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Lexus IS250 Alternator replaced. Red battery light still on.

  • 26-01-2021 4:36pm
    #1
    Alanstrainor
    Registered Users, Registered Users 2 Posts: 23,157 ✭✭✭✭


    Hey guys,

    So I had my alternator die before Christmas and I replaced it with an equivalent spec unit then and got the car running. After replacing, I fully charged the battery indoors and put it back in the car. I've covered maybe 100km in it since then with no apparent issues, car starts every time and no sign of battery trouble. But the red battery light/charging light remains on.

    Just after turning the car on from cold I get 14.2v across the battery. Which shows that the alternator is charging (at least that is my conclusion). The battery is reading somewhere around 12.3 volts in the mornings before start. Which is a bit low, and I have seen it lower in the last few weeks. But it had been started a stopped without driving a good bit. After a drive it will sit at 12.8v immediately after turning the car off. And obviously read lower come morning.

    Not wanting to throw parts at this to stumble on a fix, does anyone have any clues or ideas for further investigation? I have a battery on order in Halfords which I am probably going to buy at this point, but I don't have much hope for it fixing the problem.


Comments

  • #2
    RandomViewer
    Registered Users, Registered Users 2 Posts: 6,191 ✭✭✭RandomViewer


    Alanstrainor wrote: »
    Hey guys,

    So I had my alternator die before Christmas and I replaced it with an equivalent spec unit then and got the car running. After replacing, I fully charged the battery indoors and put it back in the car. I've covered maybe 100km in it since then with no apparent issues, car starts every time and no sign of battery trouble. But the red battery light/charging light remains on.

    Just after turning the car on from cold I get 14.2v across the battery. Which shows that the alternator is charging (at least that is my conclusion). The battery is reading somewhere around 12.3 volts in the mornings before start. Which is a bit low, and I have seen it lower in the last few weeks. But it had been started a stopped without driving a good bit. After a drive it will sit at 12.8v immediately after turning the car off. And obviously read lower come morning.

    Not wanting to throw parts at this to stumble on a fix, does anyone have any clues or ideas for further investigation? I have a battery on order in Halfords which I am probably going to buy at this point, but I don't have much hope for it fixing the problem.

    Did you change it yourself, connect all cables correctly, what type car?


  • #3
    Alanstrainor
    Registered Users, Registered Users 2 Posts: 23,157 ✭✭✭✭Alanstrainor


    RandomViewer wrote: »
    Did you change it yourself, connect all cables correctly, what type car?

    Damn, title changed to include the car. 2006 Lexus IS250 V6 auto.

    Yes I replaced it myself. All tight, and connections have been checked and rechecked. I did have a suspision that the ECU plug to the alternator was not connected right, so I removed, examined and plugged it back in and made sure it was tight.


  • #4
    RandomViewer
    Registered Users, Registered Users 2 Posts: 6,191 ✭✭✭RandomViewer


    Alanstrainor wrote: »
    Damn, title changed to include the car. 2006 Lexus IS250 V6 auto.

    Yes I replaced it myself. All tight, and connections have been checked and rechecked. I did have a suspision that the ECU plug to the alternator was not connected right, so I removed, examined and plugged it back in and made sure it was tight.

    ECU might not be recognising the new unit, Lexus forums seem to bring it up as a common fault


  • #5
    Alanstrainor
    Registered Users, Registered Users 2 Posts: 23,157 ✭✭✭✭Alanstrainor


    RandomViewer wrote: »
    ECU might not be recognising the new unit, Lexus forums seem to bring it up as a common fault

    The thoughts of having to take out the damned thing again have me searching for absolutely every other avenue first! It's a pig of a job, but second time around will be easier obviously. Deep down that's where my suspicion lies...

    The ODB2 scanner shows nothing as far as codes. Not too surprised there.

    I guess I could disconnect the 4-pin connector and check the voltage on each, it's not a guarantee that it's working if I find voltage, but it would give some indication from the alternator side.


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