ABS Light Strange Behaviour

[Mrrnoname]

Hi All,

 

I have a 2003 reg Mk 1 1.9 SDI Skoda Fabia.

 

Two weeks ago I noticed that the car was slow to crank over one morning. Then on my way to work the battery light came on. Garage looked at the car and diagnosed a faulty alternator. Alternator was changed and all was well. Battery light is off when driving and the car cranks over quickly in the morning again.

 

However, now when the car is first started in the morning and the engine is first running the ABS light comes on for about two seconds and then goes off. Reading around this indicates that the battery is bad and can't provide enough volts after cranking, so the car is receiving a false abs issue.

The battery is only about 3 years old and a quality brand. It also spins the engine over really quickly, even first thing in the morning. No sign of struggle at all.

 

Should I be looking at replacing the battery or could my replacement alternator be doing something it shouldn't?

 

I've ordered one of those plug in cigarette socket volt meters to hopefully catch if the volts are dropping low after it first starts.

 

Any advice would be much appreciated!

 

 

Max.

[TMB]

Does the battery light come on just with the ignition on (engine not running)?

[Mrrnoname]

Yes the battery light comes on with ignition but then goes off as soon as the engine is started.

 

The ABS light also comes on with initial ignition but goes off after a second (normal). Then when the engine is started it's back on for two seconds flashing, but goes off quickly. Only happens during the first cold start of the day. If I turn the engine off and repeat the sequence I don't get the ABS light flash once it's running again.

 

What was mentioned in the other thread about the battery being unable to provide enough volts shortly after the high load of a cold start makes sense, but I've never had any trouble with this battery in the three years that it's been installed (it's a Bosch S5), it whips the 1.9 SDI engine over, even when it's sub zero outside. Seeing as I've just had a new alternator fitted it's quite a coincidence.. I was wondering if there is any way that the new alternator could be causing this ABS behaviour. It's not a massive issue I guess as the light goes out within a few seconds. I just get the inkling that something isn't quite right.

 

 

Max.

 

 

 

[TMB]

Hmmm, that's a strange one.

[Mrrnoname]

Yep.

I'm going to plug one of those cigarette socket voltage meters in and see what the voltage is reading when the light is flashing for those few seconds after the cold start. ABS light never comes on during driving though and the new alternator is changing the battery fine so I assume that's working as it should. It's not affecting driving or anything, just odd that the behaviour has changed after 16 years and 170,000 miles 😀. I've become so attuned to the car & engine that any little change / difference is immediately noticed.

 

It's a super car overall though.

 

 

Max.

[Breezy_Pete]

Voltage across battery terminals before and after starting the engine should be useful info.  Measuring at ciggie light socket should be OK, I think, as it's a permanent feed. 

 

Maybe replace all the fuses associated with the ABS system in case one has a bad/resistive contact.  Certainly a good eyeballing of the strip fuse would be wise.

Strip fuse number 6, blade fuse number 7 under the cover to the right of that, and fuse 25 in the cabin fusebox, I think.

 

[vindaloo]

Alternator wiring has been disturbed. Possibly it's cracked/cracking or generally on its way out. 

[Mrrnoname]

Tried something new this morning.

 

Started the car in the morning and the ABS light illuminated when the engine started and remained on for 4 seconds. After it had gone out I stopped the engine and repeated the sequence. This time the abs light stayed on for 2 seconds after the engine had started. I then stopped the engine and repeated the same sequence and this time the abs light stayed on for 1 second. Finally I stopped the engine and repeated the same sequence for the 4th time. This time the ABS light did not illuminate after the engine had started. It will continue to be this way (i.e acting normal) until the next morning. Quite interesting. It's almost as if something is struggling to "wake up" in the morning when it's cold. Incidentally the battery had absolutely no issue starting the car 4 times from cold, each time it spun over really fast and fired right up.

 

ABS light never comes back on during driving.

 

 

Max.

Edited 15 November, 2019 by Mrrnoname

[Mrrnoname]

So after some testing:

 

Resting battery voltage in the morning is 12.7 volts

Voltage dips for a brief moment to 9.5 volts when the car is started (less than a second, but this is when the ABS light comes on)

Car running voltage is 14.4 volts a few seconds after starting

Car running voltage is 13.8 volts with headlights, radio, blowers on full and rear window demister on.

 

Would you expect the voltage to briefly drop to 9.5 volts (less than a second) when the starter is cranked, not sure if this is normal, or if this is what's causing the ABS light to come on? Is 14.4 volts normal for engine running?

 

 

Max.

[Breezy_Pete]

I don't think mine dips that low, but it certainly gets down to 10.5 very briefly. It is a 6 year old battery though, which was in a project car that got very little use for the first two or three of those.  I wonder if your newish battery was damaged rapidly by being deeply discharged when connected to the faulty alternator?

 

A good rule of thumb for alternator output is 14.2 +/- 0.2, because it is quite temperature dependent, putting out a higher voltage the colder it is, lower the warmer it (the alternator) is. 

Your alt appears to be fine, no surprises that the voltage as measured at the ciggie lighter will dip a little lower when there's lots of load going through the wiring into the cabin etc.

 

Is there a battery in a friend's similar car you could borrow to see if substituting that in fixes things?

 

Edited 18 November, 2019 by Wino

[Mrrnoname]

Thanks Wino,

 

That's the next plan, just to see if the light does go back to "normal" with another battery.

 

To be honest though it's causing no issue. I have done 200 miles in the car since in quite a few journeys and after that few seconds in the morning the ABS light never illuminates when the engine is running, so although it's odd behaviour. It's not really a problem. Maybe the discharging of the battery when the alternator was broken caused it to weaken. I'm beginning to suspect the alternator was failing to charge for about a week before I noticed as I remember thinking that my window was slow to move up and down days before the incident, which at the time I put down to the motor becoming worn.

 

[rum4mo]

I think that the only type of volt meter to use to check the voltage at engine cranking is a moving coil type as that type responds to changing voltage far quicker than a DVM, or at least a DIYer's price range DVM. I ended up buying one to check cranking voltage on an Ibiza, initially I checked it using a CTEK charger/tester - but unfortunately that device only operates above 9.? volts so when the cranking voltage dropped near to that it switched off instead of staying on and indicating that the battery had passed or failed that test, very annoying!

 

Surely with the onset of colder weather, that battery in your car will start to give indications of its weakened state.