# Alternator failure and mileage? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [May 11, 2025, 5:49pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220 "2025-05-11T17:49:08Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 11, 2025, 5:49pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/1 "2025-05-11T17:49:08Z")
2009 Corolla with 145k We had this car for about 2yrs. Yesterday after car wash it would not start - jump start worked. Shop tested and said “Diodes failed” on their machine. I came home and used multimeter - then it showed a voltage of 13.62 at idle and when gently revved up, it went to 13.7v. This morning: - Batt idle voltage was 12.56v - I was expecting at least 12.6v - it could be battery was drained a bit due to issues. - when engine was running, it showed 14.26v. Shop tested and said alternator passed (Reg, Diodes, Output). Did my pressure wash caused it - perhaps a short? Or Alternator is beginning to go bad? BTW: Thinking of changing the Serpetine belt: Comments on Bando, Dayco belts? ---
**Author:** ![It\_s-Me](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/it_s-me/32/12660_2.png) [@It\_s-Me](https://community.cartalk.com/u/It_s-Me)\ **Post date:** [May 11, 2025, 6:09pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/2 "2025-05-11T18:09:31Z")
> [@sciconf](#): > > Shop tested and said “Diodes failed” on their machine. > I came home and used multimeter - then it showed a voltage of 13.62 at idle and when gently revved up, it went to 13.7v. Just because it’s putting out voltage, doesn’t mean it’s putting out enough amps. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [May 11, 2025, 6:21pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/3 "2025-05-11T18:21:29Z")
Just a side note, probably not your issue, but make sure your water pump (external) pully hub is not coming off, mine blew off and never lost any coolant, it’s a very long shot but my 2009 had less miles, but probably driven much harder… The car wash could have just gotten the belt wet and it slipped some, I would just kept an eye on it… ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 11, 2025, 6:56pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/4 "2025-05-11T18:56:09Z")
> [@davesmopar](#): > > The car wash could have just gotten the belt wet and it slipped some, I would just kept an eye on it… This car usually first thing in the morning - the belt slips. For my hand is tight. Should I just change the Serpentine belt and keep an eye on Alternator - Bando cost $20 on Rock auto? ---
**Author:** ![bcohen2010](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@bcohen2010](https://community.cartalk.com/u/bcohen2010)\ **Post date:** [May 11, 2025, 7:17pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/5 "2025-05-11T19:17:51Z")
> [@sciconf](#): > > BTW: Thinking of changing the Serpetine belt: Comments on Bando, Dayco belts? Bando are garbage. Dayco and Gates are good belts. Also, check to see if your tensioner is in good condition. I don’t know about the 2009-2013 generation, but the 2003 to 2008 Corolla had issues with the stock tensioner, and Toyota released a TSB and a redesigned tensioner for those models. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 11, 2025, 7:29pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/6 "2025-05-11T19:29:33Z")
Is adjusting the tension bolt right above the Alternator fix the tension? There is only one belt (my integra had 3 or so belts) ---
**Author:** ![SteveCBT](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/stevecbt/32/3192_2.png) [@SteveCBT](https://community.cartalk.com/u/SteveCBT)\ **Post date:** [May 11, 2025, 8:13pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/7 "2025-05-11T20:13:33Z")
Not surprised by the alternator failure, my sons 2009 had the alternator go out 2 years ago. I doubt the car wash did it in. If you are in to the alternator and belt might as well change the water pump, my sons 2009 was replaced about a year ago. A bit tight to work the bolts but can be done. When we looked at the old pump the impellers were corroded and showed a lot of wear. If you take care of this car it will give you lots of good service. The alternator bolt is the tension adjuster. BTW use a lot of PB Blaster on the bolts before you start working on them ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 11, 2025, 8:27pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/8 "2025-05-11T20:27:30Z")
So I better replace : Water pump (shop) Serpentine & Alternator (might have it repaired) Change the Sparks myself. **NB:** Yesterday when the shop tested he had the the engine turned off and headlight turned on - then came up with diodes failed. What kind of test is this? ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [May 11, 2025, 8:39pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/9 "2025-05-11T20:39:06Z")
> [@bcohen2010](#): > > Bando are garbage based on what? ---
**Author:** ![TheWonderful90s](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thewonderful90s/32/29584_2.png) [@TheWonderful90s](https://community.cartalk.com/u/TheWonderful90s)\ **Post date:** [May 11, 2025, 8:41pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/10 "2025-05-11T20:41:49Z")
> [@sciconf](#): > > What kind of test is this? A battery test. Maybe the brushes are worn out on the alternator. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 11, 2025, 8:48pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/11 "2025-05-11T20:48:09Z")
> [@sciconf](#): > > Shop tested and said “Diodes failed” on their machine. What type of “shop” tested your battery and alternator? I have seen many customers directed to the dealer for a new alternator when they only needed a new battery. If the battery went dead while having the doors open for ten minutes at the car wash, the battery should be replaced. > [@sciconf](#): > > So I better replace : > Water pump (shop) > Serpentine & > Alternator (might have it repaired) For a dead battery? ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [May 11, 2025, 8:48pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/12 "2025-05-11T20:48:29Z")
> [@sciconf](#): > > What kind of test is this? I wouldn’t bring my vehicle back to that shop. Tester ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 11, 2025, 9:56pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/13 "2025-05-11T21:56:37Z")
Thanks all for the contribution. @bcohen2010 Bando is the Toyota OE manufacturer. Perfect fit. Gates a good brand that gives life time warranty. Gates spec might be little off. O’Reilly in Calif has many young non-english speaking boys working there - i know for sure that he was uncomfortable - he complained that the m/c was not responding - he put the deice on the car so I could see it - I was reading it and translating it to him so he responded for “Y” and etc. I went back (what is funny is the same guy privately told me with **confident** he did it yesterday!) and the big guy just said its all electronic and the device asks to do that - unsure if he was defensive or he is not in the mood. I did tighten the tensioner above the alternator - car has been making a squeaky sound as if the belt slips. Maybe the belt needs to be changed. If I do not have to change the water pump, I can leave it in there. But the car is moving to east cost. So I want to do all the preventive maintenance especially around here I know shops. Tips appreciated!!! Going back to the original issue, perhaps there was a short while pressure washing the car or there is an intermittent issue on the alternator. Car has seen a lot of rain in the last 2 yrs. Few other car washes but never an issue like this. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 11, 2025, 11:01pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/14 "2025-05-11T23:01:22Z")
> [@sciconf](#): > > O’Reilly in Calif has many young non-english speaking boys working there - i know for sure that he was uncomfortable - he complained that the m/c was not responding I have been to O’Reilly auto parts stores but never to an O’Reilly auto repair shop. Is the m/c the store manager or the master of ceremonies? Those handheld battery and charging system testers are unreliable, the battery and alternator should be retested properly before replacing parts. > [@sciconf](#): > > perhaps there was a short while pressure washing the car or there is an intermittent issue on the alternator. A short circuit that could discharge a battery in a few minutes would create a lot of heat and possibly a fire, it is unlikely that occurred. > [@sciconf](#): > > Few other car washes but never an issue like this. Do you pressure wash the engine during each car wash? Even if the belt slipped for 30 seconds, that would not discharge the battery, the vehicle could be driven for 20 minutes with a failed alternator or slipping belt. ---
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [May 11, 2025, 11:06pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/15 "2025-05-11T23:06:43Z")
O’reilly doesnt have repair shops, afaik ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [May 11, 2025, 11:26pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/16 "2025-05-11T23:26:12Z")
> [@sciconf](#): > > - he complained that the m/c was not responding What does m/c stand for ? And if this vehicle needs to be in decent shape before you send it across the country have a real shop give it inspection and quit guessing. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 11, 2025, 11:46pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/17 "2025-05-11T23:46:24Z")
m/c was not responding → machine was… O’Reilly was indeed the auto parts store - sorry for the misuse Battery & Alternator were retested after they had a 12hr sleep. So what did really go wrong yesterday? Alternator has intermittent issue? ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [May 11, 2025, 11:48pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/18 "2025-05-11T23:48:28Z")
> [@sciconf](#): > > m/c was not responding → machine was… You used m/c for the word machine ! How is anyone supposed to know that ? ---
**Author:** ![JoeTro](https://avatars.discourse-cdn.com/v4/letter/j/13edae/32.png) [@JoeTro](https://community.cartalk.com/u/JoeTro)\ **Post date:** [May 12, 2025, 2:39am UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/19 "2025-05-12T02:39:06Z")
Clean your battery cable ends and make sure they are tight. Also adjust your alternator belt tension and make sure it isn’t slipped (look for a “glaze” or shininess on the inside of the belt). Then see how the car peforms for a few days and re-test using a multimeter placed on the + and - of the battery (set to 12V) and make sure you get a reading around 14V or higher when you rev the engine. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [May 12, 2025, 2:59am UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/20 "2025-05-12T02:59:36Z")
> [@JoeTro](#): > > (set to 12V) and make sure you get a reading around 14V or higher when you rev the engine. How do read 14 volts or higher if meter is set at the 12 volt scale? Tester [Next page](https://community.cartalk.com/t/alternator-failure-and-mileage/200220.md?page=2)