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Ask Jared D Your Own Question
Jared D
Jared D, ASE Certified Technician
Category: Toyota
Satisfied Customers: 1591
Experience:  Shop Supervisor at County Fleet
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Electrical issues

Customer Question

electrical issues
Submitted: 1 year ago.
Category: Toyota
Expert:  Jared D replied 1 year ago.

Let me see if I can help. What kind of readings did you get when you ran your tests? They should be as follows:

1. At the alternator, the large Black wire should have battery voltage.

2. The Green/Red wire should also have battery voltage. This comes from the 7.5 ALTS Fuse.

3. Verify that the Red wire has 12 volts with the ignition switch on. This comes from the 10 amp GAUGE NO 1 Fuse.

4. If the Yellow wire is grounded, the charge light will come on.

5. The Blue(L) wire at the alternator that goes to the ECM should have 12 volts with the key on.

6. When the engine is started, the Pink (or Black in some cases) should have 12 volts and the Gray (sometimes Yellow) wire should have a square wave signal. If these are correct there should be battery voltage present on the Blue wire to shut off the charge lamp.

Customer: replied 1 year ago.
let me explain a little further. Me and my family drove 1.5 hours out of town and when we got there we parked the car overnight. No problems. In the morning we turned the car on and got the indicated lights in the picture and the car was in shift lock. Turned the key off and tried it again. Everything went back to normal. Drove back home no problems. Went to start it the next day, and same problem. Bunch of lights, entire climate control dead, power windows work intermitently, wipers don't work, flahers don't but hazards do. All interior lights do. Reverse lights don't. Radio works. Headlamps and highs work.2 days ago I checked the voltage coming from alternator and it was at 13.6 volts. Battery was at 11.98 running. Checked today and alternator seemed to not be charging. Took the car to oreilys and got a P0705 and P0500. They also scanned and they said the voltage regulator failed. I replaced the alternator. same problems and no difference. I rechecked the fuses and so far everything checks out. I checked for Ohms resistance.
Customer: replied 1 year ago.
Lost power steering, power windows, flashers, wipers, reverse lights,
Expert:  Jared D replied 1 year ago.

Electrical stuff is really hard to diag over the computer.

You checked all of the engine compartment fuses right? 10 amp GAUGE NO 1 fuse, 7.5 amp ALTS fuse? Sometimes a seemingly unrelated fuse will blow and cause all kinds of problems.

If the fuses are good it might be an intermittent ground issue. That would explain the two codes they pulled; the modules keep losing ground and triggering signal loss codes. Check your chassis grounds and your negative battery cable connection on both the battery end and the engine end.

I have also heard about 20 times that these vehicles don't respond well to re-manufactured or aftermarket alternators. I'm a big fan of re-mans because of the warranty, but apparently something in them doesn't work well with the electrical system on the Rav4. Would it be feasible to put an original toyota alternator on it? I know it's at least twice the cost, but that might be what it takes to get it going again.

Customer: replied 1 year ago.
Whats interesting is the alternator change didn't affect anything after the install. Same lights same voltage. Would a "dying" battery cause the ECM to regulate what available power goes where?Yes I checked every single fuse visually and with a multimeter.Are the modules connected at ground or up the chain? My thoughts are, what would throw the codes, and at the same time disable climate control, flashers, wipers and reverse lights and power windows? The codes may be correct but would those codes cause any downstream power failures?
Expert:  Jared D replied 1 year ago.

No, the ECM on this model isn't "smart" enough to ration available voltage to each system because of a dying battery. However, on the subject of a dying battery, one with a bad cell could test fine with some battery testers but cause the voltage to the PCM to be irregular. The battery acts as a kind of second stage voltage regulator on Toyotas. If the battery has an internal short it could prevent the alternator voltage from reaching the PCM correctly. Which could cause all of the problems you are having.

There should be a ground at the fuse/relay box, and one on the PCM, in addition to the chassis ground from the negative battery cable.

No, I don't think those codes would indicate any electrical related problems in general. The p0705 indicates a voltage problem in the transmission neutral switch. The p0500 is an irregular voltage pattern from a speed sensor.

Customer: replied 1 year ago.
Is there any other governing force that would cause the alternator to not charge around 13.5 volts? I am just baffled. I ran an open circuit from battery neg to alternator housing. Got an open circuit. Red alternator to Battery neg was continually 12.05v.
Expert:  Jared D replied 1 year ago.

Not the way you are testing it. If you are running a jumper from the neg to the alternator housing and you know you have good batt voltage to the alternator on the pos side it should put out full charge. You are essentially bypassing the rest of the electrical system and eliminating any other module as a possible fault.

What if you pull the alternator and have it tested on a bench at the parts store? Does it test good or does it show diode ripple? What about the battery? Have you had it load tested with a good carbon pile type tester?

Customer: replied 1 year ago.
bench tested alt and batt at oreilys. I am not sure what kind of tester they have. However when I installed the alt back in, i had them retest and they said the voltage regulator failed. Thats when I bought a remanufactured alt and installed. Symptoms are the same.To test voltage from alt, how do I test it with a multimeter?
Expert:  Jared D replied 1 year ago.

You should see around 14.9 volts at the battery terminals, or at the positive terminal on the alternator within a few seconds of starting on the multimeter. You should also see around 14 volts from the black wire which comes from the ECM B30 pin 50.

Expert:  Jared D replied 1 year ago.

I know it's not the best option, but I think you need a new battery and another new alternator (preferably an original toyota). I just don't think yours is working correctly.

Customer: replied 1 year ago.
the low voltage would cause the PCM to wig out and possibly throw a bunch of codes?
Expert:  Jared D replied 1 year ago.

Yeah, definitely.

Customer: replied 1 year ago.
quick question... I think i over looked something. when testing the fuses under the hood with a check light, only some of the fuses glowed red when the light is connected to the hot battery teminal. Others would not glow. I would have to switch to the negative post and retouch those fuses that didn't glow first, and then they would make the light glow. Is that indicative of fuses that only work when motor is off, or should all of them be passing all the time?
Expert:  Jared D replied 1 year ago.

Some fuses are powered, some grounded, which means if it is a grounded fuse it should light a test light when the opposite end is on the positive terminal, and vice versa for a powered fuse. They important factor is whether both sides of the fuse are the same. The best way to test them is with a multi-meter. Check resistance across the two sides of the fuse.

Customer: replied 1 year ago.
Got it. Was the starter relay inside the kicker panel.
Expert:  Jared D replied 1 year ago.

The starter relay was casing the the alternator to not charge? That's a new one for me.

I'm glad you got it going!

Customer: replied 1 year ago.
Yeah the starter relay when working properly tells the alternator to charge the battery. If the starter relay is bad, the computer doesn't know that the car is even running. No ac, wiper, power windows etc...
Expert:  Jared D replied 1 year ago.

So it will still run the starter but not complete the circuit for the alternator? I'm going to write that one down.

Customer: replied 1 year ago.
Apparently. Who knew. Swapped the relay with low beams, voila.
Expert:  Jared D replied 1 year ago.

That's awesome! I'm sorry I couldn't be more helpful. Electrical stuff is tough to diag in person, not to mention over the computer.

Expert:  Jared D replied 1 year ago.

I just wanted to check in and see if you needed any additional information on this question. I haven't yet seen a rating from you and was hoping to have helped in at least some way in diagnosing this problem.