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O2 and MAF sensors troubleshooting

The following are general troubleshooting guidelines, to be used if the engine operates very badly (very rich mixture, wrong RPM, etc):

1) To easily check if the MAF sensor is working, unplug it. If engine RPM and sound does not change, it is likely not working.

2) O2 sensors are primarily diagnosed by reading their voltage thru a specific scan tool (OBDII or VAG, for example). Zero reading -- sensor is not operating.

3) If the engine is disconnected from one of the sensors used to determine the fuel mixture (MAF, O2, etc), it will default to a very rich mixture, which is detectable by the smelly and poisonous exhaust.

4) O2 sensor DOES need to be periodically replaced.

5) DO NOT buy cheap aftermarket O2 sensors that you have to wire in (splice to the old connector) yourself. Do not try to save money in the wrong place.

On VAG, O2 block is block # 032.

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