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Old 07-30-08, 04:46 AM   #1
aleksg
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Default RX 300 fuse box

Hi guys thanks for all advice and help but i still got copule of more questions if thats ok .

When my RX 300 (year 2000) arrived my alternator fuse 120 Amps was completely melted down. Some other fuses were blown too but not melted this one was completely done. Anyhow we put 100 Amp fuse because i figured its not much of a difference to see how is it gonna last. Anyhow i still havent driven my rx cause i have a jerking problem when i step on the gas and this electrical problem. Anyhow ill get back to the fuel pump later. So every morning id start the car for about 15 mins just to keep the battery happy But 2 days ago i found that the alternator fuse has melted again. So i took it to an electrician who tested the alternator and the regulator and claims that its working fine and that he cannot find the reason why the fuse is melting. So we put some copper wires for a test and found out that they get extremly hot before they cool down. So his solution is to put a much thicker copper wire and let it stay as he cant see any harm in it. Now to me that sounds dodgy because manual says that fuse is supposed to be 120 Amps and not more. Any advice guys or thoughts?

Thanks
Aleks
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Old 07-30-08, 06:05 AM   #2
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You have a very serious electrical problem if you are experiencing multiple fuse "meltdowns". Bridging the fuse with a copper wire is extremely dangerous, risking a whole laundry list of expensive electrical components in your RX.

If your "electrician" thinks bridging fuses to see what else pops is a good idea, take your car somewhere else before he destroys it. DC electrics are complex and frustrating to service for most of us, take your baby to a QUALIFIED mechanic who is familiar with sophisticated automotive electronics.
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Old 07-30-08, 06:27 AM   #3
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not a multiple fuse meltdown its a alternator fuse that melted down. unfortunately this guy is as qualified as it gets where I live in which is Zimbabwe and the government here managed to bring everything here to its knees which means 90 % of the QUALIFIED mechanic shops closed down. This guy was refered to me by toyota zimbabwe as there is no lexus representative here. All im trying to do is get my car running so i can drive it to South Africa and leave my car in capable hands of proper lexus mechanics.So until then i have to get it running this is why if u have any adivce on what could be causing this Alt fuse to heat up id very much appreciate . thx!

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Old 07-30-08, 06:42 AM   #4
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Could be a short some where in the wiring,but what this guy is doing could cost you a wiring harness at the very least.I`m hoping that Lexmex,or one of the others (w/more experience in electrical problems) can add some advice for you.Electrical issue`s can sometimes be a nightmare for an unqualified individual.
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Old 07-30-08, 09:00 AM   #5
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There are two ways to do this.

1. Smoking gun: You bypass the fuse with heavy copper wire and the circuit which is drawing the large current smokes out (the point of large draw burn up or a fuse down the line pops). This is dangerous but quick trouble shooting process. You run the risk of fire at the point of current draw, wires melting insulation, snap connectors corroding up.

2. Isolation: Highly recommended ... You remove as many loads as possible )either by disconnects or removing fuses) and you monitor current. The offending circuit when brought on line will cause the large current draw. Then it is a matter of tracing that circuit.


The above are the logical ways to hunt down a problem. Sometimes a thorough visual and smell test can lead you to a problem too.

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Old 07-30-08, 10:00 AM   #6
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the first option is what i think my elctrician tried but xcept for the wire itself heating up and then after a little later cooling down we couldnt find where the problem is coming from as that fuse is for the alternator only according to the manual
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Old 07-30-08, 03:41 PM   #7
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I want to take a look at the alternator fuses tomorrow morning.

I was wondering if you could describe the jerkiness you are getting when you step on the gas.
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Old 07-30-08, 04:24 PM   #8
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Well when you are pulling off and step on the gas the car just starts stalling or jerking, so you have to press real slow and then it starts getting power. I had toyota do diagnostics of the vehicle (thats basically ALL they could do as they have no spares or knowledge). This is the report i was given:

- Misfiring - suspecting spark plugs.
"These i had a look at and the electrcian claims that they are fine as the ones you get here are of poor quality so we cleaned em out and placed them back."

- Jerking and Hesitating - Suspecting fuel restriction from fuel pump or filter.
"Now me and my mechanic after about 5 days of looking for this fuel filter finally removed the back seats and took the pump out. We thought maybe because this car sat without moving for over 6 months the tank would be dirty and the fuel filter would get dirty too but to our surprise the tank was crystal clear, also this car has only around 65 000 kms and i read on the forums here that the filter does not change untill over 12 000. I am now waiting for a gauge to test the fuel pressure."

- Battery light not coming on and the vehicle is not charging.
"Basically my previous electrician who looked at this took the alternator out and we managed to find a similar regulator that we fitted in. checked the voltage was at around 13.9 which meant it was charging now. We could not find a 120 Amp fuse so we put 100 Amps.Now that also melted down and i went to this electrician who is working on all the latest modern cars here but he cannot identify the problem. He claims that the fuse is not shorting but heating up and melting so he suggests just to double the fuse by making a thick copper wire and bridging."

Thats from Toyotas diagnostics
I have ordered 3 x 120 amp fuses, fuel pump, fuel filter and alternator regulator and they should be arriving any time soon.
I fear that even 120 amp fuse wont be enough though because when you touch the copper wire which is way more than 120 amps it gets really really hot. However, the electrician monitored the car running and after some time the copper wire starts cooling off.My electrician guarantees that this is only the fuse for the alternator and that it should be no problem to just bridge it.Also when the car arrived the speedometer was not working and is still not working. Anyhow these are my problems with my RX

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Old 07-30-08, 06:14 PM   #9
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If you mean by diagnostics, I assume they plugged a scanner into your vehicle and got some codes. If you have those codes, I could help tell you what the issue is. Misfires are usually P03XX codes. In a very worst situation since you wouldn't have access to extra ignition coils (as opposed to spark plugs which fit inside the end of the ignition coil), you could disconnect the fuel injector and run on fewer cylinders. Those issues can occur due to the quality of the gas (something I know all too well after frying a coil and some catalytic converters in Mexico). There are some Toyota ignition coils that might be able to be modified for your vehicle. The Camry is one such possibility (it was in my case). About the only thing that I see out there that could be a possibility would be an Avensis, I am not positive about a Corolla ignition coil.

I considered removing my fuel pump and changing out the filter down in Mexico, but running U.S. gas now it runs a lot better. Still, I have had some air/fuel sensor pending codes a few times back in Mexico because I let my vehicle sit for between 1 and 2 weeks such as when I went home for Christmas vacation. I have actually had this happen to me once in Florida when I let it sit for a week without driving it when I had to do some travel. In Mexico, I used fuel additives to help clean up most of the issue. I don't discount you could have an issue, but I haven't seen anyone had an issue on this board with the pump or filter itself. The jerking and hesitating I think could be an ignition coil.

Yes, 65K kilometers is a young vehicle.

I will defer to what your mechanic and Salim have mentioned. I don't have firsthand experience with my RX300 and that electrical issue. It's actually the first time I have seen something like that occur with this vehicle.
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Old 07-30-08, 06:19 PM   #10
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Some thoughts:

- I'd look for signs that an animal has been chewing on some part of the wiring harness.

- I'd consider towing the car down to South Africa. The risk in driving the car with the fuse bypassed is probably greater than the expense of towing. This could include major damage to the wiring harnesses, engine fire, or who-knows-what.
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Old 07-31-08, 03:40 AM   #11
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They gave me no codes whatsoever just a paper with the writing that i typed here . Like i said i can order parts from overseas if its the ignition coils then i will have to order them but strangely my electrician did not say that there was anything wrong with them, well he didnt mention them. How would you know if the ignition coils are the problem? I suppose if the pump is tested and the fuel pressure is good then it had to be the ignition coils?
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Old 07-31-08, 06:29 AM   #12
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Quote:
Originally Posted by aleksg View Post
They gave me no codes whatsoever just a paper with the writing that i typed here . Like i said i can order parts from overseas if its the ignition coils then i will have to order them but strangely my electrician did not say that there was anything wrong with them, well he didnt mention them. How would you know if the ignition coils are the problem? I suppose if the pump is tested and the fuel pressure is good then it had to be the ignition coils?
There is a little test where you can take out, one by one, the ignition coil with the spark plug still attached to the bottom, disconnect the fuel injector and start up the vehicle and see if there is a spark. I usually have done it without disconnecting the fuel injector because it takes just a few seconds or so.

Ignition coil should look like it is in this position when you start the test (leave all the other coils in place), but where the white arrow is, that is where the spark plug should be placed. You have to do this for each ignition coil, one at a time, leaving the other coils in.

For those of you with the service manual, this procedure is outlined in the Ignition section (IG-1).
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Old 07-31-08, 06:57 AM   #13
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Here is the thing for checking the codes.

You have to look here (should be roughly same location if you have a right hand drive vehicle only it will be above your right knee), but on left hand drive the OBD2 port is right here.
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Old 07-31-08, 06:58 AM   #14
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However, in order to read the codes you need something called an OBD2 scanner. I am not sure if anyone there has one. They come in all shapes and sizes, but this is the one that I use.
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Old 07-31-08, 07:17 AM   #15
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I took a look at the fusebox just now to confirm (would like someone else in our forum to confirm this as well).

There are two alternator fuses.

One fuse, Alt-H is the one in the white box. It says 140A on it.

A second fuse, Alt-S is the one in the yellow box. It is 7.5 A.

Now what I can't be sure of is that other models in the world use different amps on that particular fuse. However, some online searches show that at least in this part of the world, 140A is what is standard on these vehicles.
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