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Discussion Starter · #1 ·
if an error was logged because of a particualr part that needed replacing.. (of which you then replaced)... do you need to clear the error before you get benefits from the new part?

in other words... e.g. if MAF fails and throws an error. Then you replace the MAF with a new one. Do you get the benefits even without reseting the error with the VAG-COM? or would it make no difference until you clear the error?

i.e. does errors logged by the car ECU/computer accually restrict the car performance on particular areas until they are properly cleared and removed??

thanks!
Abe
 

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Some do, some don't. generally it's always best to clear the error so you know if the part you replaced fixed the problem. If your MAF sends signals way off the norm, it will most likely engage your CEL and send the car into some sort of default limp mode.
So the short answer is: Clear the error.

Alex
 

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It depends... (I know - bad answer)

Some components require "adaptation". In other words, the new part has to be calibrated in-place in order to work correctly. The most notable of these is probably the Throttle Body.

However, the MAF is just a sensor - there's nothing to calibrate, because there's nothing adjustable on the MAF. Based on my experiences cleaning my MAF sensor, I believe it's just plug-and-play.

Some ECU fault codes can result in reduced performance. For example, excess boost (IIRC, over 20 psi) can result in "limp mode" until the code is cleared (and the problem fixed). Other fault codes can trigger adaptive behavior that may reduce performance. For example, failed MAF will trigger the use of O2 sensor data for regulating fuel trim - a less-optimal method.

Some fault codes are "intermittent", while others are due to a constant malfunction. If the intermittent error goes away, the fault code is deleted after a certain number of engine starts (10, i think).

In general, the Bentley manual recommends clearing fault codes after work is performed, but this is generally done to confirm the repairs actually fixed the problem.
 

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Discussion Starter · #4 ·
thanks guys..

so are you saying then that i dont really need to worry much about replacing a MAF? i.e. plug the new MAF in and then i should expect the difference without tampering with the VAG-COM stuff...

also... what do you think of this...

"I found that there wasnt much difference between no maf and the new maf except for the Engine Light being on. The difference between the bad MAF and No MAF was really great! "

any thoughts??

thanks!
Abe
 

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It really should be plug and play... if the old MAF produced a fault code, and the new one does not, the ECU should notice the difference. For peace of mind, you could reset the ECU: open the driver's door, turn the key to on w/o starting the engine or shutting door, wait 3 minutes, turn key to off & remove. This forces the ECU to start learning its fuel trims and such from the "default" settings.

1. Bad MAF = potential for really bad fuel trims.
2. No MAF = fuel trims calculated using O2 sensors.
3. New MAF = fuel trims calculated using MAF.

(1) can be really bad if the MAF is giving inaccurate, but plausible, data.
(2) is much better than (1), but may not be as good as (3), depending on driving style & conditions.
(3) the "right" way to do it.

The ECU checks the incoming sensor data to make sure it is "plausible". In other words, it expects to see a voltage drop across the MAF within a specific range. If the MAF is giving crummy data, but is remaining within the "plausible range", the ECU buys the data lock-stock-and-barrel... resulting in poor engine behavior. However, if the MAF is unplugged, the signal from the MAF is outside of the "plausible range", so the ECU gives up and looks to the O2 sensors for data. That's why (1) can be so much worse than (2).
 
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