Battery light on dash

Does a battery light usually mean a new alternator. 289K on this one so Im ok getting one. But my truck is running like its missing bad. To the point that I think things could be so bad that the motor could be blown. I dont think I can take it back if its not it.

 

Easiest way to tell is to unplug your positive (+) cable from the battery terminal. Make sure it don't touch anything or else you'll run into more issue. If the vehicle turns off, you have a bad alternator. If the vehicle remain idling, you may have a bad battery.

 

Check the voltage at the battery with a multimeter. Should be more than 13 volts if the alternator is still functioning. Ideal is +14 volts.

If you don't have a meter, any auto parts store can check this for you.

 

Please do not unhook the battery with the engine running, it's not a very good test not to mention voltage spikes from doing so can damage electronic components. Buy a cheap meter and check battery voltage with the engine running, blower and headlights on high, you should have 13.2-14.8v.

If the truck is running that poorly I would address that before going after the alternator.

 

Never had an issue doing that for a number of years and on plenty of cars and trucks. I understand for newer vehicles that rely heavily on electrical but not for our first gen.

Yes there's plenty of ways to go about this as mention.

 

I do this when I suspect my battery or alternator is bad. My battery light turned on this summer, unplugged the red cable and truck remained running. Bought new battery, light turned off.

 

Gonna see what the shop says. Breaks my heart to bring it to a mechanic. If I do need an alternator lets see what they charge me, and if it;s an Advanced auto rebuilt or new. Like most, my wife goes crazy over the cost, and Tacoma alternators cost double what a Mustang would.

 

I put this one in Nov., 2016

$180 HIGH OUTPUT 140 AMP 1995-2004 TACOMA 3.4L 4 RUNNER ALTERNATOR

https://www.amazon.com/OUTPUT-1995-...mzn1.fos.f5122f16-c3e8-4386-bf32-63e904010ad0

Still going strong! It's only $20 more than when I bought it : $160

 

Good one for the price. I bet the mechanic charges me $350.00 for a new one. The guy will call tomorrow.

 

The light can light for any charging system problem. Physical damage loose connections

I gotta agree this is a bad practice disconnecting battery cables of running engines.

This is a holdover from the days of generators

If the system voltage drops to low the ECM shuts down to protect it`self might be very near that point causing the poor running.

Good luck

 

Do not disconnect while running. You can have it load tested for free at oriellys or autozone.

Maybe pick up a cheapie volt meter and watch you tube videos to figure it out. Its a great troubleshooting tool.

 

Agreed but some people still think is a valid test for some reason, at best it will tell you the alternator is doing something, at worst you will kill the PCM or some other electronics from the voltage spike.

 

Hey if your alternator is OEM I would suggest that you just replace the brushes on it, they are less than $20 from Toyota and the job does not take much longer than just replacing the alternator. These Denso alternators are super reliable, but like anything the brushes wear over time. While you’re in there clean up the commutator, and the brushes ship as a complete little package it’s very easy to install. I’ve done it on two of my trucks and it’s one of the easiest jobs you can do while also saving you a ton of money and keeping OEM parts on your truck.

only other thing I would check is the alternator fuse in the fuse box next to the battery, that is the sense line that drives the exciter in the alternator, if that fuse is blown your battery light will be on, but it also means the rectifier or another important part in the alternator may also be broken. You can basically buy all the parts for these alternators individually so it’s worth just replacing the problem part if you have an issue.

The junk at AutoZone doesn’t hold a candle to the OEM Denso alternators, so it’s worth a few minutes of troubleshooting to do it right.

 

I should have known....Needs new spark plugs and wires. I just replaced them a few years ago. My 24 yr truck has been going thru wires. Every other year they go bad. NGK Blues,plugs $225 Also need a new alternator $400. I also need a new ex manifold that I will do. They wanted $400 for that. I replaced it years ago and will do it again with Dorman

 

Did your mechanic diagnose the battery light as needing new plugs and wires? If so, look for a new mechanic.

 

If I had an OBDll would it tell me about the wires. Asking about a cheap one

 

An OBDII scanner won't tell you anything about the plug wires. The only way to tell they need to be replaced is if they have obvious signs of physical damage, or if you pull them and check the resistance with a multi meter.

 

Ok...My truck runs smooth again with plugs and wires. Next issue that I have is my idle went from low to stalling to high idle at 1100rpm's with the new stuff. I havnt fooled with it yet, but is there a screw adjustment for idle??

 

Not really...Check all the vacuum lines that are behind the throttle body, including the pcv line.

 

No, the idle is computer controlled by the idle air control valve. I wonder if they maybe cleaned the throttle body and didn't unhook the battery to reset the idle.