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I have run into an issue with my 2003 LS that is baffling to me. I started having issues back in March with the battery and warning lights coming on while driving. I ended up having to replace the Battery, Battery fuse, Alternator fuse (replaced with a 120A instead of 140A), and electronic throttle control fuse. After all of this was done the car ran fine with no issues up until yesterday. My wife texted me on her way to work that battery light came on, as well as a few other warning lights along with a dinging sound. She works about 2 miles from home so when I got there I had her cut the car off, and back on. At this point the car would start, but no dash lights at all and could not put the car in gear. This was similar to the issue I had originally back in March with the fuses.
I had already planned at this point to look at the car on my way home to pick her up. I had her try starting the car one more time before I got there and everything seemed normal again. She got the car home, and I picked up a new alternator fuse from Lexus on my way. Well I get home and start taking the Fuse box apart to get the old fuse out and I smell a burnt plastic smell. Come to find out the Alternator fuse was not even blown, but had literally melted. I was able to get the fuse out, but looked like there was still some hardened residue left over from the fuse. I went ahead and cleaned it out the best I could using some contact cleaner, and put the new fuse in. Bolted everything back together and tried starting the car. Everything seemed normal again for a few minutes except the door ajar light was on, but no door was open from what I can see. Then all of a sudden I smell the burning electrical smell again, and smoke started coming from the fuse box. I immediately turned the car off, and disconnected the battery.
At this point I am not sure what I want to do. Most mechanical stuff I am pretty good with, but not electrical. I have checked to see if there are any loose wires anywhere near the panel, alternator, etc but I do not see anything. Anybody have any other ideas? I can get a replacement panel, but I think I saw another thread where a guy bought a new box panel, and still had the same issue of the fuses burning. Should I have the dealership diagnose the issue and see if it is something simple? I am open to all suggestions.
The short answer to the cause of your burnt fuse is - poor connection.
Here comes the long answer… The electrical path for this circuit is designed for 140A. In an electrical system, you have a number of “loads” which will consume power and you have wires and connectors that will deliver the power to these loads. The delivery system must be designed to have very low electrical resistance.
Supposed if the bolted connection was not made perfectly and you introduced a small 0.1-ohms resistance at the interface, and let’s assume the alternator recharges the battery at 80A. According to Joule’s law, P=I²R, where, P = Power in Watts, I = Current in Amperes, R = Resistance in Ohms. So, P = (80A)² x 0.1-ohms = 640W, which is more than enough to melt plastic. This 0.1-ohms resistance is essential a "load" that acts as a 640W heater.
Since the overall current has not exceeded the 120A fuse rating and the heat is generated at the connecting point, the fuse element does not melt, and the electrical path continues to power the "heater" to heat the plastic and eventually smolder and smoke.
I replaced the burned 120A with a 140A last night. Everything came back on, but within 2 minutes smoke started coming out of the fuse box like it was heating up again.
*Prior to the tow to Toyota had to start the car to back it out of the garage. Left it running for 5 minutes and no smell or noticeable smoke from the fuse box anymore.
Had it towed to Toyota this morning since they have a free 1 hour diagnostics time. Got a call saying they have no clue what it is yet, but they are saying the battery is bad. They said it could also be the alternator going out, but they have no way to test further until the battery is replaced. Is it possible the battery I have is bad after 6 months of use? bad terminals? He also said that the car will start, but once again the dash lights are all out, and the car is unable to be put in to gear.
Sounds like your battery has a electrically shorted cell. When a cell is shorted out, there goes a big current from the alternator to the battery only when the engine is running. The voltage regulator inside of the alternator tries to regulate the voltage targeting the voltage around 14.4V@ambient although the battery's voltage is about 2V lower than normal and is only about 10V+some.
When a cell is shorted, voltage 14.4V is applied to the battery of 10V+some. The difference of the voltage is around 4V or so and there goes a big current like 100A or more. It is saturated by the limit of the alternator's capability and the fuse is not blown. A good battery's ESR is usually between 0.02Ω to 0.05Ω. Suppose it's 0.04Ω, there goes 133A (ie: 4V/0.04Ω≒100A). Strictly say, there is some internal impedance of the alternator but just disregard it to simplify the calculation.
I experience this type of failures time to time at local shops and dealers. Those mechanics working there are mostly not good at electric/electronics related affairs and I often am called a maestro by them. But I'm not good at mechanical affairs and they help me time to time.
Thanks for all of the replies. I was able to swap the battery out for free since it was only 6 months old. Car is able to start, but within 2 minutes the new alternator fuse starts to smoke again. My dad was able to come over and help me do some testing, and the alternator seems to be good. One other test he did was disconnect the fuse box itself and then run the tests. He says that the current draw is def coming from that fuse box. I have ordered a replacement box on ebay, and hope to get that replaced this weekend to see if this once and for all solves the issue.
Sounds like your battery has a electrically shorted cell. When a cell is shorted out, there goes a big current from the alternator to the battery only when the engine is running. The voltage regulator inside of the alternator tries to regulate the voltage targeting the voltage around 14.4V@ambient although the battery's voltage is about 2V lower than normal and is only about 10V+some.
When a cell is shorted, voltage 14.4V is applied to the battery of 10V+some. The difference of the voltage is around 4V or so and there goes a big current like 100A or more. It is saturated by the limit of the alternator's capability and the fuse is not blown. A good battery's ESR is usually between 0.02Ω to 0.05Ω. Suppose it's 0.04Ω, there goes 133A (ie: 4V/0.04Ω≒100A). Strictly say, there is some internal impedance of the alternator but just disregard it to simplify the calculation.
I experience this type of failures time to time at local shops and dealers. Those mechanics working there are mostly not good at electric/electronics related affairs and I often am called a maestro by them. But I'm not good at mechanical affairs and they help me time to time.
I do remember v=ir from HS, but here's a question. As a general rule, does a bad battery ruin an alternator?
My uncle said no due to the voltage regulator. I thought it did. But when we think of it, typically, we know we have a bad battery because we go out one day when it's cold, and batteries are taxed, and the car cannot start. Then, we get a new battery and all is well.
A battery ruining an electrical component would be an example of a cheap part, ruining an expensive part. Just wanted to see your thoughts...
I went ahead and bought a new fusible block assembly since the alternator fuse had literally melted plastic and metal inside of the fuse holder. There may be other fuses affected by this as well. The issue I am having now is I can not find a step by step guide of removing the whole assembly, and rewiring. I bought an used assembly off ebay and it appears that the wires are cut (not a connector in place) . Are there any guides to replacing these?
Any luck i had a similar problem in my gs300 99. The 120 amp fuse would melt after a week or 2 and it turned out being frayed wires around the alternator connection
Any luck i had a similar problem in my gs300 99. The 120 amp fuse would melt after a week or 2 and it turned out being frayed wires around the alternator connection
When i change my alternator my alternator plug was burned and i pined them but 5 minutes after my car turned on i was herring music and fuse 120 blow up it could be cause the cables Pined ?
I have run into an issue with my 2003 LS that is baffling to me. I started having issues back in March with the battery and warning lights coming on while driving. I ended up having to replace the Battery, Battery fuse, Alternator fuse (replaced with a 120A instead of 140A), and electronic throttle control fuse. After all of this was done the car ran fine with no issues up until yesterday. My wife texted me on her way to work that battery light came on, as well as a few other warning lights along with a dinging sound. She works about 2 miles from home so when I got there I had her cut the car off, and back on. At this point the car would start, but no dash lights at all and could not put the car in gear. This was similar to the issue I had originally back in March with the fuses.
I had already planned at this point to look at the car on my way home to pick her up. I had her try starting the car one more time before I got there and everything seemed normal again. She got the car home, and I picked up a new alternator fuse from Lexus on my way. Well I get home and start taking the Fuse box apart to get the old fuse out and I smell a burnt plastic smell. Come to find out the Alternator fuse was not even blown, but had literally melted. I was able to get the fuse out, but looked like there was still some hardened residue left over from the fuse. I went ahead and cleaned it out the best I could using some contact cleaner, and put the new fuse in. Bolted everything back together and tried starting the car. Everything seemed normal again for a few minutes except the door ajar light was on, but no door was open from what I can see. Then all of a sudden I smell the burning electrical smell again, and smoke started coming from the fuse box. I immediately turned the car off, and disconnected the battery.
At this point I am not sure what I want to do. Most mechanical stuff I am pretty good with, but not electrical. I have checked to see if there are any loose wires anywhere near the panel, alternator, etc but I do not see anything. Anybody have any other ideas? I can get a replacement panel, but I think I saw another thread where a guy bought a new box panel, and still had the same issue of the fuses burning. Should I have the dealership diagnose the issue and see if it is something simple? I am open to all suggestions.
Four things...
First, it appears OP used an aftermarket 120 amp fuse instead of a dealer 140 amp fuse.
Second, the fuse you used is forked and has less contact surface area than OEM fuse.
Dealer purchased fuse has solid bladed contacts...
Third, perhaps you did not use screws to clamp fuse blades to bus bar?
Fourth, the OEM (dealer fuse) employs plated internals.
Above link relates to use of 140A main fuse to replace 120A main in my LS400...
I did so due to upgraded 130A alternator (LS430 engine transplant) and upgraded Alternator positive cable and negative battery cable from 6 gauge to 4 gauge.
After 20 years, replacement of all bladed fuses and fusible links can prevent overheated contacts due to contact oxidation. (=resistance)
Use Silver-plated bladed base LittelFuse from Digikey and dealer fusible links (large cube shaped fuses)
09-27-18, 05:56 AM
Alternator Fuse Melted
