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Engine Codes P0300, P0303, P0304


Kauz
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Hi Everyone,

I need your thoughts and experties on a problem with our RX300. Here is what I know:

-. 2000 RX300, 108K miles

-. A few days ago the check engine light came on and started blinking.

-. The engine lobes and it's seems quite likely that one or more cylinders are misfiring.

-. I got the codes and they are P0300, P0303, and P0304.

I did some search on the forum and it seems that most of the time the culprit is the ignition coil. Unfortunately the misfiring cylinders are 3 and 4 and cylinder 3 is a pain to get to. So here are my questions:

Q1. Is it possible that only one coil is bad and caused the code on the other? It seems unlikely that both coils went out at the same time.

Q2. After driving the car around the block, I parked it in the garage and looked under the hood. In the dark, I noticed that the catalytic converter was glowing red under the heat shield that covers it. I know the cat gets very hot under normal conditions, but does it actually glow? Is this caused by the unburned fuel in the cat? I had to drive the car home with this condition for about 40 miles. Could the excessive heat have damaged the cat?

Any thoughts would be greatly appreciated.

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Hi Everyone,

I need your thoughts and experties on a problem with our RX300. Here is what I know:

-. 2000 RX300, 108K miles

-. A few days ago the check engine light came on and started blinking.

-. The engine lobes and it's seems quite likely that one or more cylinders are misfiring.

-. I got the codes and they are P0300, P0303, and P0304.

I did some search on the forum and it seems that most of the time the culprit is the ignition coil. Unfortunately the misfiring cylinders are 3 and 4 and cylinder 3 is a pain to get to. So here are my questions:

Q1. Is it possible that only one coil is bad and caused the code on the other? It seems unlikely that both coils went out at the same time.

Q2. After driving the car around the block, I parked it in the garage and looked under the hood. In the dark, I noticed that the catalytic converter was glowing red under the heat shield that covers it. I know the cat gets very hot under normal conditions, but does it actually glow? Is this caused by the unburned fuel in the cat? I had to drive the car home with this condition for about 40 miles. Could the excessive heat have damaged the cat?

Any thoughts would be greatly appreciated.

The only time I have encountered a red glowing cat was becuase the honeycomb structure inside the cat had broken up and parts were blocking the exhaust flow.

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Hi Everyone,

I need your thoughts and experties on a problem with our RX300. Here is what I know:

-. 2000 RX300, 108K miles

-. A few days ago the check engine light came on and started blinking.

-. The engine lobes and it's seems quite likely that one or more cylinders are misfiring.

-. I got the codes and they are P0300, P0303, and P0304.

I did some search on the forum and it seems that most of the time the culprit is the ignition coil. Unfortunately the misfiring cylinders are 3 and 4 and cylinder 3 is a pain to get to. So here are my questions:

Q1. Is it possible that only one coil is bad and caused the code on the other? It seems unlikely that both coils went out at the same time.

Q2. After driving the car around the block, I parked it in the garage and looked under the hood. In the dark, I noticed that the catalytic converter was glowing red under the heat shield that covers it. I know the cat gets very hot under normal conditions, but does it actually glow? Is this caused by the unburned fuel in the cat? I had to drive the car home with this condition for about 40 miles. Could the excessive heat have damaged the cat?

Any thoughts would be greatly appreciated.

The only time I have encountered a red glowing cat was becuase the honeycomb structure inside the cat had broken up and parts were blocking the exhaust flow.

I agree with the above post. I would also explore if your timing is out of sync b/c of the problematic coils which would cause the glowing. The other thing that might cause a cat to glow would be a lean fuel mixture.

The fact thatthe computer is telling you about misfires would lead me towards one of the coils being bad or a bad spark plug.

Hope this helps

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Thank you all for the replies. Here is an update for those who might run into a similar situation.

The engine codes had indicated that cylinders 3 and 4 were misfiring. Since the spark plugs looked good, I figured it had to be the ignition coils. So I bought 3 new coils and put them on cylinders 1, 3, and 5 in the back. I then moved one of the good old ones from the back to cylinder 4 in front. So I'm still left with one good old coil that I will keep in the car. I figured that if another one of the old ones goes bad in the front I can easily replace it wherever I am. I also replaced all spark plugs while I was at it. After 108K miles they were overdue anyway.

So the problem is fixed and the car is running smooth again. My only concern is that I might have damaged the catlytic converter by driving the car with the condition that it was in (catalytic glowing orange red). I wish I had had it towed to my house instead of driving it 40 miles to my house. But, since I replaced the coils, the cat is not glowing anymore, which is good. Although, I still might have shortened the its life. I'll wait and see if I get any new codes. I might even get it tested if I take my car to the dealer for an alignment or something.

By the way, I read that normally any unburned fuel gets burned up inside the cat. However, the amount of unburned fuel is very small and even though the cat gets very hot it does not glow red. But, when one or more cylinders do not fire, then you have a whole bunch of unburned fuel combusting inside the cat and overheating it and causing it to glow. Driving your car under this condition will eventually melt the honeycomb structure inside the cat and ruin it (cause blockage). If this happens, then even after you fix the misfire, the cat will still probably glow orange red.

Sorry for the long post, but I thought some may find this useful and learn from my experience.

Best Regards,

Kauz

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Thank you all for the replies. Here is an update for those who might run into a similar situation.

The engine codes had indicated that cylinders 3 and 4 were misfiring. Since the spark plugs looked good, I figured it had to be the ignition coils. So I bought 3 new coils and put them on cylinders 1, 3, and 5 in the back. I then moved one of the good old ones from the back to cylinder 4 in front. So I'm still left with one good old coil that I will keep in the car. I figured that if another one of the old ones goes bad in the front I can easily replace it wherever I am. I also replaced all spark plugs while I was at it. After 108K miles they were overdue anyway.

So the problem is fixed and the car is running smooth again. My only concern is that I might have damaged the catlytic converter by driving the car with the condition that it was in (catalytic glowing orange red). I wish I had had it towed to my house instead of driving it 40 miles to my house. But, since I replaced the coils, the cat is not glowing anymore, which is good. Although, I still might have shortened the its life. I'll wait and see if I get any new codes. I might even get it tested if I take my car to the dealer for an alignment or something.

By the way, I read that normally any unburned fuel gets burned up inside the cat. However, the amount of unburned fuel is very small and even though the cat gets very hot it does not glow red. But, when one or more cylinders do not fire, then you have a whole bunch of unburned fuel combusting inside the cat and overheating it and causing it to glow. Driving your car under this condition will eventually melt the honeycomb structure inside the cat and ruin it (cause blockage). If this happens, then even after you fix the misfire, the cat will still probably glow orange red.

Sorry for the long post, but I thought some may find this useful and learn from my experience.

Best Regards,

Kauz

The downstream oxygen sensor(s), downstream of the converter, will "tell" you if the catalyst becomes not functional.

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The downstream oxygen sensor(s), downstream of the converter, will "tell" you if the catalyst becomes not functional.

That's what I was hoping. I'll keep an eye on it...

Thanks,

Kauz

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I finally caught up with this post. Eerie, kind of, as I just replaced my remaining 3 coils a few weeks ago and I have an 00 with 108k on it. Sounds like you 've got the problem fixed but I'd suggest biting the bullet and replacing the last 3 as well. Sure the front ones are easy to do but the trhee that went bad on me all went at completely random times and places. Since you'll probably be hesitant to drive it on 5 cyl. now why risk it. I figured I'd rather do mine in my garage with all my tools than in some random parking lot or worse, the side of the road. Just my 2¢.

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  • 2 weeks later...

tmastres,

That's not a bad idea. I can get the parts online for about $76 a piece which is a lot less than $91 plus tax each that I had to pay at my local Toyota delaer.

Kauz

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  • 2 years later...

Shocks....Another one of the old igniters (cylinder 6) went out. Fortunately, I was able to replace it in the parking lot with the spare one that I had from the last time and didn't have to have it towed to my house. I guess I should have replaced all of them last time. Well, no harm done. I'll just replace the 3 remaining old ones with new ones this weekend for peace of mind.

-Kauz

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  • 2 weeks later...

Shocks....Another one of the old igniters (cylinder 6) went out. Fortunately, I was able to replace it in the parking lot with the spare one that I had from the last time and didn't have to have it towed to my house. I guess I should have replaced all of them last time. Well, no harm done. I'll just replace the 3 remaining old ones with new ones this weekend for peace of mind.

-Kauz

Hello,I to have the same problem ,but I was lucky to find a part store online that sold me a set of six new ign coil for $175.00 inc S/H.

I changed all the ones in front but nothing changed.

Can someone tell me how hard it is to change the ones in the rear?

If someone can give me a step by step how to get to the 1-3-and 5 I'll really appreciate.Thank You

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