but the slip rings on the alternators also wear away

Both alternators may be faulty but with different problems such as 1 regulator gone , and one slip rings gone -

You could try swapping the regulator around and check the copper slip rings to see if any material left on them

[jagman]

looks to me that the yel/green wire from the combination cluster is fed from the alt to the oil level indicator via a time delay - ie the oil level can only come on with the engine not running after a delay to allow oil to settle

So the yel /green wire from the reg in the alt has 12v+ with the engine running (thus inhibiting oil level light) no 12 volts engine off

you have 0.6 volts ,eng running so = your problem , with 12v+ (greater than battery volts charge light out, less than bat voltage =charge light on , the more the difference the brighter the charge light

for example bat is 12.1 volts but alt output is 12.05 volts then the red charge light glows

the 12 volts comes from the reg inside the alt with engine running and alt output and yours is 0.6 volts

 

The 12volt from reg again can be considered an engine running signal for the cat warning too so it only comes on with the engine started

hope I make sense

 

Then again I could be wrong

[jagman]

Give a mo, I'll pull the eletrical diagram, but I suspect it is probably just an alternator going pppffffutt.

 

EDIT:

 

No connection to ECU so would say the ecu is probably just throwing the lights because of the undervoltage and nothing to worry about.

 

On the warning light side, you checked the bulb?

 

http://www.mkivsupra.net/vbb/attachment.php?attachmentid=112813&stc=1&d=1277509318

 

from the above diagram

S= SENSE a 12 reference for the alt regulator

L- LAMP a signal (field current) to the warning lamp

B -BATTERY- supply output to battery

IG-IGNITION -self explanatory

[jagman]

http://195.125.241.148/Catalog/Images/IN220.jpg

 

regulator

[Digsy]

looks to me that the yel/green wire from the combination cluster is fed from the alt to the oil level indicator via a time delay - ie the oil level can only come on with the engine not running after a delay to allow oil to settle

So the yel /green wire from the reg in the alt has 12v+ with the engine running (thus inhibiting oil level light) no 12 volts engine off

you have 0.6 volts ,eng running so = your problem , with 12v+ (greater than battery volts charge light out, less than bat voltage =charge light on , the more the difference the brighter the charge light

for example bat is 12.1 volts but alt output is 12.05 volts then the red charge light glows

the 12 volts comes from the reg inside the alt with engine running and alt output and yours is 0.6 volts

 

The 12volt from reg again can be considered an engine running signal for the cat warning too so it only comes on with the engine started

hope I make sense

 

Then again I could be wrong

 

Yeah I see your logic. It depends on what the connection to the combination meter is used for. Either its a 12V signal to say "engine is running and all is well" or its just an alternative ground to allow the lamp to come on so you can check the bulbs when you first turn the key to position 2.

I'll have to study what happens at the other end of the wire to work it out.

As for replacing one dodgy alternator with another....typical eh?

[jagman]

Yeah I see your logic. It depends on what the connection to the combination meter is used for. Either its a 12V signal to say "engine is running and all is well" or its just an alternative ground to allow the lamp to come on so you can check the bulbs when you first turn the key to position 2.

I'll have to study what happens at the other end of the wire to work it out.

As for replacing one dodgy alternator with another....typical eh?

 

The check bulbs function looks to be inhibited unless ;

1 the gear selector is in Park or neutral (auto) or clutch switch (man)

2 the handbrake is selected on

3 the car is not moving -from speed sensor signal

 

Only then you get the bulb test

 

Toyota seem to love their inhibits !!

[Digsy]

Quick update on this.

 

I've had a chance to run some tests and I'm still convinced that the alternator is the root cause of the problem, despite the fact that I've already replaced it with another second hand one. I guess I must have just got unlucky and fitted another knackered part - anyway it was free courtesy of Soop Dogg so nothing ventured, nothing gained!

 

After studying the wiring diagrams of the instrument panel for literally hours I came to the conclusion that they must be either incomplete or wrong as I could not see any way that the charge warning lamp could come on without also lighting the oil level warning lamp. Despite this being my exact symptoms, it seemed too crazy that one warning lamp would also light another, totally non-related one. Note that there is no cat temperature warning lamp on the wiring diagrams that I have so I could not tell if that would also be affected.

 

In order to prove it to myself one way or the other, I went to my car and unplugged the three pole connector from the alternator. Hey presto - the warning lights for charge, oil level and cat temperature went out. I then stuck a pin in the terminal for the green and yellow wire (loom side) and grounded it out to the bodywork. All three warning lights came on.

 

So, bonkers as it may seem, it would appear that while the oil level and cat temp lamps can light independently as they have their own grounds, the charge warning lamp can only come on with these other two lamps, as they share a common ground which is used for the bulb check just before ignition. By studying the wiring diagrams you can see that the check engine lamp is controlled through the ECU and the ABS lamp is controlled by the ABS ECU. The oil pressure lamp is connected directly to the oil pressure sensor. The oil level lamp is connected to the oil level sensor and the alernator, in parallel. I'm guessing it is the same for the cat temp sensor. At key on, all warning lamps will be lit apart from ABS which goes out after the ABS ECU has run its checks, which takes about three seconds. When you key on, the ECU will turn off the check engine light when it is happy that the engine is running properly. The oil pressure light will go out once the oil pump pressurises the system. However, the oil level, cat temp and charge lights are switched off by the alternator cutting the ground on the green and yellow wire.

 

I have a friend who used to have an MR2 on which the alternator kept falling off its mounting bolts. He says that he always got multiple, unrelated warning lights in addition to the charge warning light when this happened.

 

Can anyone else confirm this? It seems crazy for Toyota to save a couple of Yen on the extra wires that would have been necessary in order to get each light working independently, rather than commoning these three circuits together.

 

Anyway, I have a third alternator on the way shortly. Hopefully when I get it fitted that will be the end of this little issue.

[CanisLupus]

When the regulator on mine broke i also only got a Christmas Tree, no charging light or anything else before.

[jagman]

I think you will find that the oil level and cat warning are voltage sensitive so rather than fit a voltage stabalizer or regulator for these two , they just light them up as their warning is now unreliable with lower voltage , ie with no alternator output.

 

The soarer is the same it's cat light comes on with alt failure

[Digsy]

I think you will find that the oil level and cat warning are voltage sensitive so rather than fit a voltage stabalizer or regulator for these two , they just light them up as their warning is now unreliable with lower voltage , ie with no alternator output.

 

You could be right. In the cct diagram the oil level light appears as a variable resistor symbol but in the accompanying blurb it reads more like its a simple float switch. However, the oil level light did come on first when this problem occured.

 

When the regulator on mine broke i also only got a Christmas Tree, no charging light or anything else before.

 

Cool. Cheers

[4packet]

When mine stopped charging it threw up the cat and oil warning too. Replaced the alternator and the issue/lights went away. Had to drive it back from Germany not charging which was fun.