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Jeremiah Mahler
Jeremiah Mahler, ASE Certified Technician
Category: VW
Satisfied Customers: 200
Experience:  ASE Master Certified with advanced L1, California Smog Tech, Volkswagen Certified
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Customer Question

CATALYTIC CONVERTER GLOWING RED ANd I already replaced the catalytic converter because according to the mechanic that was the problem. I changed also all coils due to a misfire and this took care of the problem. as soon as that was done(changing the coils) catalytic converter still glows red hot. what is it now???
Submitted: 7 years ago.
Category: VW
Expert:  Jeremiah Mahler replied 7 years ago.
Under what circumstances is the converter glowing red? If it was after after several minutes under heavy load (up a long hill) I would consider it normal.

The ECM with all of its algorithms for detecting emissions failures should turn on the check engine light for any problem that could damage the catalytic converter. In severe cases the check engine light will flash on/off. Is the check engine light on and if so what codes are stored?

Customer: replied 7 years ago.

okay, I was barely driving a car on a hill when I started noticing the car shaking and there was a triangle on the dashboard flashing and then that's when a smelled something was burning. I stopped the car not even a minute as soon as I saw this (i couldn't just stopped in the middle of the road) and it was until I stopped all of the sensors went on and I turned off thecar, I popped the hood and there catalytic converter was glowing red. I had the car towed to my mechanic, I said that is very common on these cars the catalytic converterd go bad after having a bad coil. coil number 2 was misfiring. he just happened to have a jetta 1.8T and he just changed one coil to the one I was having trouble and it worked just fine the engine but still the catalytic converter in less than a minute glowed red. I bought the catalytic converter the old catalytic converter weights just as much as the new one and it seemed fine. nothing was melted inside. I had all coils changed now that when he tried to turn on the car another coil went bad too which was coil number 4, well, now it has alls coils changed. but once again the catallytic converter is glowing red hot What do you think it is. I don't have codes it takes a couple of minutes too turn glow red hot. as it is right now check engine light is on.....

Expert:  Jeremiah Mahler replied 7 years ago.
I would not consider the catalytic converter glowing red being a definitive test of whether it is good or bad. The ECM runs several emissions tests (readiness) on the cat and they are quite reliable in determining whether it is good or bad. These tests can be initiated using a Volkswagen scan tool (or VAG-COM).

As long as the failed ignition coils were repaired promptly the catalytic converter should not be damaged. And it usually is a good idea to replace all the coils since when one goes bad the others aren't too far behind.

Since your check engine light is on the ECM has detected a problem and it could be something that would damage the cat. This needs to be diagnosed and repaired first.

A common cause of a burning smell is a torn CV boot. You can verify this by looking for grease spatter in the wheel well or under the car.

Customer: replied 7 years ago.

the battery was unplugged I guess the codes get erased right?? what do you think it might be gettting the cat converter to get this hot??? I took the car down the border and it broke down over there.. I have it in my friends house but i don't trust the mechanics down there. to tow it back to the US is gonna cost me a lot too...


What else could it be making the car fail ?? obviously if the cat is clugged it will make it glow red but if something else is trowing too much gas too right?/ or what else could it be?? i'm talking that i need the car and I don't have much money to spend too..

Expert:  Jeremiah Mahler replied 7 years ago.
If the battery is disconnected for a few hours this should be long enough to erase the memory.

Again, I am not convinced the glowing red cat is a problem.

The best way to start finding out what is wrong is to find out what codes are stored. This could be done with a basic Generic OBD scan tool.