The MR2 Owner's Club of New Zealand

It's possibly the belt being loose?
MR2s are notorious for eating alternators. I've had 9 failures in 7 different ways over 14 years. First one wore out, second one bust a diode then the third one has had many failure modes. It's now got worn bearings that need replaced.

I suspect mine is down to user failure, I.e dripped some oil while doing an oil change a couple of weeks ago ..

I'm going to do some basic diagnostics tonight when I get home from work.

GDII wrote: ↑

Thu Aug 04, 2022 4:04 pm

It's possibly the belt being loose?
MR2s are notorious for eating alternators. I've had 9 failures in 7 different ways over 14 years. First one wore out, second one bust a diode then the third one has had many failure modes. It's now got worn bearings that need replaced.

Cleaned up a couple of grounds at the rear. Checked the 7.5v fuses fromt and back.

So I charged the battery up to 12.4v ignition off.

Started the car and the voltage drops to 11.9v @1400 rpm.

Revved it a few times no increase in voltage. Put lights on etc and it went down to 11.8x volts.

I wasn't fully able to unplug the 3 pin oval from the alt as I just couldn't get it out to test each pin.

So I'd say having read up on the subject it's 30/70 % either the middle wire or a new alternator time...

I'd say new alternator. 9 out of 10 times it is.

You know what's weird, I charge my car battery to 12.7v (checked with multi meter).

And I leave charger plugged in and I turn on my ignition but don't start the engine.

I get the hotcat sensor light and the battery discharge symbol.

But if the car isn't running, of course the alternator isn't running so why wpuld these lights even come on? Does this indicate a wiring issue somewhere as to my simply mind wouldn't they only be an error when idling due to low voltage?

Those lights go on because the alternator is not charging because the engine is not running. It's normal.
If the engine is running and they are on the alternator is definitely not charging.

Update; new Alternator fitted and problem is now fixed.

Excellent.