R53 2002 - The other day I went for a drive and my Battery light came on. So I turned around to head home and the light went out for awhile and then came back on intermittently. This repeated all the way home, about 5 miles. With the car idling and Battery light ON I put my voltmeter between the under hood + battery terminal and ground and to my surprise the alternator was still charging. The voltage oscillated quickly between 14.15V and 14.24V. What the hell? I waited for the battery light to go out and now the charge is a solid 14.38 volts. Since the battery was 6 years old and showing signs of weakness in the cold I replaced it just to rule out the battery. (New battery voltage with car off is 12.6V.) Same issue. I don't get it. I thought the battery light being ON would indicate no charging. I'm afraid to drive the car any distance. PS this is a heat-related issue. The warmer it is outside, the sooner the Battery light will come on. It was real cold this morning and it took 3 times as long for the light to come on. Any ideas?

 

Some possibilities
>alternator - will need the belt removal tool and to haul it out in 'front end service mode' and have it checked at an electrical place or auto parts store like O'Reilly, Autozone etc. Also check connector / wire lead for corrosion, fraying, insulation failure points etc.
>belt worn, stretched / slipping
>belt tensioner / pulley worn
>idler pulley going bad, starting to seize and cause belt issues
>crank pulley going bad - notorious to the point of inevitability for these cars. The internal vulcanized rubber likes to separate after a time. Symptoms vary but charging issues can be an early one because of belt drive slippage. The end state is limp mode / P1688 OBD2 code / AAA truck home. Most replace it with an ATI or SFI/PRW aftermarket model; not cheap but you'll only do it once. OEM will just reset the clock and you'll face the issue again some day. Mine went at ~50K.

Would remove belt, spin & shake all pulleys including the crank. Should turn smoothly, effortlessly and noiselessly with no 'rattle factor' (axial or radial movement). Would have the alternator checked at an auto parts store and replace the belt regardless, and even if it's good (for now) swap out the crank pulley if you can swing it.

Pelican Parts website has some pretty good visual tutorials also Mod MINI on YouTube. Also recommend get a copy of the Haynes and/or Bentley MINI repair manuals if you don't have one already; a must-have for the torque specs alone.

Link to the tool available in other places too:


Good luck and please let us know how it goes.

 

Separating crank pulley , Slipping belt or failed alternator voltage regulator...