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Discussion Starter #1 (Edited)
Happy Thursday Passast World!

My wonderful Passat V6 (mileage 262K) is running beautifully, been doing all the required services and necessary repairs diligently, but my engine light came on yesterday (no flashing light, the light came on and stayed). A week before that it came on too, but it went off on its own within a a day or two).

My trusted VW mechanic ran a scan and the following codes came up:

16805 – Warm up Catalyst, Bank 1
P0421 - 35-10 – efficiency below threshold – intermittent

16684 - Random/multiple cylinder misfires detected
P0300 – 35-10 –intermittent

16688 – Cylinder 4
P0304 – 35-10 – misfires detected – intermittent

16815 – Warm up Catalyst, Bank 2
P0431 - 35-10 – efficiency below threshold – intermittent

16690 – Cylinder 6
P0306 – 35-10 – misfires detected – intermittent

He cleared the engine light and said, since my car is running just fine, not to worry about it, but I want to make sure these codes/issues do not lead into something major with a huge repairs cost.

Greatly appreciate your insights and recommendations.

Thank you so much,
Ellie
 

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The misfires could be from failing coil packs. I suggest you let them be checked and replaced if needed.
 

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The misfires could be from failing coil packs. I suggest you let them be checked and replaced if needed.
It's a V6 and I believe they were replaced before IIRC. There is a TSB for this. It's possible that the ECU is too picky and needs a firmware update.


For the misfires, throw some techron fuel injector cleaner in at a double dose and run through a tank. That has helped clear up seemingly random misfires on the V6.
 
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I think the TSB was for the 00-01 models as mine fell under it. My son's 00 had been updated under warranty. I added an O2 spacer as I was above the mileage limit. The misfires will also cause the cat code. When I bought the last 2 V6 cars for our kids, I ran 2 bottles of Techron in 1/2 tank or less to do a better cleaning.
 
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Discussion Starter #5
Thank you all. I'll have coil pack checked out and also, will add Techron when tank 1/2 full.
 

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I think the TSB was for the 00-01 models as mine fell under it. My son's 00 had been updated under warranty. I added an O2 spacer as I was above the mileage limit. The misfires will also cause the cat code. When I bought the last 2 V6 cars for our kids, I ran 2 bottles of Techron in 1/2 tank or less to do a better cleaning.

The misfires could be from failing coil packs. I suggest you let them be checked and replaced if needed.
Thank you all. I'll have coil pack checked out and also, will add Techron when tank 1/2 full.
All - What's the cost looks like if I have to replace the coil pack?
 

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If the coil is bad, it's about $90 for a good Bremi replacement and about $40 for the generic brands on Ebay/Amazon.
FPC and AutoHausAZ has Bremi:
 
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If the coil is bad, it's about $90 for a good Bremi replacement and about $40 for the generic brands on Ebay/Amazon.
FPC and AutoHausAZ has Bremi:
Thank you so much PZ. Is labor more than an hour? My mechanic hourly rate is $130.00 and I'm just trying to get an idea of the total cost. Also, he generally gets good parts (not the genuine ones) from his own vendors and prices are pretty reasonable.
 

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replacing the coil pack on the v6 should take no more than 15 minutes and that includes writing the bill, washing his hands, and running your card.

All those misfires could also be failing VCGs....clogged PCV system

It is directly under the VW symbol:
98775

Remove decorative cover



(the coil pack is the first thing you see, right in front of you, on top of everything, with the six wires running out of it)
Unplug harness
Unplug 6 wires to plugs (being careful to not break that little lock thing inside them)
remove 3 10 mm bolts, one 10 mm nut, remove the little thing held on by nut, remove 10mm stud.
remove coil pack.
place a new coil pack in, go in reverse of the above.


It might be the easiest thing to change on this car.
 

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Discussion Starter #11
replacing the coil pack on the v6 should take no more than 15 minutes and that includes writing the bill, washing his hands, and running your card.

All those misfires could also be failing VCGs....clogged PCV system

It is directly under the VW symbol:
View attachment 98775
Remove decorative cover



(the coil pack is the first thing you see, right in front of you, on top of everything, with the six wires running out of it)
Unplug harness
Unplug 6 wires to plugs (being careful to not break that little lock thing inside them)
remove 3 10 mm bolts, one 10 mm nut, remove the little thing held on by nut, remove 10mm stud.
remove coil pack.
place a new coil pack in, go in reverse of the above.


It might be the easiest thing to change on this car.
Thank you so much, This is very helpful.
 

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Thank you so much, This is very helpful.
You should probably just order the coil from FCPEuro....Given the knock out video below.

This video is less than 4 minutes long. if you add the time that he explains what is going on and compare it to the amount of time he fast forwards the job in the video...you will see that if anyone has done this once...it doesn't take long.


This stupid little 10 dollar tool has saved me so much time and effort in pulling things off and not breaking it, I am pissed I didn't know it existed earlier in my life. Also works really nice for popping the wires off the coil.

98777
 

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Discussion Starter #13
You should probably just order the coil from FCPEuro....Given the knock out video below.

This video is less than 4 minutes long. if you add the time that he explains what is going on and compare it to the amount of time he fast forwards the job in the video...you will see that if anyone has done this once...it doesn't take long.


This stupid little 10 dollar tool has saved me so much time and effort in pulling things off and not breaking it, I am pissed I didn't know it existed earlier in my life. Also works really nice for popping the wires off the coil.

View attachment 98777
Thank you so much, My VW mechanic is very good and I'm sure he can handle this.
 

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Your getting misfires on #4 and #6. Generally speaking, if misfires occur on the V6 and they are not common to a coils shared cylinder, the coil pack is usually ok.
Passengers side coil is cylinder #6 and #3.
Center coil is cylinder #4 and #2.
Drivers side coil is cylinder #5 and #1.

For example, if a coil pack is at fault it would throw a code on say cylinders #4 and #2.
Not saying it can't happen but it's rare.

I think running a double dose of Techron Fuel Cleaner or Sea-Foam through the fuel system would be a good first step as mentioned already.
I would also have your mechanic check the #4 and #6 spark plug wells for oil. It could be that the valve cover is leaking and oil is seeping into the plug wells, shorting out the ignition wire thus causing a misfire. Checking the plug wells takes a few minutes of time at most.
I would say clear the codes, run for a few days with the cleaning agent and see what happens.
 

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Note that the plug wires tend to fail by your car’s age. I would replace them with some good NGK’s before the coil, which is very reliable.
 

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Discussion Starter #16
Your getting misfires on #4 and #6. Generally speaking, if misfires occur on the V6 and they are not common to a coils shared cylinder, the coil pack is usually ok.
Passengers side coil is cylinder #6 and #3.
Center coil is cylinder #4 and #2.
Drivers side coil is cylinder #5 and #1.

For example, if a coil pack is at fault it would throw a code on say cylinders #4 and #2.
Not saying it can't happen but it's rare.

I think running a double dose of Techron Fuel Cleaner or Sea-Foam through the fuel system would be a good first step as mentioned already.
I would also have your mechanic check the #4 and #6 spark plug wells for oil. It could be that the valve cover is leaking and oil is seeping into the plug wells, shorting out the ignition wire thus causing a misfire. Checking the plug wells takes a few minutes of time at most.
I would say clear the codes, run for a few days with the cleaning agent and see what happens.
Your getting misfires on #4 and #6. Generally speaking, if misfires occur on the V6 and they are not common to a coils shared cylinder, the coil pack is usually ok.
Passengers side coil is cylinder #6 and #3.
Center coil is cylinder #4 and #2.
Drivers side coil is cylinder #5 and #1.

For example, if a coil pack is at fault it would throw a code on say cylinders #4 and #2.
Not saying it can't happen but it's rare.

I think running a double dose of Techron Fuel Cleaner or Sea-Foam through the fuel system would be a good first step as mentioned already.
I would also have your mechanic check the #4 and #6 spark plug wells for oil. It could be that the valve cover is leaking and oil is seeping into the plug wells, shorting out the ignition wire thus causing a misfire. Checking the plug wells takes a few minutes of time at most.
I would say clear the codes, run for a few days with the cleaning agent and see what happens.
Thank you so much AndreasPassat. This is very helpful and will share it with my mechanic.
 

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Discussion Starter #17
Note that the plug wires tend to fail by your car’s age. I would replace them with some good NGK’s before the coil, which is very reliable.
Thank you Hirnbeiss. Changed all the spark plugs (if that's what you are referring to) with NGK a few months ago, but will ask my mechanic to check them out.
 

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And don't forget the mice chewing the wires again. Should be easy enough to notice, you only have to remove the engine covers.
 
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And don't forget the mice chewing the wires again. Should be easy enough to notice, you only have to remove the engine covers.
Yes! Thank you for the reminder PZ!

Those damn little mice, detest them with passion! It is my daily-morning routine to check my car to make sure they are not making nests there. In addition, to every evening when I get home after work to open the hood and leave it open until mid-night to let the engine to cool off, so that they don't get into my car. Despite these measures, on and off they get into my car and try to make nest under the black plastic area where the air filter and brake reservoir are, which I immediately vacuum.

However, this morning when I opened the engine cover to check out the condition of the coil pack and the sparks plugs, I noticed some stuff in the cavity under the coil pack area (see pics attached), so, I vacuumed it.

Also, attaching some pics of the coil pack and sparks plugs. And texted all the great info., you all provided to my mechanic for his review before setting up an appointment.

Thank you again PZ and everyone. Very grateful to all of you for always helping me out with your knowledge and expertise, the best Passat Forum and only one I'm a proud member of.

Wishing all of you a great weekend.



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Your two misfire codes are on the driver’s side bank. If you remove that side plastic cover you can at least confirm that there’s nothing visibly wrong with the plug wires running to those cylinders. That could be a good hiding place for mice, and it stays warm the longest.
 
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