2001 Volkswagen Jetta ECM code P0172

P0172 Rich Mixture, Typical symptoms of an engine that is running rich (too much fuel, not enough air).

Possible causes include a bad O2 sensor, excessive fuel pressure (bad fuel pressure regulator or plugged return line), leaky fuel injectors, dirty air filter or restricted air inlet, or a defective coolant sensor that prevents the engine management system from going into closed loop mode.