Wednesday, May 24, 2006

Check engine light OBD2 code P0172 on 97 VW Jetta

This P0172 obd2 code is coming on intermittently but the funny thing is, the engine runs good! What cause this obd2 code? How do you check it?

When this code shows up in your obd2 scanner, it means the bank 1 fuel trim or mixture setting is rich as calculated by your engine computer. This is determined by the oxygen sensor when it cannot make the mixture to get lean. This results in the computer commanding the injectors to spray more fuel than necessary causing the rich mixture.


1.) Oil dilution especially if the oil level is high or the engine is worn causing blow by.
2.) Plugged pcv valve when restricted will cause a built up of oil vapour in the intake.
3.) Contaminated oxygen sensor probe which can supply erroneous signal to the ecm.
4.) Bad fuel regulator if the diaphragm is ruptured causing fuel dilution
5.) Bad mass sensor but check inlet screen first.

Most likely fix:

On most of these VW Jetta models, I would start with servicing the mass sensor first since the wire element of this sensor is easily contaminated. This is very common especially if the air filter is not changed regularly. After servicing the mass sensor, reset the codes before taking it for a test drive. A detailed way of servicing the mass sensor is available from ATS including the location and color of the wiring terminals.


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