8E0S8

Hey guys so my problem is same as the title. I have done research and tried to fix this on my own as I don't really trust anyone else with my car and I don't like paying for overpriced repair. ill try to put as much detail as possible, to rule out any obvious possibilities you may have.

So one day my car started feeling weak. Slow accelerations and wouldn't even roll forward when brakes were let go. I thought it was just because I was on a hill. I made a stop to do an errand, then when I tried restarting my car, it turned on then died. I tried to start it again and was able to get home. Two things to know is:
1)I replaced my battery maybe 5 months ago
2) when I was parking to do my errand, the car would jerk when I put it in reverse. As if I was pressing the gas while changing gears. It was pretty rough and I thought my trans was broken. CEL also came on. When I got home it didn't happen again and hasn't happened since. CEL also disappeared. I don't know if its related, just noting it down

I did troubleshooting with a volt meter. Battery would be a healthy voltage when car was off. Turning it on would raise voltage to a little over 14. When I turned on all lights and radio voltage would drop slightly, maybe 13.8. 13.6 at the lowest. Some might say that's not ideal, but it remained constant here. When I turned on the AC, the voltage would drop even lower, and the reading would continuously drop by 0.01 volts right before my eyes. Eventually it would get to the 12s, which isn't good at all for a running car. My conclusion was that it was the alternator.

Bought an alternator from napa[rebuilt(not my choice)]. I know that rebuilts aren't as good as OEM and read that they don't replace everything. Just fix it up to spec. I replaced the alternator, and I think it wasn't as good as OEM. it would only get the voltage to about 13.9. But hey, thats fine with me as long as the problem was solved but it wasn't. Same thing happened with the lights, voltage dropped, but remained constant after. AC would drain voltage slowly. Oh, and yes I would rev my engine while doing these tests. After feeling like I failed I gave up for the day. My conclusion now changed towards it being a problem with the AC, not mainly the alternator.

Today, I decided to inspect any wirings I could. I noticed two things,
1) plastic in the wiring harness to alternator was cracking, but the connection was still solid.
2)a ground by the firewall was on a screw but not bolted down for some reason. I couldn't follow where it connected to though.
After bolting the ground down, I fired up the car. Voltage actually got over 14. With the lights on it stayed at 13.9-14. I thought my problem was fixed! I turned on the AC and it went to about 13.7, and stayed constant for a short while then started dropping again. Now and before, revving the engine would get the voltage up a little, then it would drop back down. Rev it again, and it wouldn't go up as high, then drop down. So it's peak would get lower and lower.

other things that may help:
-AC fuse in engine bay well, there was no fuse. which is weird because my AC was still working. I replaced it and it didn't change anything, if anything it made it worse, but that could be because the battery/alternator was already low from testing.
-After today, CEL came on again, which is weird considering all I did was tighten a ground. I'll see if I can get a friend to read the code

At this point, I'm lost:
The obvious would be to:
1)put the old alternator back in and see if its better(which is annoying because it was for nothing I changed it)
2)get a replacement alternator for the replacement because I have warrenty (still annoying because my labor for their defective part)
3)try change out the battery to see if it makes a difference(I doubt it but it could be possible)

What do you guys think? Any ideas or solutions come to mind? I just wanna know your opinion before I do the annoying obvious', or go to a shop or Lexus.

Thanks guy, I appreciate any input, and sorry its a pretty long story.

PFB

Mine basically does the same thing, but no problems at all.

Find out what the CEL code is, it my be totally unrelated. Also keep in mind that when the AC is on, the two cooling fans come on to. they consume quite a bit of power, hence your voltage drop when the AC is on.

Of course it's possible that one of those fans is defective, or even stuck. If that's the case it may consume excessive power.

However, as I said, first determine what the CEL code is. If its unrelated, and your AC fans are OK, than there may be nothing wrong with your charging system.

Phil

speedkar9

As for the loss in power, start with the easy things first, like cleaning the throttle body, making sure the intake hoses are clean and not cracked, and the air filter is clean and unrestricted.

Then I'd take the car to a parts store to read the code. Then pull the battery (doing this might clear the code) and have them load test it. Most part stores test batteries for free.

Next I'd clean all terminals - two battery lugs, the starter and alternator connections. Sand them down and make sure they're making good clean contact and there's no corrosion or looseness.

How are you testing the alternator voltage? You should be testing it from the alternator wire to ground (battery negative) as opposed to right across the battery terminals.

While the multi-meter is hooked up and the voltage has dropped to 12V, you can carefully start disconnecting non-vital electrical components to see if the voltage rises back to 14V again, such as the headlights, HVAC & stereo fuses, radiator fans, oxygen sensors, etc. If you disconnect something and the voltage goes back to normal you'd have found the culprit.

What year is your ES and how many miles?

pauloil

I think you should START with a voltage drop test of your terminals and cables: the starter cables. clean the grounds and read on this chat room how to do a voltage drop test of the negative side. What shape are the FANS in: they may be drawing too much voltage as they are wearing out.

mitmaks

Why did you replace alternator and you don't even know if it was the culprit. Most auto parts stores will check your alternator/charging system for FREE.
You should check which code you're getting before you go screwing around with alternator, etc and just throw away money on random parts.

8E0S8

I had my car checked by a friend of a friend who is a mechanic. I tried to show him how the voltage drop and of course it made me look dumb and it wouldn't keep draining like before. It would drop with the AC on but stay around 13.4 which he said that is okay. Is that true? I thought it had to be around 14v + or - a little.

Anyways, he scanned my car too and the codes were P1135 and P1155 which I learned is the air/fuel sensors 1 on bank 1 and 2. Gonna check those out before I actually change them. I also took my car for a drive and I noticed it has been shifting high, like around 3k RPM even when I'm accelerating slowly. Is that a symptom of the air/fuel ration sensors being defective?

JetsonES

I had a similar problem and resolved it by replacing the ground cable coming off of the battery and going to the chassis. I used 0 gauge wire because I had it lying around but 4 gauge should work fine. You will need about 1.5 feet of 4 gauge, a new negative battery terminal and a lug or terminal for the chassis side. Remove the old wire from the chassis, sand the metal to get good contact with the new terminal and your problem should improve. The stock ground wire is either 12 or 16 gauge and is insufficient, and only gets worse over time due to corrosion.

I do this to pretty much every car I own, it's cheap insurance in my mind.