It depends on which model Saturn, if it is a V6 or a 4 cylinder. However, as a general rule there is usually one before the catalytic converter and one after it for each bank of cylinders.
〉 Answered on Oct 7th, 2012 by Jo An Holt, Automotive Journalist at Holt & Associates
I spoke with CarMD's team of ASE-certified technicians. According to our data, your 2008 Saturn Astra should have two oxygen sensors. The front is located in the exhaust manifold. The rear is located in the exhaust pipe, downstream of the catalytic converter. Incidentally, "Replace Oxygen Sensor" is the no. 4 most common check engine-related repair on that vehicle, averaging about $176 in parts and labor when you have it repaired by a professional automotive technician.
〉 Answered on Oct 7th, 2012 by Kristin Brocoff, Director of Corporate Communications at CarMD.com