# Misfire codes 16684 and 16686



## jkinsley (Feb 25, 2001)

2001 1.8T 5 speed Passat wagon with AUG engine and 115,000 miles.
I've been getting the following codes for several weeks now. These misfire codes are the only fault codes I currently get (others mentioned below have all been resolved):
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 - -
16686 - Cylinder 2 Misfire Detected
P0302 - 35-00 - -
The car has no symptoms other than the CEL coming on occasionally. When I clear the codes, they typically come back within a day or two.
I've recently done some work on the car. Things done before the misfire codes started showing up:
New Coolant Temperature Sensor (G2) to resolve code 01039 - Coolant Temperature Sensor (G2)
New MAFS to resolve code 17536 - Fuel Trim: Bank 1 (Mult): System too Lean
New timing belt, tensioner, tensioner bearing, water pump, serpentine belts (it was time)
Shortly after the timing belt replacement, the misfire codes started showing up.
Things done since the misfire codes showed up:
New coil packs (4X)
New spark plugs (4X NGK PFR6Q)
New fuel filter
New engine speed sensor (G28) to resolve code 16706 Engine Speed Sensor (G28): No Signal
I'd appreciate any ideas on what might be causing the misfire codes. Replacing the coil packs, spark plugs and fuel filter did nothing to alleviate the problem.
Thanks!
Josh


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## Golf3_R32 (Mar 10, 2005)

*Re: Misfire codes 16684 and 16686 (jkinsley)*

Maybe your timing belt is one tooth out off sync, perhaps yous hould check your valve timing.


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## dana vw tech (Sep 20, 2005)

*Re: Misfire codes 16684 and 16686 (Golf3_R32)*

It sounds like the spark area has been covered. 
I would recommend rotating the fuel injector with a different cylinder. If the misfire moves with that injector it could be the cause.
If you suspect a internal mechanical problem (worn components, excessive carbon, etc) a cranking and running compression test may reveal the problem.
I know first hand if one of those is currently out a tooth on the timing it will set a camshaft allocation fault.


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## jkinsley (Feb 25, 2001)

*Re: Misfire codes 16684 and 16686 (dana vw tech)*

Thanks for the help!
Can you tell me how the computer detects a misfire like this? I haven't felt or heard any misfire myself, so I'm wondering if it's a bad sensor. What set of sensor inputs to the computer results in a 16684 / 16686 misfire code?


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## bearthebruce (Dec 23, 2005)

*Re: Misfire codes 16684 and 16686 (jkinsley)*

I believe - although I am not certain - that the ecu looks at the crank sensor to see the speed profile between firing cylinders. When the profile does not match the prescribed profile, a misfire is declared. 
It is also possible that the ecu would use other techniques that are far more crazy - like sensing the resistance of the spark gap. On some engines, that are now cylinder pressure sensors that are used to detect the misfire.
I don't think you have a bad sensor - usually you need to look at the fuel trims and so on to determine what is happening in the engine.


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