Protege5 voltage nightmare. Help!

All this started when my battery light came on my p5 randomly but went away 5 seconds after, then some burning smell was coming from the car when i got out to check what happened but saw nothing.

Later that day took the car to oreillys to do a battery test because the battery light was flickering on and of when i accelerated, test said the battery wasn't getting enough voltage and was low (11 volts) so i bought a refurbished alternator from oreillys and went home to change it.

When i get under the car i see that the stud that the positive lead from the alternator is all melted (where the burning smell came from) also the little cover on the terminal was melted all the way, and the terminal itself was welded to the stud because the damm nut came completely off and left the terminal doing its thing when i was on the highway.

So now I've changed the alternator and went to test the car all the lights get super bright and my trans (i have an auto) started doing some funny stuff, i guess it was because of the voltage so i take the car to the store again and when they do the battery test, idle voltage was fine but as soon as i went more than 2500 rpm the voltage just went up like crazy to 17-18 volts so the store guy told me to just swap it because it might be bad as it was a refurbished one, so i do that and the new one its still doing the same thing but now i can do 4000 rpm until it goes crazy.

At that point i was frustrated because the damm thing blew all my headlights and i've read that those oreillys alternators are junk, so i returned that one and went to autozone to get a brand new one and that's where i am now, and it got better because the trans didn't do the weird stuff that it was doing (i think it was trying to downshift but something happened that it was kicking like crazy when i tried to go hard on the accelerator) but the voltage is still going up at 6400 rpm, and i don't know what to do anymore I've checked most grounds took a look into the fuse box, replaced the battery, changed the little actuator on top of the starter, cleaned the battery terminals and the thing is still the same, and now im thinking the ecu got damaged or something when the nut came loose, any a help or advise?
 
Last edited:
The alternator on our car is regulated by the ECU, so it's possible that you damaged the ECU.

Check the condition of the connector #2 on the alternator. It has the control wires coming from the ECU.

Screenshot_20221031-160742_Acrobat for Samsung.jpg


That connectors terminals need to be a clean solid connection. If the connection is bad, there could be a voltage drop across it so the ECU isn't getting a proper reading of the cars voltage.

I'm not sure where the ECU gets its voltage readings, but that connector has something to with it.
 
The alternator on our car is regulated by the ECU, so it's possible that you damaged the ECU.

Check the condition of the connector #2 on the alternator. It has the control wires coming from the ECU.

View attachment 313925

That connectors terminals need to be a clean solid connection. If the connection is bad, there could be a voltage drop across it so the ECU isn't getting a proper reading of the cars voltage.

I'm not sure where the ECU gets its voltage readings, but that connector has something to with it.
yeah that’s what i’m thinking either the ecu is damaged or there is a bad connection somewhere between the voltage regulator and the ecu
 
  • Like
Reactions: pcb
Our cars are different in that the voltage regulator is actually in the ECU, so a good connection between the alternator and ECU is more important.

Check the condition of these wires specifically.
Light green with a white stripe, and white with a blue stripe.

Screenshot_20221101-042411_Acrobat for Samsung.jpg
Screenshot_20221101-042011_Acrobat for Samsung.jpg
Screenshot_20221101-042202_Acrobat for Samsung.jpg



Here's a link to the service manual and wiring diagrams,..

 
Last edited:
If it were me, I'd cut the LG/W and W/L wires coming out of the ECU, and splice in new wires directly to the alternator using crimp on spade connectors.
That would bypass the interconnected emissions and engine harnesses and go directly to the alternator.

I'm pretty sure that if your car is still acting up after that, your ECU is damaged.


Screenshot_20221101-050404_DuckDuckGo.jpg

Screenshot_20221101-053032_Acrobat for Samsung.jpg

Screenshot_20221101-044901_Acrobat for Samsung.jpg
Screenshot_20221101-045600_Acrobat for Samsung.jpg
Screenshot_20221101-045837_Acrobat for Samsung.jpg
 
Last edited:
Good idea, im gonna try it and keep updating but it’s gonna take some time because i had to take the engine out to do a rebuild, thanks pcb
 
  • Like
Reactions: pcb
Just an FYI..
There are high output alternators available for our car.
Our stock alternators are pretty weak at 77 amps.


Screenshot_20221101-065059_DuckDuckGo.jpg
Screenshot_20221101-065122_DuckDuckGo.jpg
 
Is there a benefit in running one of those? apart from all the extra amps you get.

Mostly for people who want to add a stereo, but driving in the winter with all your wipers going, your interior fan on defrost going, both engine fans going (because the AC is running), rear defrost going, your headlights on, and your stereo turned up, you max out your alternator and start pulling from the battery.

You're not supposed to operate more than two windows at a time on our car, because you can blow the 100 amp main fuse.
 
Back