My 2008 Tundra Grade 5.7L 4x4 has an unusual alternator problem with 148000 miles on it. When I turn ignition on the battery light will come on and upon start it goes out as normal. I noticed the voltage gauge being between 9 and half way mark which means it was not charging. Voltmeter check confirmed it was not charging. I have researched and checked all associated fuses to be good. I have not checked right at alternator yet as it will be a pain to get to. Has anyone else found the alternator to be bad with the light acting normal? Before I go further I would like to have an alternator to replace on hand if others have had this kind of problem and replaced the alternator and not just bad connections at alternator. From what I read the average alternator lasts only 7-8 years and up to 150000 miles. I have had many cars go over 200k with no alternator problems and wonder if this is just a Tundra problem. Seems to me that charging cable from alternator to the fuse would have a bad joint at alternator since the alternator is telling the light not to come on as alternator is saying everything is fine. I know strange things can happen for it to be a failed alternator and just checking to see what others have found. Also thinking to be preventive and replacing anyway if this is a common problem with Tundra...Thanks
alextv71
With it running does the volt gauge drop or go higher when you turn on the headlights? Take the truck to an auto parts store and have a load test done on the battery before you start stockpiling "what if" parts. An alternator needs to be "excited" on start-up. Most of the time just driving them gets the job done. When I converted my Model A to an alternator, I always had to give it a little rev of the engine to get it to swing charging.
Welcome to the forum, and remember to ALWAYS "enjoy the adventure"... Chap
Welcome to the forum, and remember to ALWAYS "enjoy the adventure"... Chap
Any load drops the voltage. The light goes out upon start which makes me think it could be a bad connection at alternator. The light is triggered by alternator output voltage being less than battery so the monitoring system is thinking alternator is working. I just need to check at alternator to confirm what the problem is which is a pain to get to. I have seen a lot of strange things happen with electronics and that is why I posted here to see if others here have had the light go out and be a bad alternator. Thanks
I think Chap's right though. Do the physical searching around you are for obvious signs of something wrong, but I've seen a lot of threads on here where a bad battery created all kinds of weird problems the owner never thought it would have.
A load test is quick and cheap, sometimes free depending on the shop.
A load test is quick and cheap, sometimes free depending on the shop.
I am out of town and won't be able to completely diagnose for couple more weeks. As I had stated before I had checked all associated fuses hoping that was the simple fix. My next step is to measure all the voltages at alternator and if everything ok there to proceed with replacement. I will post back here when finished so others will know. If I had not had the voltmeter on the truck I would have been stranded because the idiot light was acting normal. Thanks for your input.
If you have a scan tool (WELL worth the money to buy... if it saves you a misdiagnosis it could pay for itself right there..), it might have a subroutine for alternator testing. Worth a try if you have one. Probably your alternator is just going bad. My 2003 escape ran on the original till it hit 212K miles, then it failed. Died while driving, jumping starts right up, dies again in minutes. When I replaced it it wasn't charging at all. Popped in a brand new unit, no problems.
Probably yours is just going bad. 148K for a $200 part isn't a big deal at all IMO.
Probably yours is just going bad. 148K for a $200 part isn't a big deal at all IMO.
After checking all voltages at the alternator I diagnosed the problem being the alternator. A new alternator fixed the problem. Still strange that the monitoring IC regulator system within the alternator assumed all was well by not turning on the light. If it had not been for the dash voltmeter I would have been stranded. A voltmeter is all that is needed to diagnose an alternator problem. It was a gigantic pain to replace.
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