Code 48 - Battery voltage low - with new battery!

[Leigh]

Any thoughts on this one folks?

I just fitted a new battery , (the old one was 5-6 years old and not holding a charge anymore, even after 2 nights worth of taking it off the car and putting it on charge , the little charge indicator hydrometer stayed black ).

Prior to changing the battery it had just started intermittently flashing the ECU light, and it had code 48 stored which reads as battery low voltage (it's an 8 valve..)
Checked with multimeter and with it revving over 2000-2500 , the voltage was around 14.5-14.6 volts, so it sounds like the alternator is fine.
The old battery was OK for a couple of days and then yesterday morning it gave up the ghost.

Anyway, with new battery fitted last night, car started first turn of the key, no problems. Drove to work this morning and the ECU light started again, and when I checked the codes at lunchtime it's 48 again....

Any ideas what might be causing it to say low battery voltage? Battery shows 12.5V on the multimeter last night before I fitted it, and the ECU light seems to only come on when the cars pulling/doing some work . Just sitting idle doesn't seem to cause it, but accelerating does. Doesn't seem to be affecting the performance at the moment tho, strangely if anything it seems slightly smoother!
Battery earth points look OK, tho I might need to take another look at the main battery earth lead, as it's a replacement from a scrappies, my original had a badly corroded battery terminal, the replacement has some electrical tape covering the middle, so I'll check why over the w/end (tho it's been on the car for about 2 months or more without any problems..)..

I'm hoping the fact that it only seems to flash the ECU light under load isn't pointing to a failing alternator, tho it sounds plausible So far, no dimly glowing battery light, so I guess the diode packs OK, maybe it's struggling to produce what's required under load, but is fine when just revving in neutral hence it reading at 14.5 when I tested it.

Having just watched that fifth gear clip, he mentions that failing sensors/electronics can be the cause of high emissions - which is what caused me a problem at the recent MOT, I'm wondering if the two are linked..

[Stupink]

probably the alternator... with the car at idle, and switch on everything you can, how low can you get the voltage across the battery to drop? it should start at about your 14.5v while idle, you shoudlnthave to rev it..

you say nodim batt light, but does the batt light come on with ignition and go off with car start?? if not the bulbs gone, hence maybe why you have to rev it to 2,500 to get the charging circuit to engage

[Callyman]

Have you also tried a drain test across the battery?

Remove the earth lead and put a tester between the earth trminal on the battery and the earth lead youve just removed. you should get less than 1 amp as the only thing drawing current should be the clock.

[Leigh]

Cheers for the replies guys
Stupink, the battery light is lit as normal with the ignition on before starting, and goes out once running. I think (brains all foggy at the moment, LOL !) that it was showing 14.5V-14.6V with it at idle anyway, didn't change much when revving it. I haven't done the same tests since fitting the new battery yet, will do over the weekend.

I did the 'switch everything on' type test this evening just as I was about to leave work, tho only looking at the in car volt gauge, will repeat it using the multimeter, but with the fan going on full speed (that always makes it drop slightly), both heated seats, the heated screen , front & rear fogs and headlights on it got down to about 12V from memory...

Callyman, thanks for that as well, likewise I'll test it over the weekend. As you say, should only be the clock, and the trickle for the radio drawing from the battery really.

On the good side, it started first turn of the key , volt gauge in the car was showing the battery at around 13V with ignition on..

[MJ]

I had this once on a cali and eventually traced it to the interior light shorting out onto the roof skin, someone hadnt replaced the plastic cover on the back when changing a bulb and its a constant live to it with a switched earth ... probably not your problem but maybe worth a look.

HTH

[Callyman]

0.1 is less than 1. lol

[Callyman]

Agreed, i put less than 1amp as i cant remember what it's meant to read.
I had a drain on mine last year, turned out to be the diodes in the alternator had blown and used to drain a fully charged battery in 48 hrs.

[Leigh]

OK, update..
Haven't done the drain test yet, that will have to wait till tommorow..

Battery voltage with ignition off was reading 13V (just driven the car for 10 miles or some coming back from g/f's..). That's about what it's been showing before starting the engine ,on the internal gauge since fitting the new battery.

Engine running at idle was 14.5V ish (it's only a £20 multimeter so probably not super acurate..)

Turned both heated seats, rear heated screen, cabin fan to full , headlights on , voltage across the battery was 11.98.
Held the revs att 2500 ish and voltage was 13.

While driving earlier today, when the cooling fan kicks in, on the internal gauge it drops from 14V to about 13.5 while the fan is running.

Should the alternator be able to provide enough juice to charge the battery while running the car even with everything turned on (not likely in the summer , but in winter it's feasible that all of the above would be on for the period of a journey.)

The ECU light has been pretty much consistenly on and off today when driving, any time it's under load like accelerating... Seemed to be OK for the first 5 miles or so, then it started popping on again. Doesn't affect the car as far as I can feel.

[Stupink]

im not sure if the smaller alternators would make full power at idle, but i find it hard to believe they wouldnt at 2.5k revs, and 13v is a bit on the low side.
how many amps is your alternator? perhaps someone else who's cars working atm could offer some comparative readings..

[Leigh]

I don't know of the top of my head what rating my aternator is, never had cause to check it before . I'd guess seeing as it's the ickle baby 8V that it will be the 70AH or whatever the smallest is..

Despite it being all of 5 mins between doing the readings and posting, I'm finding myself not 100% sure of what the readings were! I'll repeat later today with the aid of a brick for the throttle control in place of the g/f

Something tells me (must be that Calibra owner 6th sense..) that I'm gonna need a new alternator, tho I guess it could be the wiring from said alternator to the battery. If it's goosed/corroded to hell it could be losing it with the 'higher' voltages..

[Leigh]

Didn't get a chance yesterday to redo the test or do the drain test,
ECU light on again this morning on drive to work, after about 1.5 miles, noticed that the in-car gauge showed it at 14.5 ish at first, then it gradually dropped slightly,till it was showing just on or slightly under the 14V line. All I had running was the fan on 1st speed, wipers and sidelights (torrential rain on the way to work...).

Car started on first turn of the key again, so at least the batteries holding up (for now..) , obviously I want to sort it in case it's not giving the battery a good charge whilst being driven..

[Leigh]

OK, just nipped out and redid the voltage readings.

Battery (ignition off) : 13V
Idling: 14V
Idling with everything on: 12.6V

Just to add to my "I'm so sick of not having it running right.." mood,
today it's started doing it's "I'm going to cut out when you come to a stop" act again
Last time I thought I'd nailed it with the small hole in the manifold before the O2 sensor, but it doesn't seem to be running rich like it was that time. <sigh>
Oddly tho, only once briefly on the run home did the ECU light come on (yet all the way home it was threatening to cut out whenever coming to a stop at a junction etc, and did once before I caught it ..)

[Stupink]

not good then, see if you can try another in there did you check the amps?

[whippit]

Check and clean your earth Strap

[Leigh]

Nah, not yet Stupink, meant to and forgot again, will have to be tommorow or wednesday after I get back from work I think.

Just so I'm clear in my own head, even at idle should the alternator be able to cover the load AND charge the battery (so in my case it would need to be at least above 13V..)