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Discussion Starter · #1 · (Edited)
I just read this on a site and I was curious if anyone else has read it . What do you think?

The PCM in the vehicle calculates transmission shift points based on several sensor inputs, including MAP, Throttle position, temperature, and Mass airflow signal.
A very common cause of shift related concerns such as you describe is from using aftermarket oil impregnated air filters, such as K&N. GM has released a service bulletin (#04-07-30-013A) describing erratic transmission shifting, possibly leading to internal clutch and band damage from use of K&N air filters.
What happens is this:
The mass airflow sensor that measures the air entering the engine has a thin platinum wire placed through the path of the incoming air (if you look directly into the sensor throat, you will see this wire). The air flowing past the wire cools it, thereby changing it's resistance; the internal circuitry in the MAF sensor uses this change in resistance to change the frequency of the MAF signal. Upon engine shutdown, the PCM sends direct battery current through the MAF sensor wire to momentarily heat it up to a very high temperature to burn off any dust or small amounts of contamination that may have come in contact with it during operation.
When an oil type air filter is installed, the filter releases small amounts of oil mist into the airstream entering the engine. This oil mist coats the MAF sensor wire, contaminating it and results in it misreading the airflow rate. When the burn-off sequence occurs, any minute amount of oil tends to turn into coke-like deposits that further insulate the MAF wire, making the problem get gradually worse over time. Once this happens, the MAF sensor is destroyed; it cannot be cleaned or repaired.
The change in MAF signal that results from the contamination causes the PCM to calculate the transmission shift points incorrectly because it thinks the engine load is different than it actually is. Repeatedly applying internal friction components at the wrong time and at the wrong rate can result in premature wear and internal transmission damage. GM first came out with this service bulletin because they became aware of customers with K&N filters experiencing a higher than normal rate oftransmission failures while still under new car warranty.
I would suggest getting rid of the K&N filter and switching back to a good quality paper type filter, and installing a new mass airflow sensor. This will restore proper transmission operation unless internal damage has occurred by this point.
 

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I don't buy into this, unless someone really over-oiled their filter. Also, it is a good idea to clean the MAF sensor with alcohol every so often anyhow. Even with a paper filter, they get covered in a thin layer of dirt that, I think, would do the same thing.

FWIW, I have had a K&N filter installed on my car for 50k miles, and have 148,000+ on the odometer. Never noticed any problems, knock on wood.

Maybe on a car where the MAF was placed very close to the filter this would be a bigger issue?
 
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