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Driving to work this morning the battery warning light came on and I watched in horror as the voltage went from 10volts down to 8.6 in the space of about 5 minutes forcing me to have to turn off lights/winscreens/stereo/air con/heated seats - not good at 7.00am this morning - in the rain and the cold on the M1

The car was driving fine last night - the battery has been rock solid at around 11.8volts for the past 2 months. The only thing that I did was to turn off the Cobra alarm at the alarm box on Friday evening so it is possible that this has had an effect - anyone got any suggestions as to what the problem might be - Alternator? If so how much are we looking at?
 

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I'm afraid your diagnosis sounds correct, and in actual fact a "constant" reading of 11.8 volts is too low, it should be between about 13.4 and 13.8V, depending upon load, so it looks like it's been on it's way out for a while.

Alternators can be had from as little as about £60 second hand, up to a couple of hunmdred quid new depending upon rating & manufacturer.

I've not changed one myself so wouldn't know exactly how difficult it is as a DIY job but it is fairly well buried under the intake manifold which doesn't bode well...
 

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As Mark says it sounds like the alternator. Before you go down the replacement route check the brush length (should be 5mm or more) and check the earth strap hasn't come loose. If you're lucky your problem will be one of those two. HTH
 

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Alternator prices Ex;Europarts:

9000/cd/cs 2.0 -80A £74.95 88-94
900 4cyl 90A 94-98 £129
900 6cyl 120A 94-98 £165.

these prices are from the 2002 Catalogue,so there could be a slight differance

Fitting costs the usual pint of blood from skinned knuckles but is no harder than most,for best results always do the job out side with the rain running down your back,it also helps if your wife keeps coming out to you and asking how long you are going to be!!
 

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Sounds like the same problem I had with my Volvo 18 months ago. The culprit was the voltage regulator on the back of the alternator (Bosch). This was fixed by the local alternator man who replaced it in situ (2 screws) 15 mins £20. Never missed a beat since then
 

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As a final check before spending any money,
Check all the connections on the charging circuit ie:everything battery terminals/alternator earth straps etc plus have your battery checked! most motor accessory shops will do this for free.
Did the red battery light come on? Do you have a multimeter? if so I could tell you a few checks to do.
 

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I also belive that 13.8V from the alternator when running is too low.

The typical output should exceed 14V.

On the way home today i had 14.1V with the lights and stereo on.

You might want to check the voltage of the battery with the engine stopped, and the voltage when running using a separate multimeter in case the readings you have are inaccurate!

Skiddins
 

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I had problems with the voltage and charging last winter.. Went to the local specialist and had the brushes changed (Cost approx £50) which for a couple of days seemed to work. That is until i made a long journey up the A14 and periodically found the car no longer charging again and therefore effectively sparking off the battery and dying...

After a long and wet wait at the Corley Services and an crafty RAC bodge.. The real culprit was identified as a rusty and therefore intermittent earth connector (Value approx 50 new pence).. Voila car perfect again!

Frustrated that i had taken it into the garage to be fixed already, i asked the RAC chap "so ill be able to get it back to the garage then?" He said "No its fixed.." Doh!!

Worth the RAC subscription alone i reckon!
 

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I also belive that 13.8V from the alternator when running is too low.

The typical output should exceed 14V[/b]
Do any of you electrically minded guys out there know what voltage the display should show when car is running. My two CSs both show around 13.8 to 14.1v which I thought was spot on.
Sis's car drops to 13.3v after 5 mins or so and with everything switched on can get to 12.9v - I assume that this is too low and I should change the alternator - any thoughts?
 

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All of mine run about 13.8v too, except the carlsson that runs barely 13.3v, sometimes down too 12.9v.

The previous owners had a new starters, alternater's and batteries for 4 years before I got it, I've done nothing other that tighten the +ve battery clamp once in 2 years.

I have been a bit worried this last few weeks though when the starting voltage has been down to about 8.7v-9.7v.

Andrew
 

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Sorry, I should have said that the dash meters are a pretty innaccurate representation of the battery terminal voltage; I reckon the tolerance on them is at least +/- 0.2V.

IIRC correctly the terminal voltage on idle, no load, under charge is circa 14.1V. Both my 9Ks have never shown above 13.8V on the dash though.

As a detailed analysis tool for telling you the real state of you battery and charging system, I'd trust the dash display about as far as I coudl throw an Aero armchair... however it is useful for identifying trends- like if it suddenly starts reading much lower or varying a lot (note for Adrian).

You should have been experiencing lower readings lately in the cold weather (note for Andrew), especially on start up because that will have increased the battery internal resisitance whilst decreasing the resisitance of pretty much everything else.

Don't forget, it's not unusual to need to replace your battery after 3-4 years, depending upon usage.
 

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I am with you on this bubbles
all of my 9000's have run about 13.4-13.7 and I have had zero probs with non or low charging (except when the serpentine belt broke
)
and I typically see less than 10 v on start up even with a brand new battery...
 

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Ive posted about electrical gremlins....as a side note it still aint fixed........!!
I drop to 10-11v at start up, running with lights aircon etc on...12.9-13.3v.
running with no lights, no aircon etc...14-14.3v.
Also...I find that I can get variations between 13.1 and 13.9v whilst driving under load......just put new battery on.
 

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Mines being showing 14V when theres no draw on the circuit. However, with the heating fan on full, the headlights on and the radio drowning out the din of the fan the voltage is reading around 13.2 - 13.4 and it does fluctuate slightly with engine speed.

Before I replaced the faulty headlamp wiper I was getting a massive voltage drop at times accompanied by the battery warning light appearing. Since I replaced the wiper motor this had ceased happening and the voltage hasn't dropped below 13.2.

I know my alternators very rattly though and probably in need of exchange or refurbishment? I think.
 

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I get 14.3V with nothing switched on, and using a decent Flike multimeter (admittedly not calibrated for 3 years) it measures 14.42V at the terminals when running.

On start up the voltage drops to about 9.7V.

I'll measure later on tonight under load with stereo, heated seats, lights & ACC etc all running while driving normally....Though i may have to give the multimeter test a miss while moving!

Don't forget that it is POWER (Watts) that allows all the bits to work. Although you may discover that when you car shows a lower voltage this may mean it isn't producing enough current as well as volts

Power (Watts) = Volts * Amps

Skiddins
 
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