Battery Diagnostic LED

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paulh53

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Don't ever trust the little "Diagnostic" LED on your car battery :roll:

Our Peugeot 306 Diesel developed a sluggish starting problem, So I Checked the battery connections etc, And they where ok,
The little green "Diagnosic" LED which is built into the battery was illuminated showing that the battery was fully charged,
The next step with diesel engines is to fit new "Glow Plugs", which we did :? But it still very sluggish starting :roll: We took the car to the garage to have the starter motor checked out, It proved to be ok :cry:
The garage discovered that the battery was duff (Despite the little green diagnostic LED showing that it was Ok)

This Green "Diagnostic" LED had totally misled me in my fault finding ways,
Don't Trust The Little Green Man In Your Battery :twisted: :roll: :twisted:
 
I've never heard of one of those LEDs on battery. New glow plugs wasn't a good decision though, slow cranking wouldn't be that. A multi-meter is useful then you can check battery voltage and alternator charging, available for less than a tenner.
 
Apart from the battery, One of the main reasons a diesel engine is sluggish to start in cold weather is (two or more) faulty glow plugs,

The "Diagnostic" LED is inside the battery, Not on it,

A duff battery can still give out 12v, But won't give much current,

I have three multimeters,
 
Agree sluggish starting can indicate glow plug problem, but I said slow cranking which is low battery voltage, assuming starter and wiring is ok. As your battery was duff then the cranking speed would have been slow. If you are only reading 12volts then battery is discharged. If you put voltmeter across battery in morning you should see at least 12.5 volts and preferably a bit more for a good battery.
 
In all fairness to shaggy you haven't given the best description Paul.

The green glow(inside of maybe, but viewed from on top of the battery) is not a true diagnostic light, it is only an indication that its charged, any battery showing only 12v is probably on its way out.

Most people would assume sluggish means turning over slowly, which could indeed mean the battery or starter or connections including any chassis earths or even other charging problems.

Sluggish may also mean its turning over fine, but not firing, which probably would be glow the plugs or other problems as you said.

I just can't undertand why, given that you have a multimeter and know how to use it, that you chose to take any notice of little green lights. How come you didn't use the meter whilst turning the engine over, to test the battery under load? You could also have used your meter on the glow plugs to save you work and cost.
 
Soz....Won't be so incompetant again :( :oops: :(

Now calling the wife for a severe leg slapping,
 
New glow plugs certainly wouldn't have hurt. Wouldn't counteract a bad battery, but it means that you should have a shorter wait for them to preheat and possibly a shorter cranking time before the engine fires in earnest.

I've noticed a couple of people round here have found the recent cold weather really making their cars' tired batteries obvious. Even made me wonder if I should consider replacing mine in the next few months (car will be 4 years old in July, and most runs I do are about 4 miles).

I bet something like an Optima battery would get your car started in about two revolutions of the starter motor!

Isn't a car battery actually about 14V? Or is that just what the alternator outputs?
 
If buying a battery -- buy a good 'un !! Less is a waste of dosh ..
Only ever bought two batteries years ago, both Exide 'heavy duty' ... never a problem after both purchases ... Quality has a 'feel good' factor, a nice built in extra.
:wink:
 
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