Charging system fault threshold

[Grayfox]

hey

This evening my mums ford focus failed to start.
When i cranked it the starter motor made a rapid click sound, so i got my multimeter and did a basic load test.

Battery voltage under no load was 11.84v and during crank it dropped down to 6.5 which basically said to me a screwed battery.

My main concern is when i did the same test last week(due to the car taking more than 2 seconds to start) the charging voltage was 13.8v across the terminals when it did start at a 1100rpm idle(it was a cold start, but not the first start of the day).

At first i thought this was due to minor corrosion lowering it but if it was not caused by corrosion but was the alternators actual output shouldn’t the charging system fault light be on or when does it light up?

My parents said they had no red or yellow lights on the dash while driving.

The only code that was in the ECU was a P2122 was Throttle/Pedal Position Sensor/Switch D Circuit Low Input, but no others.

Topic

[college man]

What year and engine is your mums car? The light may
not come on when a low or dead crank happens. The light
will come on when running charging voltage drops to a
low point. 🙂

[Grayfox]

2010 model
2.0liter petrol

I did another test on the alternator.

I cleaned the terminals, put my cars battery in.
Car started straight way
The car was getting 13.75~13.82v on idle(900rpm), i raised the RPM to 3,000 still got the same output of 13.8, i turned on the headlights and highbeams the voltage dropped down to 13.4v then went back up to 13.8v.

I did a quick parasitic draw test on the car.
When i connected my multimeter it was at 1.02A for 1 second then dropped down to 700mA.
Which may seems high but on my mums car the radio and onboard computer backlight stay on for a few minutes after the doors close.

[college man]

Sounds pretty normal. I believe the battery was the issue.

[Grayfox]

Thought normal output voltage for an alternator was above 14.0v.
My civic does 14.2v and it has a 1.8(but then again it is packed with gadgets.)

I think 2 cells were dead.

When i connected a 55w H1 bulb the voltage went from 12.1 down to 8.6v.
Battery is only 3 years old.
Piece of crap

[college man]

13.5-14v is normal. The average life span of a battery
is 4 years 🙁 I had a optima red top.Paid 200. bucks.
had a four year warranty. a week later after the four
years it just died. No warnings nothing. never again for
optima.I bought a Walmart battery for 75.00 3.5 years later
still going strong.

[EricTheCarGuy]

Sounds like you’ve got it solved. Battery connections are responsible for a bunch of issues. I even made a video about it.

Looking at your numbers after the cleaning, I’d say you nailed the problem. Keep us posted if it comes back.

[Author]

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