Hello,

I was hoping someone could shed some light on the problem that I have here. The battery light came on about a week ago and a few days later it just died. I figure that replacing the battery would solve the problem but after a battery swap I had the same problem. I pulled the alternator and had it bench tested at 2 places. Both tests had the following results:

Battery Volts: Low: 13.50. Actual: 14.73. High: 15.40
Ripple Volts: Low: 0.00. Actual: .51. High: 2.00
Lamp Volts: Low: 0,00. Actual: 2.62. High: 8.00
Lamp Off Volts: Low: 13.00 Actual: 14.3 High: 0.00


I can jump can jump start it and it will last about a mile but then dies. I don’t believe the battery is being charged but then the alternator will not keep the truck running.

I guess the wiring has to be checked and I am not the best at electrical and need a place to start. I have had for about a year now an engine light on with misfire on Cylinder 2.
VSG lights on come on with engine light. Anyone have any ideas ?

 

Update: So I put a volt meter on what I believe to be the output of the alternator and I could steadily see the voltage drop when I pulled the cables off….. Based on the bench test then it would have to be something leading up to the alternator ? There is a plug going into the alternator which I assume would be the ground and maybe a switch that turns the alternator on and off with the key ? This is way out of my area of expertise …..

 

So the fuse (7.5a) going into alternator through the wire harness is good

I feel like the next step would be to swap the alternator but the bench test would suggest otherwise

 

Ok, Here's the schematic of the alternator. If you look at it, the alt's main output is the connector marked B. That's where the alternator's output to the battery, and thence the rest of the truck's systems is. It's a bolt on the side of the alternator, with a thick, white wire, actually a fusible link, on it. It's usually covered with a red rubber cap.
Generally, after starting the truck, it will be about 14.5 VDC to charge the battery back up, and run the truck as well.

The other wires that go to the alternator are in the small plug on it. IIRC, the one marked S is the alternators field coil supply. The one marked L is the sensor wire that allows the CHARGE light to come on if the voltage on it drops below a certain level. The one marked IG is the one that senses the battery voltage, to control the output of the alternator. I believe. I may be wrong on the 3 small wire in the plug, but I believe that's what they all do.

The main one to check is the B wire. If it's not good, then check the other wires. Notice they are all fused, so the fuses are the first thing to check. If the output of the B terminal is good, but the battery voltage isn't, chances are one of the fusible links, the thick, white wires, may well have burnt open. They are designed to allow the wire inside them to burn without damaging anything the wire goes near. You may not see any external indication at all. Only way to tell is by ohming them out. Remember to remove both battery terminals before ohming anything, as even a small voltage on the wire you're checking can damage your meter.

Does all my rambling help any?
Pat☺

 

Thanks Pat ! Yes that confirmed a lot of what I was doing to test it. So now when I measure the voltage coming out of the Alt after getting it started with a jump it says like 6V. So now my dilemma is that they bench says the complete opposite ….. I read that it also could be a bad ground where the alt and the bracket that holds it in meet but this appears nightly improbable. I think that all I can do now is try and swap it out. Know anyone in Sd with an Alt laying around ?

 

^highly

 

So I hope that this helps someone.

I swapped out the alternator for a used one that I got off eBay. ($50.00 & came out of a Tundra). I’m not sure this is a permanent fix but just before I installed I bench tested it and it passed and it’s voltage output is over 14v.

Here is the strange part then which I’m sure you have already done the math if you read the entire post.

I had the original alt tested 2x on the bench and both times it passed but when in the vehicle it only would output like 6v. So for whatever reason the alternator was fine on bench but failed in Truck..

I don’t know and have no explanation. It looks to be an aftermarket alt ….. not Toyota / maybe I’ll look a little closer later.

 

This may be part, if not all, of your trouble. Toyotas quite often don't get along with after market parts very well. They may appear to be perfectly good in all tests, until they are installed, then they fail in unique ways.

If possible, get a remanned OEM alternator to put in. Verify all the wires going to the alternator are good. Remember, the alternator needs at LEAST 12 volts from the battery to provide the proper output voltage. It's the excitation voltage. Without the proper battery voltage TO the alternator, it can't produce the correct voltage output TO the battery to keep it charged.
Could you have a bad connection somewhere in the excitation voltage wire to the alternator? Or one of the fuses, or fusible links. Some dirt, corrosion, whatever, in the wire's run is all it takes. That would cause the low output voltage.

Might be worth a look, anyway. Good luck!
Pat☺