99 Boxster Check engine light issue ( Not Normal)

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Originally Posted by JFP in PA

Both codes indicate that the current to the heated O2 sensors on both engine banks is not where it should be. These are typically not a sensor or relay issue, are most commonly a wiring issue; namely high resistance or an interruption of either the heater circuit or sensor wiring. Diagnostic tree in the OBD II manual is to test the sensor (always the first step), then start testing the wiring harness heading to the DME

This is why swapping parts did not fix it, there was probably nothing wrong with the original sensors. the final step in the diagnostic tree says it all, "Repair wiring harness."

+1
Sounds like a failed harness or faulty heating circuit on the new O2 sensors... it happens:

P1117 and P1121
1. Remove connector of 02 sensor 1/2 after catalytic converter.
2. Connect ohmmeter on pin side to pins 1 and 2.
Display: 1.8 - 2.5 ohms at 20°C.
3. Connect ohmmeter on pin side to pin 1 and 02 sensor housing.
Display: infinite ohms