Failing alternator?

Jimmy Brooks

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Was up in Santa Clarita with my buddy that owns a 4Runner TRD Pro doing a little night time off roading. We were out there for around 5 hours and since it was night I had my high beams, fog lights (you can make it so you can turn both on at the same time via IID tool) and my big light bar all on. When I finished the trail and got to a fire road I noticed that my voltage was hanging around 11.7-12V. I immediately turned my high beams and light bar off but it didn’t change much, still was hanging around 12 and my batterys estimated state of charge was hanging along 75% and dropping a percent every 5 minutes. Yet no battery light poped on the dash and when I turned off the car and turned on accessory mode the battery voltage was the exact same as it was with the car running. Me realizing that my alternator may have completely failed and I may only have so much time till my battery dies and leaves me stranded, I picked up the pace and was able to get the voltage up to 12.5 on the drive to my friends house around, 15-20 miles of driving. When I got to my friends house and turned the car off and turned it on again 5 minutes later the car was reading 13-13.2 volts and when I tuned it on the next morning it was reading 13.5-13.7 (normal) and stayed the same on a 30 mile drive back to my house and the battery charged to around 95%. So now I’m confused as to why it seems to be just fine now? I smacked my skid plate pretty hard against a rock on the trail, could it have freaked out my electrical system? Also I do have a 400w sub in the back, am I asking for too much power from the alternator and should I consider a dual battery set up? Let me know what your guys thoughts are on this.
 
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djkaosone

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Don't feel bad, I'm on the same boat dealing with power issues for YEARS. I'm on my 3rd alternator and 4th battery. I haven't had time to check it out, but a few members on here pointed something out to me and will soon dig into that rabbit hole a bit deeper.

Long story short, there are 3 PWM connectors that regulate the amount of voltage an amperage to the battery. The BMS connector at the negative terminal helps control the charging profile, main culprit and could be unplugged (with warning lights) to provide 13.8V). The "random" wire on the positive terminal that runs along the battery breathing tube has a couple of inline fuses, the ohm reading between the ring spade and the other side of the inline fuses have to be ultra low with zero resistance. Then there's the single PWM connector on the alternator that controls the PWM signal to the ECM, and this is the wire I need to unplug, ohm test that wire with C2273H, C2274L, and/or C0570L-175. If the ohm reading shows too much resistance, I may need to run some new wire(s).

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Jimmy Brooks

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Don't feel bad, I'm on the same boat dealing with power issues for YEARS. I'm on my 3rd alternator and 4th battery. I haven't had time to check it out, but a few members on here pointed something out to me and will soon dig into that rabbit hole a bit deeper.

Long story short, there are 3 PWM connectors that regulate the amount of voltage an amperage to the battery. The BMS connector at the negative terminal helps control the charging profile, main culprit and could be unplugged (with warning lights) to provide 13.8V). The "random" wire on the positive terminal that runs along the battery breathing tube has a couple of inline fuses, the ohm reading between the ring spade and the other side of the inline fuses have to be ultra low with zero resistance. Then there's the single PWM connector on the alternator that controls the PWM signal to the ECM, and this is the wire I need to unplug, ohm test that wire with C2273H, C2274L, and/or C0570L-175. If the ohm reading shows too much resistance, I may need to run some new wire(s).

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Yup, I’m on my 4th battery myself since 2010 but have never replaced an alternator before. To my surprise tho when I was experiencing this low voltage everything was functioning properly and non of the lights were dim nor did I get any faults or warning lights. So my question is should I be worried? If I had been in this situation but for another 2 hours with all lights running would my battery have eventually died and would I have been stranded? Should I look into replacing something. Everything is still working fine and volts are normal now but it just makes me nervous that the alternator seemed to not be working when I needed it most.
 

ryanjl

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If it helps calm your nerves, the alternator on these are Denso units, which is the same one that Toyota runs. They regularly go 200k plus miles. The main issue with the LR4 is the location of the alternator. It can get mud in it or even oil from the engine. Barring that, it should last a long time.
 

ktm525

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My alternator failed at 120k miles. New Denso back in. When mine failed it had a loud whine. When I replaced it it was very very hot. I plan to rebuild it.

My Honda Ridgeline (Denso) alternator also failed at almost the same mileage and age (11 years).
 
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t3s1a

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Normally, alternators live 100-150k mi or 10-15 years. If you reach those numbers it is a good idea to replace it with the new unit and service the old one to keep it as a spare part.
LR has a smart charging function that regulates charging depending on conditions, so it won't give you a constant 14.5V as other cars do while running. As long as the battery has 12.5-12.7V (fully charged) on its terminals in the morning before you start it, you have nothing to worry about.

Measure the voltage on battery terminals directly!
 

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