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P1173 is an Oxygen sensor code for bank #2, indicating that the signal is incorrect. This if often times stored with a P1170 (bank #1) as well.
If this code is stored by itself, it may indicate a faulty Oxygen sensor, or a wiring issue. These codes also can indicate vacuum leaks, which are common for this engine, as well as a faulty Mass Air Flow (MAF) sensor. You would need a scantool to look at the Adaptations to know if it was a lean condition or not.
You will also want to inspect the exhaust system itself very carefully. Sometimes the catalytic converters get tiny cracks in them, where the pipe meets up with it and can cause these codes. Visible cracks or signs of black sooty residue is an indication of a crack.